For the record, peer-reviewed scientific studies
have shown that transgenic (GMO) Bt corn reduces
fumonisin infestat by 95 to 98%. As you can see
from the EHP article's reference list, this is
merely the latest in a number of studies finding
the link between fumonisin infestation and
neurotube damge in new borne infants. TRD
http://www.dallasnews.com/s/dws/news/healthscience/stories/DN-corntoxin_05nat.ART.State.Edition1.3e9944f.html
Rare birth defects linked to bad corn
February 7, 2006
Knight Ridder Tribune
Laura Beil, The Dallas Morning News
Study supports corn toxin as culprit in birth defects
Evidence backs theory that diet rich in tortillas caused border epidemic
01:09 PM CST on Sunday, February 5, 2006
By LAURA BEIL / The Dallas Morning News
New data provide the strongest evidence yet that
an epidemic of rare birth defects along the
Texas-Mexico border was caused by contaminated
corn. And the findings may have implications for
populations where tortillas remain a dietary staple.
<http://www.dallasnews.com/extra>DallasNews.com/extra
03/04/2001:
<http://www.dallasnews.com/s/dws/news/healthscience/stories//sharedcontent/dws/news/longterm/stories/020506dnprocorntoxin.6ec7933c.html>Corn
toxin examined in border birth defects
For more than a decade, scientists have been
unable to explain why, starting in 1990, an
alarming number of border infants were born with
neural tube defects ?serious and even fatal
abnormalities of the brain and spinal cord that
arise in the first weeks of pregnancy. In Cameron
County alone, six babies with missing or
rudimentary brains were born in six weeks. An
investigation found a high rate of neural tube
defects among almost all border counties.
By early 1992, the epidemic had subsided as
mysteriously as it appeared. Many residents
blamed polluted water or air, and even won a
sizeable legal settlement against many of the
Mexican factories that dot the border. Yet
investigators were unable to link the disease to any man-made chemical.
As other potential explanations for the outbreak
fizzled, Texas health officials began to suspect
a naturally occurring danger: fumonisin, a toxin
from mold that can appear on corn crops. Just
before the appearance of neural tube defects
along the border, agricultural experts had noted
high concentrations of fumonisin on that year's
corn harvest, and Texas horses were experiencing
an outbreak of a fatal brain disease caused by the toxin.
In the February issue of the journal
Environmental Health Perspectives , researchers
describe results of the first study to examine
the relationship between tortilla consumption,
fumonisin exposure and the risk of neural tube
defects in people. While data in laboratory
experiments have pointed to a link, researchers
up to now have lacked human studies.
The study's major finding: Women who ate 300 to
400 tortillas per month during their first
trimester had more than twice the risk of giving
birth to a baby with a neural tube defect than
women who ate less than 100 tortillas (studies
have suggested that young Mexican-American women
along the border eat an average of 110 a month).
Blood samples taken from women also indicated
that the higher the level of fumonisin, the
greater the risk of neural tube defects.
"I don't know that we can ever go back and
definitely say that it was fumonisin," said
Lucina Suarez, director of epidemiology and
disease surveillance for the Texas Department of
State Health Services. But given this and other
research, she said, "It certainly looks that way."
Dr. Suarez and her colleagues studied
Mexican-American women who gave birth from 1995
to 2000. Diets and blood samples from women who
had babies with defects were compared with women who had normal births.
The researchers found that the correlation with
tortilla consumption disappeared when women ate
more than 400 corn tortillas per month,
suggesting that above a certain level, a
fumonisin-exposed fetus might not survive.
Laboratory studies have found that fumonisin
interferes with the absorption of folic acid,
which protects against neural tube defects.
But even with the new research, experts still
cannot say with certainty that the epidemic in
South Texas was the work of fumonisin. They may
never be able to: The corn from that time is long gone.
"It absolutely is plausible," said David Miller
of Carleton University in Canada, who is one of
the world's foremost authorities on the toxin.
However, he added, "Let me tell you what we don't
have. We do not have direct human evidence." In
other words, the study can't rule out other explanations.
Nonetheless, more scientific inquiry is needed,
Dr. Miller said, because fumonisin can still
creep into the corn supply when the crops are
stressed and because many people's diets heavily
depend on tortillas. "We need to know the answer to this question," he said.
Both the World Health Organization and the U.S.
Food and Drug Administration set limits on the
amount of fumonisin allowed in corn products.
Those limits were set before much of the recent
research. Dr. Miller said he believes that, even
if fumonisin should prove to increase the risk or
birth defects, the allowable levels are still safe.
Through a spokesman, officials from the FDA said
they would not discuss the Environmental Health Perspectives report.
"There seems to be some connection between
tortilla consumption and neural tube defects,"
said Ron Riley, a fumonisin expert from the U.S.
Department of Agriculture. But he is still
waiting for further study before making up his
mind about whether the tortillas themselves were
to blame. "It's supportive, but it's not
convincing," he said. "With regard to fumonisin, the jury is out."
E-mail <mailto:lbeil@dallasnews.com>lbeil@dallasnews.com
-----------------------------------------------------------------
http://www.dallasnews.com/s/dws/news/longterm/stories/020506dnprocorntoxin.6ec7933c.html
Corn toxin examined in border birth defects
Diet may have put Hispanics at risk
05:30 PM CST on Saturday, February 4, 2006
By LAURA BEIL / The Dallas Morning News
Editor's Note: This story first appeared in The
Dallas Morning News on March 4, 2001.
The nurses at Valley Regional Medical Center in
Brownsville sensed something more than a horrible
coincidence. Two babies born the same day in
April 1991 had brains that were stunted or
missing, a rare defect that usually strikes only
three or four births in 10,000.
Stunned, nurse Connie Riezenman called the Texas
Department of Health. Before state officials
could respond hours later, doctors had delivered
a third, tragically malformed infant.
"I felt frantic," she said. "It was just too
scary." In the next six weeks, three more women
gave birth to misshapen newborns at her hospital.
State and national investigators would eventually
find that Brownsville had an astonishingly high
rate of anencephaly, as the condition is called.
From 1989 through 1991, 32 women in this town of
130,000 carried anencephalic babies. Many of the
children died within hours, and all within days, of birth.
Then, in 1992, the anencephaly rate ebbed as unexpectedly as it had risen.
Still searching for a cause, many experts keep
circling back to one of the few explanations for
an epidemic that can come and go on its own: a
natural poison that crept in and out of the food
supply. Disease investigators have focused on a
common toxin found in corn, a mainstay of a
traditional Mexican-American diet. If this toxin
is indeed responsible for the birth defects that
stalked the Lower Rio Grande Valley - and no one
has yet concluded that it is - then Texas health
officials worry about other effects in Hispanics.
In addition to birth defects, the chemical may
increase the risk for esophageal and liver cancer.
The outbreak of 1991 remains unsolved. From the
beginning, many residents suspected the
pesticides that armor nearby fields of cotton and
sorghum. Others blamed the chemicals that waft
from industries along the Rio Grande. Some
parents of affected infants even shared a $17
million settlement from more than 80 maquiladoras
- U.S. factories hugging the Mexican side of the river - in 1995.
But now, state health officials wonder whether
the culprit was not man-made, but a natural
fungus that can cling to corn. The fungus makes a
toxin , called fumonisin, unknown to science until 1988.
Texas health officials learned of it in 1992. "We
didn't even know how to spell it," said Dr. Kate
Hendricks of the state's infectious-disease
division. Since then, Dr. Hendricks and her
colleagues have found themselves becoming armchair authorities on corn mold.
Given fumonisin's potential to cause disease, a
U.N. committee will soon release its first report
recommending a daily limit on human exposure to
the toxin . Last summer, the U.S. Food and Drug
Administration announced possible guidelines for
the maximum amount of fumonisin in corn intended
for human food. The agency recommends no more
than 4 parts per million for masa and similar corn products.
But the FDA number, state officials argued in a
three-page response, may be too high for those
who depend on corn for their daily bread. "There
is clear evidence," state officials warned, "that
fumonisins are carcinogenic in some animal
species and sufficient evidence indicating that
these compounds may be able to affect the neural development of the fetus."
They urged that any decision on fumonisin levels
"take into consideration the consumption patterns
of the Texas Hispanic population," concerns that
FDA officials say they are heeding.
Tracking the poison
Fumonisin (pronounced few-MAHN-i-sin) is spit out
by the mold Fusarium as part of its chemical
defense system. For decades, farmers and ranchers
have known that animals can fall seriously ill if
they eat corn that has been coated with Fusarium,
even if the kernels later seem clean. People in
parts of the world with high Fusarium growth,
most notably the Transkei region of South Africa,
have high rates of esophageal cancer.
But it wasn't until 1988, when South African
scientists first described fumonisin, that anyone
knew exactly why the mold was dangerous.
One of the more peculiar traits of fumonisin is
its ability to cause vastly different diseases in
different animal species. Pigs that eat
fumonisin-contaminated corn can develop pulmonary
edema, a condition in which their lungs fill with
fluid. The most sensitive animals appear to be
horses, which get a crippling brain disease called leukoencephalomalacia.
In humans, hints of the esophageal and liver
cancer risks come from studies in rats, and from
parts of the world - such as the Transkei and
certain areas of China - with frequent fumonisin
contamination of corn. Health officials note that
these regions also have high rates of the same
birth defects that appeared in the Rio Grande
Valley. But this kind of research doesn't address
the possibility of a coincidence.
Possible fetal effects
Anencephaly, which befell Brownsville's babies,
is one of a cluster of abnormalities called
neural tube defects. The most common is spina
bifida. The defects occur soon after conception,
at a time when a woman wouldn't even know she is
pregnant. They happen when the cells of the
embryo that will create the central nervous
system don't wrap around themselves and form a
tube during development. Sufficient levels of
folic acid, a B vitamin, will protect against neural tube defects.
In 1997, researcher Victoria Stevens of Emory
University in Atlanta offered a possible
connection between fumonisin and folic acid. In
test-tube experiments, she found that fumonisin
interfered with a cell's ability to absorb the
vitamin. If this is true in the womb, then
fumonisin might starve a developing embryo of its protection.
"There's a biologically plausible mechanism," Dr.
Stevens said. She is quick to add, however, that
this is only a theory, and hers is only one
study. Without a lot more research, no one can
say whether what happens in a laboratory is
actually what causes neural tube defects during pregnancy.
While lacking proof that ties fumonisin to the
tragedy along the border, Texas health officials
are nonetheless impressed by the circumstantial
evidence. For one thing, if pollutants caused the
birth defects, why, then, did the outbreak
subside? Surveys found that even after folic acid
awareness campaigns, childbearing women in
Brownsville had not begun to dramatically
supplement their diets with the nutrient.
"Whatever caused that [outbreak] ... didn't stay
there forever," Dr. Hendricks said. "Man-made
chemicals would not have disappeared."
Corn connections?
Fumonisin, however, is as unpredictable as the
weather. Fusarium mold grows on corn plants under
stress from heat, insects or other causes. In
1988, a blistering drought left corn farmers with
one of their worst harvests in years. Crop
reports show that by August and September, about
half the country's cornfields were listed as
"poor" or "very poor." Conditions improved in
1989, with more than half the late-summer crops described as good or better.
Still, no one can say whether corn plants
themselves from the late 1980s were contaminated.
Agriculture officials do know that in late 1989,
corn-fed horses across the nation began dying
from leukoencephalomalacia, or ELEM.
"We began to get daily phone calls from state
labs, veterinary hospitals with what they
regarded as ELEM cases," said Frank Ross, head of
toxicology for the National Veterinary Services
Laboratory in Ames, Iowa. "We would typically
hear of a few of these a year." The outbreaks
lasted through the winter of 1990.
Recognizing the fingerprints of fumonisin, Dr.
Ross' laboratory found that toxin levels in
corn-based horse feed at the time typically
exceeded 10 parts per million. Some reached the
surprising level of 126. Also in 1989, an unusual
number of pigs began contracting pulmonary edema.
Iowa State University researchers found that
fumonisin in corn needed to rise above 50 parts
per million to give pigs the deadly lung disease.
At the same time, livestock were falling ill from
fumonisin, neural tube defect rates around
Brownsville were creeping upward, mostly driven
by rises in anencephaly. But no one would notice
this trend until the three births at Valley
Regional summoned state and federal disease investigators in 1991.
Then, in 1992, the state chemist called Texas
health officials. Did they know that a state
screening program for animal feed was finding
fumonisin levels approaching 70 parts per
million? Operators transferred the call to Dr.
Hendricks. "Fumonisin?" she asked, puzzled. She
and her colleagues began scouring for information.
"What we read made us very concerned," Dr.
Hendricks said, their thoughts lingering on the
border outbreak. If fumonisin had infiltrated the
corn supply, they reasoned, the most serious
effects would show up in the biggest corn eaters.
Canadians, who eat only about 17 grams of corn a
day on average, probably wouldn't need to worry.
But Mexican-American women along the border eat
more than five times that amount per day in tortillas alone.
By this time, the border outbreak had quieted.
Plus, no one could test corn eaten in 1989 and
1990, about the time women affected by the
outbreak would have become pregnant.
Tortilla tests
A continent away, though, researchers in South
Africa had already screened corn from the U.S.
food supply. By coincidence, they were studying
fumonisin levels in five countries. They bought
corn in various incarnations - including
tortillas - in 1990 and 1991. The researchers
found fumonisin in one-third of the U.S.
tortillas they tested. The concentrations were
less than 1 part per million; nonetheless, the
fumonisin content of most of the U.S. corn
products dwarfed amounts in the products from
other countries. The South African samples
generally had the second-highest levels.
The findings, scientists wrote in 1991 in the
Journal of Agricultural and Food Chemistry,
"clearly indicate for the first time that
consumers of corn-based commercially available
foodstuffs in the United States and South Africa
are exposed to elevated levels of the fumonisins."
The numbers might be even higher were it not for
the slow journey from corn to masa to tortilla.
Ancient methods of steeping, washing and grinding
transform corn and water into an enchilada
wrapper or crispy chip. During the half-dozen or
so stages, the kernels take a long, hot bath in
lime and shed their hulls. These steps drastically reduce fumonisin levels.
Studies led by U.S. Department of Agriculture
scientist Mary Ann Dombrink-Kurtzman in Peoria,
Ill., have found that tortilla making can slash
the level of fumonisin in raw corn by as much as
80 percent. To come up with that number, she and
Texas A&M University researcher Lloyd Rooney took
samples from laboratory-made tortillas at every point from corn through oven.
However, she notes, "this doesn't answer what
people in their homes may be doing during their processing."
Over the last three years, Dr. Dombrink-Kurtzman
has examined nearly 2,000 cornmeal samples from
the U.S. milling industry, gathered amid routine,
voluntary screening for fumonisin that started in
1998. Given the levels she has found, along with
the reductions through cooking, she has
calculated that U.S. corn tortillas these days
would contain between 0.02 and 0.2 parts per million.
"I still eat a lot of tortillas," Dr.
Dombrink-Kurtzman said. "I think the corn is
safe." However, her studies of Mexican masa and
tortillas have found much greater concentrations.
Some of those samples approached 2 parts per
million. These higher figures, she said, might be
expected from regions where drought often strains corn crops.
Hispanic health
These and other recent analyses suggest that
current fumonisin concentrations in tortillas are
low. But Texas health officials also think about
their research showing that Hispanic women along
the border eat, on average, about 110 corn tortillas a month.
Still, if corn is a staple among
Mexican-Americans across the state, why would
fumonisin's damage show up only in Cameron
County? No one can say with certainty that
Brownsville was unusual, Dr. Hendricks replies.
Before 1993, birth defects were not carefully
monitored in Texas, or in most places across the
country, she said. "You can miss an increase rather easily."
"You have to think why we got called," she added.
Had the three terrible births at Valley Regional
hospital not occurred, the outbreak might have escaped notice.
There are some signals that more anencephalic
births than usual were occurring nationwide in
1991. The available data suggest that the
national rate was about 18 per 100,000 births
that year. The number fell to 13 in 1992, where
it has more or less hovered, dropping as low as 10 in 1998.
Available records also suggest that across Texas
in 1992, Hispanic mothers continued to have
anencephaly rates more than twice those of
non-Hispanic whites and three times those of black mothers.
Texas health officials acknowledge that none of
this proves that fumonisin caused the outbreak a
decade ago. "It's a strong hypothesis," Dr. Hendricks said.
Skeptical, but ...
Some of the country's top fumonisin experts remain intrigued, but unconvinced.
"What do we know? We know there was a spike" in
fumonisin in 1989 corn, said Dr. David Miller of
Carleton University in Canada. "We know the
potential exists" for a connection to neural tube
defects, given the Emory experiments."
But he adds, "We have to be careful about associations."
The USDA's Ron Riley, who also studies fumonisin,
is skeptical about any link, largely because
animals eating the toxin don't appear to get
birth defects. "We know that pigs eat a lot of
[low-quality] corn ... but I've never seen a report of a neural tube defect."
Yet he believes the idea calls for further
scientific investigation. "I don't want there to
be a connection," Dr. Riley said. "There's a lot
to lose if we start talking about corn being bad
food. ... My gut feeling is there's no
connection, but I keep coming back to the 'what if?' "
"What if?" also nags Texas health experts. No one
doubts that fumonisin causes disease in a variety
of animals, Dr. Hendricks said. It would be
unlikely that people are somehow spared. Federal
officials, when setting the safety thresholds for
fumonisin, should think carefully about those who
depend largely on corn, she and her colleagues contend.
FDA officials say they are doing this.
"Yes, we are mindful of corn consumption by
particular population groups," said Mike Bolger,
of the agency's Center for Food Safety and
Applied Nutrition. "We had that in mind when we
came up with this level." He said any tie to
neural tube defects or cancer is, for now, little more than a theory.
"We're not saying fumonisin is a non-problem,"
Dr. Bolger said. "We're spending time, resources
and energy to figure out what's going on."
For 10 years, families along the border have also
wanted to know what's going on.
"People think it was something in the water,
something in the air," nurse Riezenman said. But
until anyone gives them an answer, they will
wonder whether an epidemic will suddenly strike their babies again.
"Like any community that's experienced something
dreadful," she said, "it's always in the back of your mind."
---------------------------------------------------------------------
http://ehp.niehs.nih.gov/members/2005/8221/8221.pdf
http://ehp.niehs.nih.gov/members/2005/8221/8221.html
<http://ehp.niehs.nih.gov/docs/2006/114-2//docs/2005/8221/abstract.html>NEURODEVELOPMENT
| Fumonisin Exposure and Neural Tube Defects
The incidence of neural tube defects (NTDs) among
women along the Texas-Mexico border doubled
during 1990-1991. The outbreak began during the
same crop year as an epizootic, which was
attributed to exposue to fumonisin, a mycotoxin
contaminate in corn. In populations consuming
large quantities of corn, humans, as well as
livestock, may be exposed to high levels of
fumonisins. Using a population-based case-control
study,
<http://ehp.niehs.nih.gov/docs/2006/114-2//docs/2005/8221/abstract.html>Missmer
et al. (p. 237) examined whether or not maternal
exposure to fumonisins increases the risk of NTDs
in offspring. Findings suggest that fumonisin
exposure increases the risk of NTD, proportionate
to dose, up to a threshold level, at which point
fetal death may be more likely to occur.
<http://ehp.niehs.nih.gov/members/2005/8221//cgi-bin/findtoc2.pl?tocinfo=Environmental
Health Perspectives@114@2@2006>Environmental
Health
Perspectives<http://ehp.niehs.nih.gov/members/2005/8221//cgi-bin/findtoc2.pl?tocinfo=Environmental
Health Perspectives@114@2@2006> Volume 114, Number 2, February 2006
[]
Research
Exposure to Fumonisins and the Occurrence of
Neural Tube Defects along the Texas-Mexico Border
Stacey A. Missmer,1,2 Lucina Suarez,3 Marilyn
Felkner,3 Elaine Wang,4 Alfred H. Merrill Jr.,4
Kenneth J. Rothman,5 and Katherine A. Hendricks6
1Department of Epidemiology, Harvard School of
Public Health, Boston, Massachusetts, USA;
2Department of Obstetrics, Gynecology, and
Reproductive Biology, Brigham and Women's
Hospital and Harvard Medical School, Boston,
Massachusetts, USA; 3Texas Department of State
Health Services, Austin, Texas, USA; 4School of
Biology, Georgia Institute of Technology,
Atlanta, Georgia, USA; 5Department of
Epidemiology, Boston University School of Public
Health, Boston, Massachusetts, USA; 6Medical Institute, Austin, Texas, USA
*
<http://ehp.niehs.nih.gov/members/2005/8221/#intro>Introduction
* <http://ehp.niehs.nih.gov/members/2005/8221/#meth>Materials
and Methods
* <http://ehp.niehs.nih.gov/members/2005/8221/#resu>Results
*
<http://ehp.niehs.nih.gov/members/2005/8221/#disc>Discussion
Abstract
Along the Texas-Mexico border, the prevalence of
neural tube defects (NTDs) among Mexican-American
women doubled during 1990-1991. The human
outbreak began during the same crop year as
epizootics attributed to exposure to fumonisin, a
mycotoxin that often contaminates corn. Because
Mexican Americans in Texas consume large
quantities of corn, primarily in the form of
tortillas, they may be exposed to high levels of
fumonisins. We examined whether or not maternal
exposure to fumonisins increases the risk of NTDs
in offspring using a population-based
case-control study. We estimated fumonisin
exposure from a postpartum
sphinganine:sphingosine (sa:so) ratio, a
biomarker for fumonisin exposure measured in
maternal serum, and from maternal recall of
periconceptional corn tortilla intake. After
adjusting for confounders, moderate (301-400)
compared with low ( 100) consumption of tortillas
during the first trimester was associated with
increased odds ratios (ORs) of having an
NTD-affected pregnancy (OR = 2.4; 95% confidence
interval, 1.1-5.3). No increased risks were
observed at intakes higher than 400 tortillas (OR
= 0.8 for 401-800, OR = 1.0 for > 800). Based on
the postpartum sa:so ratio, increasing levels of
fumonisin exposure were associated with
increasing ORs for NTD occurrences, except for
the highest exposure category (sa:so > 0.35). Our
findings suggest that fumonisin exposure
increases the risk of NTD, proportionate to dose,
up to a threshold level, at which point fetal
death may be more likely to occur. These results
also call for population studies that can more
directly measure individual fumonisin intakes and
assess effects on the developing embryo. Key
words: case-control study, corn, fumonisins,
Mexican Americans, mycotoxins, neural tube
defects. Environ Health Perspect 114:237-241
(2006). doi:10.1289/ehp.8221 available via
<http://dx.doi.org/>http://dx.doi.org/ [Online 29 September 2005]
Address correspondence to L. Suarez, Texas
Department of State Health Services, Epidemiology
Research Services Branch G-401, 1100 West 49th
St., Austin, TX 78756-3199 USA. Telephone: (512)
458-7729; Fax: (512) 458-7229. E-mail
<mailto:lucina.suarez@dshs.state.tx.us>lucina.suarez@dshs.state.tx.us
We thank L. Marks for assistance on the seasonal
fumonisin data; M. Trucksess, U.S. Food and Drug
Administration, for the tortilla analyses; and D.
Miller and J. Villanacci for their helpful insight.
Funding was provided by Centers for Disease
Control and Prevention (CDC) Birth Defects Branch
cooperative agreement U85/CCU608761-05 and Texas
Birth Defects Research Center/CDC cooperative
agreement U50/CCU613232. P. Blackshear (National
Institute of Environmental Health Sciences)
provided funding for laboratory services so that
the second batch of serum could be tested.
The authors declare they have no competing financial interests.
Received 18 April 2005; accepted 29 September 2005.
[]
Introduction
In 1990-1991, an outbreak of neural tube defects
(NTDs) occurred in Cameron County, Texas (USA), a
south Texas county bordering Mexico wherein six
anencephalic births occurred in 6 weeks at one
hospital. NTDs are embryonic defects of the brain
and spinal cord resulting from failure of the
neural tube to close. Spina bifida and
anencephaly (failure of anterior tube closure)
are the most common forms of NTD. Investigation
of the cluster revealed a high prevalence of NTDs
in this region (27 per 10,000 live births) (Texas
Department of Health, unpublished report) that
proved endemic to the entire Texas-Mexico border
region. Just before the NTD outbreak, in the fall
of 1989, an outbreak of equine
leukoencephalomalacia (ELEM)--liquefaction of the
white matter of the brain in horses--occurred
nationwide. It was particularly severe in Texas,
where, in contrast to the usual one to five ELEM
clusters reported, > 40 clusters were reported in
< 2 months (Reagor J, personal communication). As
an empiric preventive measure, livestock were
taken off feed containing corn, because the corn
harvest that year was thought to be contaminated
with mold (Ross et al. 1992). Humans continued to
eat corn from this harvest. The corn contaminant
that led to the ELEM epizootic was a class of
mycotoxins called fumonisins, produced by the
molds Fusarium verticillioides (sometimes and
formerly referred to as Fusarium moniliforme) (Seifert et al. 2003).
Multiple observations suggested that the NTD
outbreak and the epizootics shared a common
etiology. Cornmeal samples collected in the
United States during the NTD outbreak had
relatively high average fumonisin levels
(Hendricks 1999). Other regions with high
corn-based food consumption and documented
fumonisin contamination (Dombrink-Kurtzman and
Dvorak 1999; Yoshizawa et al. 1994) also have
high prevalences of NTDs (Moore et al. 1997;
Mutchinick et al. 1999). Recent in vitro and
animal studies provide further support for the
hypothesis that NTDs occur with exposure to
fumonisins (Flynn et al. 1997; Gelineau-van Waes
et al. 2005; Sadler et al. 2002; Stevens and Tang 1997; Wang et al. 1991).
In this study, we examined whether or not
maternal exposure to fumonisins increases the
risk of NTDs in offspring. This examination,
using a population-based case-control study,
represents the first epidemiologic assessment of
the association of NTD occurrence and fumonisin
exposure. We estimated fumonisin exposure from
postpartum sphinganine:sphingosine (sa:so) ratio,
a biomarker for fumonisin exposure measured in
maternal serum, and from maternal recall of
periconceptional corn tortilla intake.
Materials and Methods
Study population. We identified study
participants through the Texas Department of
Health's Neural Tube Defect Project. Participant
identification and data collection methods have
been described previously in detail (Hendricks et
al. 1999; Suarez et al 2000). In brief, the
project included multisource active surveillance,
a case-control study to identify risk factors for
NTD occurrence, and a follow-up folic acid
intervention program to reduce NTD recurrence.
Cases (infants or fetuses) had a diagnosis of
anencephalus [International Classification of
Diseases, 9th RevisionClinical Modification
(ICD-9-CM) (Medicode, Inc. 1993)] code 740, spina
bifida (741), or encephalocele (742.0) and
included live births, stillborns, and prenatally
diagnosed fetuses at all gestational ages. For
this study, we defined case women as
Mexican-American women with NTD-affected
pregnancies who resided and delivered in one of
the 14 Texas-Mexico border counties from March
1995 through May 2000. We identified control
women from Mexican-American residents of the same
study area who delivered normal live births
during the same period. Control women were
randomly selected annually, frequency matched to
case women by facility and year. Facilities
included hospitals and midwife-attended birthing centers.
Data collection. The Texas Department of Health
Institutional Review Board approved the study
design, English-Spanish consent forms,
English-Spanish interview instruments, specimen
collection, and study procedures. In cooperation
with hospital staff, field teams contacted women
at the time of delivery or termination of
pregnancy to inform them of the study and obtain
consent. All women in the study gave written
informed consent, in their preferred language
(English or Spanish), before participation in the study.
Women were interviewed in person about 5-6 weeks
postpartum with an interview instrument modeled
after the 1993 Centers for Disease Control and
Prevention (CDC) mother questionnaire for birth
defects risk factor surveillance. The
questionnaire assessed maternal health history,
demographics, use of medications and nutritional
supplements, and environmental and occupational
exposures during the periconceptional period--the
3 months before conception and the 3 months after
conception (first trimester of pregnancy). Before
each interview, the staff
obstetrician/gynecologist and interviewer
estimated the date of conception for the index
pregnancy using all gestational age estimates
from the medical records. Women were specifically
asked about corn tortilla consumption during
periconception, including the type (brand name,
homemade), the month consumed, the frequency
(number of days per month), and quantity (number
of tortillas per day). We calculated body mass
index (BMI; kilograms ?meter2) from
self-reported prepregnancy height and weight.
Women were paid $20 for the 2-hr interview. Blood
and urine samples were also collected, for which
women were paid an additional $20.
Laboratory procedures. Maternal blood specimens
were collected in 13 mL tubes without
anticoagulant. After coagulation and
centrifugation, 3 mL aliquots of serum were
apportioned into cryovials. These aliquots were
frozen at 20蚓 and shipped overnight on dry ice
to Emory University Laboratory (Atlanta, GA).
Analysis of the sa:so ratio in serum was
conducted by high-performance liquid
chromatography with fluorescent detection of
these compounds as the ortho-phthalaldehyde
derivatives (Riley et al. 1994). Fumonisins
inhibit ceramide synthase, which results in an
elevation of sphinganine, a potentially toxic
intermediate of de novo sphingolipid biosynthesis
(Merrill et al. 2001; Riley et al. 2001; Wang et
al. 1991). Because sphingosine is formed during
turnover of complex sphingolipids, its amount is
affected less by fumonisins; hence, the sa:so
ratio is a surrogate measure of fumonisin
exposure. Owing to funding restrictions, the
laboratory conducted the sphinganine and
sphingosine analyses in two separate batches,
each containing case and control samples. The
Division of Laboratory Sciences of the CDC
performed serum folate and B12 analyses using the
same procedure as that used for the Third
National Health and Nutrition Examination Survey
(Gunter et al. 1996). The long-term total
analytical coefficient of variation for these
assays over 6 years was approximately 5%.
To estimate fumonisin levels in tortillas, we
collected samples of tortillas from participant
homes and local grocery stores throughout the
study period. A total of 146 households
contributed tortilla samples, and another 114
samples were obtained from grocery stores.
Tortillas were placed in plastic reclosable
sandwich bags and labeled with the date of
collection, brand of tortilla, and place of
tortilla purchase. The samples were frozen at 0蚓
until shipped, and then shipped in cold packs
overnight to the Division of Natural Products
laboratory at the U.S. Food and Drug
Administration (FDA). Of the multiple structural
isoforms of fumonisin B1 (FB1), fumonisin B2
(FB2), fumonisin B3 (FB3), we report only FB1
levels; FB2 and FB3 levels were essentially
nondetectable. FB1 levels were determined using
high-pressure liquid chromatography (Stack 1998).
Statistical analysis. Of the 225 Mexican-American
women with NTD-affected pregnancies and 378
Mexican-American women with healthy live births
identified for study, 184 case women and 225
control women participated in the interview.
Twenty-six case women (12%) and 101 control women
(27%) refused to be interviewed, and 15 case
women (7%) and 52 control women (14%) had moved
out of the study area without being interviewed.
Of those interviewed, 163 case women (89%) and
189 control women (84%) provided blood specimens for the sa:so assay.
We evaluated two direct exposure metrics:
fumonisin exposure as measured by the sa:so ratio
assayed from the maternal blood sample, and total
number of corn tortillas eaten during the first
trimester of pregnancy as reported on the
mothers' questionnaires. We chose categorical
cut-points for presentation of the fumonisins and
continuous corn exposure variables by calculating
the effect of finely categorized variables and
then coalescing adjacent categories based on the
observed effect estimates (Greenland and Rothman 1998).
In addition, we calculated a third metric based
partially on ecologic data: nanograms of
fumonisins ingested per day during the
periconceptional period as estimated from grouped
6-month averages for the tortilla samples. To
control for possible seasonal variability, we
categorized dates of conception into 6-month
blocks, beginning with February-July 1994 and
ending with August 1999-January 2000. We chose
these categories based upon the timing of the
entry of new corn crops into the U.S. market for
human purchase and consumption (Miller D,
personal communication). We linked each woman's
date of conception to the average fumonisin
levels found in tortillas collected during that
6-month block. Daily dose of fumonisin exposure
was calculated by multiplying the average
fumonisin level (nanograms per gram) by 24 g per
tortilla (the average weight of collected
samples) and then by the number of tortillas the
woman reported eating per day during the first
trimester of pregnancy. That number was then
divided by the woman's weight in kilograms.
Using the SAS statistical software package
(Version 8, SAS Institute 1991), we fit a
logistic regression to calculate deconfounded
odds ratios (ORs) and 95% confidence intervals
(CIs) to estimate prevalence ratios of NTDs. We
considered other possible risk factors for NTDs
as potential confounders if addition of that
variable to the model changed the OR by 10% or
greater. Confounding checks were performed in
both univariate and final multivariate models. If
a factor was identified as a confounder of any
estimated main effect, it was kept in all models.
Based on these criteria, we controlled for BMI
(kilograms per square meter, continuous), serum
B12 (picograms per milliliter, continuous), and
dates of conception (6-month blocks). In
addition, the sa:so values were found to differ
systematically by batch (batch 1: n = 172, ratio
median = 0.19, 5th percentile = 0.08, 95th
percentile = 0.36; batch 2: n = 180, ratio median
= 0.13, 5th percentile = 0.08, 95th percentile =
0.24), and therefore we adjusted for batch in all
sa:so analyses. Known NTD risk factors that were
not confounders within this population included
maternal age, maternal birthplace, annual
household income, folate intake (dietary plus
multivitamin), and prior pregnancy loss. Finally,
because it is unclear whether serum folate levels
are a measure of an intermediate variable between
the main corn/fumonisin effects and NTDs or
whether serum folate is a potential confounder,
we fit models with and without adjustment for serum folate.
Results
Table 1.
<http://ehp.niehs.nih.gov/members/2005/8221/tab1.jpg>
Table 1
Table 2.
<http://ehp.niehs.nih.gov/members/2005/8221/tab2.jpg>
Table 2
Table 3.
<http://ehp.niehs.nih.gov/members/2005/8221/tab3.jpg>
Table 3
Table 4.
<http://ehp.niehs.nih.gov/members/2005/8221/tab4.jpg>
Table 4
The demographic profile of control women
illustrates the low socioeconomic conditions
prevalent on the border. More than a third
reported a household income of < $10,000 per
year, and only about half had completed high
school (Table 1). Control women were leaner and
more educated than were case women but comparable
in age. Few women reported ever taking preconceptional folic acid supplements.
Nearly all women consumed corn tortillas (96% of
case women and 93% of controls). As seen in Table
2, control women reported an average consumption
of two tortillas per day during their first
trimester of pregnancy (180 total during this
3-month period). That number was nearly identical
to the intake reported during the 3 months before
conception. Most women purchased rather than made corn tortillas.
After adjustment for BMI, serum B12, and date of
conception, moderate (301-400) compared with low
( 100) consumption of tortillas during the first
trimester was associated with an increased OR of
having an NTD-affected pregnancy (OR = 2.4, 95%
CI, 1.1-5.3) (Table 3). Higher intakes (401-800
and > 800) were associated with either a slight
decrease in occurrence (OR = 0.8 for 401-800) or
no effect (OR = 1.0 for > 800). The type of
tortilla usually consumed appeared to affect
risk. NTD risk increased with exposure to
homemade tortillas (OR = 2.9; 95% CI, 1.4-5.9)
(Table 3). Among those who purchased tortillas,
the effect estimates differed slightly by brand,
but the CIs for individual brands were wide (data
not shown). As shown in Table 3, increased
exposure to fumonisins, based on postpartum sa:so
ratio, was associated with an increased NTD
occurrence except for the highest exposure
category. The highest exposure category (sa:so >
0.35) was related to less frequent occurrence (OR
= 0.7, 95% CI, 0.2-2.9) but was based on the
fewest number of subjects and therefore had a
wide CI. Results differed negligibly when serum folate was added to the model.
The mean fumonisin level measured in the 240
tortilla samples was 234 ng/g (range = 0-1,690
ng/g; SD = 256). When fumonisin levels by season
were linked to dates of conception, the median
daily fumonisin exposure (nanograms per day per
kilogram of weight) was 172.6 for case women and
156.1 for control women. Using the imputed
exposure levels for individual women, we also
observed an inverted U-shape relation to risk,
reflecting the tortilla consumption pattern (Table 4).
Discussion
Our findings from the postpartum serum sa: so
measure suggest that fumonisin exposure increases
the risk of NTD, proportionate to dose, up to a
threshold level. Data on the corn tortilla
consumption and fumonisin ingestion appear to
support an inverted U-shaped pattern of
occurrence. This pattern may reflect the
formation of NTDs up to a threshold of damage, at
which point fetal death is more likely to occur.
Because true biologic incidence is impossible to
determine, the prevalence of birth defects is a
function of embryologic incidence as well as
intrauterine survival (Weinberg and Wilcox 1998).
Additionally, experiments demonstrate that fetal
resorption can occur in folate-deficient pregnant
mice (Burgoon et al. 2002) as well as in hamsters
and mice exposed to high doses of FB1 (Floss et
al. 1994; Gelineau-van Waes et al. 2005; Reddy et al. 1996).
We also observed a difference in risk effect
between manufactured tortillas and homemade
tortillas. The variations in small-scale tortilla
preparation, especially the corn-to-lime ratio,
results in wide variations in residual fumonisins
(De La Campa et al. 2004). If tortillas made at
home have a consistently lower concentration of
lime or poorer quality corn is used, this could
potentially explain some of the increased effect
seen in homemade tortillas (De La Campa et al. 2004).
Alternative explanations for the effects that we
observed include concern about the potential for
recall bias in the estimate of tortillas consumed
and lack of a true biomarker of fumonisins at the
time of neural tube closure. Case and control
women were asked to recall corn consumption as
much as a year earlier. However, dietary recall
over a much longer period has been shown to be
generally reliable (Byers et al. 1987). Although
it might seem intuitive that case women were more
motivated to remember some events as they sought
explanations for having a child with a birth
defect, this has not proved to be a consistent
bias in studies comparing prospective and
retrospective measurement of exposures (Khoury et
al. 1994; Mackenzie and Lippman 1989). It seems
unlikely that an event as routine as eating corn
tortillas would have been differentially
recalled. Furthermore, recall bias would not
easily account for the consistent observation of
an inverted U-shaped relation between
questionnaire and laboratory-measured exposures.
Temporality of the blood sample collection is
also an important concern. The sa:so ratio
measures acute exposure to fumonisins, with
levels returning to normal when the exposure is
removed. In our sample, the sa:so ratio was
measured 5-6 weeks postpartum and would reflect
periconceptional levels at neural tube closure
only if study participants were exposed to
fumonisins at a constant level. We note, however,
that in rats and mice, a subtoxic fumonisin dose
will maintain elevated sphinganine when it
follows exposure to a higher dose (Enongene et
al. 2002; Wang et al. 1999). We have observed
that tortilla consumption varies little with
women's pregnancy status, making it possible that
this population is continuously exposed to some
level of fumonisins. In addition, the biochemical
mode of action gives no indication that this is a
case of reverse causation, that is, the NTD (due
to low folate or the shorter gestation) causing
elevated sa:so ratios in the mother (Gelineau-van Waes et al. 2005).
Our imputation of daily fumonisin consumption
also had several limitations. To provide an
estimate of fumonisin consumption from corn
tortillas, tortillas were collected from homes
and local grocery stores, which may or may not
indicate what was actually consumed by each
woman. In addition, the collection of corn
tortillas was not systematic, and the samples
were not proportionately representative of
region, brand, or season. Further, the daily dose
of fumonisin exposure depended on the number of
tortillas women recalled, which as we noted is
subject to error. Despite these limitations, it
is noteworthy that the estimated levels of
fumonisin ingestion for some women (650-9,441
ng/kg body weight for women in the highest
quartile) surpass the World Health Organization's
maximum tolerable daily intake of 2 痢/kg (2,000
ng/kg) of body weight of any combination of fumonisins (WHO 2002).
The higher proportion of refusals to participate
among control women (27%) compared with case
women (12%) is another potential concern.
Analyses conducted by Suarez et al. (2000)
validated that control women mirrored the
demographic characteristics of all border
Mexican-American women who gave birth during the
study years, indicating the low likelihood that
control women were seriously unrepresentative of the border population.
The evidence that fumonisins may play a role in
the development of NTDs is slowly being
assembled. Through our epidemiologic study, we
have documented that a population with a high
prevalence of NTDs also consumes large amounts of
corn products (tortillas). In addition, we have
demonstrated that the amount of fumonisins in
corn used to make tortillas may be high. We have
illustrated with laboratory data that, within a
certain range, women with increasing sa:so ratios
(a surrogate for fumonisin exposure) are
increasingly likely to have had an NTD-affected
pregnancy, independent of known NTD risk factors
(folate, B12, obesity, and other covariates).
Previous work shows that this population obtains
folate largely through diet and that the use of
folic acid-containing vitamins is rare. The
negligible effect of serum folate in the model
reflects this lack of supplementation (Suarez et
al. 2000). In fact, B12 levels are a more
important predictor of NTD risk than are folate
levels in this population (Suarez et al. 2003), a
risk factor included in the adjusted model for fumonisin exposure.
Recent laboratory experiments complement these
epidemiologic findings by illuminating the
biologic mechanisms through which fumonisins
might increase risk for NTDs. Fumonisins have
been shown to inhibit the biosynthesis of
sphingolipids (Wang et al. 1991), which
interferes with the uptake of
5-methyltetrahydrofolate and decreases total
folate binding (Stevens and Tang 1997).
Furthermore, mice embryos subjected to fumonisin
exposure develop NTDs in vitro (Flynn et al.
1997; Sadler et al. 2002) and in vivo
(Gelineau-van Waes et al. 2005). Administration
of folate reverses this effect (Gelineau-van Waes
et al. 2005; Sadler et al. 2002). Cumulatively,
these biologic and epidemiologic findings support
the hypothesis that fumonisin contamination of
corn destined for human consumption poses a risk
for NTDs through its impact on sphingolipid and,
ultimately, folate metabolism.
Based on our findings, it is possible that the
1990-1991 Cameron County NTD outbreak shared an
etiology with the ELEM epizootics that slightly
preceded it. The discovery of an association
between fumonisin exposure and NTDs may help to
clarify both the etiologies of unexplained NTD
outbreaks and the increased background prevalence
observed in some populations (Moore et al. 1997;
Mutchinick et al. 1999). In 2001, the FDA
recommended that an evaluation of the dietary
intake of corn products by specific population
groups (e.g., Texas Hispanics) and the levels of
fumonisins found in those corn products was
needed to fully assess the potential health risks
(U.S. FDA 2001). Future epidemiologic studies
should focus on measuring individual fumonisin
intake in specific high-risk populations and
assessing its impact not only on the developing
embryo but also on other outcomes such as
impaired fecundity or pregnancy loss.
[]
References
Burgoon JM, Selhub J, Nadeau M, Sadler TW. 2002.
Investigation of the effects of folate deficiency
on embryonic development through the
establishment of a folate deficient mouse model. Teratology 65:219-227.
Byers T, Marshall J, Anthony E, Fiedler R,
Zielezny M. 1987. The reliability of dietary
history from the distant past. Am J Epidemiol 125:999-1011.
De La Campa R, Miller JD, Hendricks K. 2004.
Fumonisin in tortillas produced in small-scale
facilities and effect of traditional masa
production methods on this mycotoxin. J Agric Food Chem 52:4432-4437.
Dombrink-Kurtzman MA, Dvorak TJ. 1999. Fumonisin
content in masa and tortillas from Mexico. J Agric Food Chem 47:622-627.
Enongene EN, Sharma RP, Bhandari N, Miller JD,
Meredith FI, Voss KA, et al. 2002. Persistence
and reversibility of the elevation in free
sphingoid bases induced by fumonisin inhibition
of ceramide synthase. Toxicol Sci 67: 173-181.
Floss JL, Casteel SW, Johnson GC, Rottinghaus GE,
Krause GF. 1994. Developmental toxicity in
hamsters of an aqueous extract of fusarium
moniliforme culture material containing known
quantities of fumonisin B1. Vet Human Toxicol 36:5-10.
Flynn TJ, Stack ME, Troy AL, Chirtel SJ. 1997.
Assessment of the embryotoxic potential of the
total hydrolysis product of fumonisin B1 using
cultured organogenesis-staged rat embryos. Food Chem Toxicol 35:1135-1141.
Gelineau-van Waes J, Starr L, Maddox J, Aleman F,
Voss KA, Wilberding J, et al. 2005. Maternal
fumonisin exposure and risk for neural tube
defects: mechanisms in an in vivo mouse model.
Birth Defects Res A Clin Mol Teratol 73:487-497.
Greenland S, Rothman KJ. 1998. Fundamentals of
epidemiologic data analysis. In: Modern
Epidemiology (Rothman KJ, Greenland S, eds). 2nd
ed. Philadelphia: Lippinicott-Raven, 205-207.
Gunter EW, Lewis BL, Koncikowski SM. 1996.
Laboratory methods used for the Third National
Health and Nutrition Examination Survey (NHANES
III), 1988-1994. Vol VII-D-1 to VII-D-12.
Hyattsville, MD:Centers for Disease Control and Prevention.
Hendricks K. 1999. Fumonisins and neural tube
defects in south Texas. Epidemiology 10:198-200.
Hendricks KA, Simpson JS, Larsen RD. 1999. Neural
tube defects along the Texas-Mexico border,
1993-1995. Am J Epidemiol 149:1119-1127.
Khoury MJ, James LM, Erickson JD. 1994. On the
use of affected controls to address recall bias
in case-control studies of birth defects. Teratology 49: 273-281.
Mackenzie SG, Lippman A. 1989. An investigation
of report bias in a case-control study of
pregnancy outcome. Am J Epidemiol 129:65-75.
Medicode, Inc. 1993. Med-Index International
Classification of Diseases 9th Revision Clinical
Modification. Vols 1 and 2. Fourth Edition. Salt
Lake City, UT: Med Index Publications.
Merrill AH, Sullards MC, Wang E, Voss KA, Riley
RT. 2001. Shingolipid metabolism: roles in signal
transduction and disruption by fumonisins.
Environ Health Perspect 109(suppl 2):283-289.
Moore CA, Li S, Li Z, Hong S, Gu H, Berry RJ, et
al. 1997. Elevated rates of severe neural tube
defects in a high-prevalence area in Northern
China. Am J Med Genet 73: 113-118.
Mutchinick OM, Lopez MA, Luna L, Waxman J,
Babinsky VE, and the RYVEMCE Collaborative Group.
1999. High prevalence of the thermolabile
methylenetetrahydrofolate reductase variant in
Mexico: a country with a very high prevalence of
neural tube defects. Mol Genet Metab 68: 461-467.
Reddy RV, Johnson G, Rottinghaus GE, Casteel SW,
Reddy CS. 1996. Developmental effects of
fumonisin B1 in mice. Mycopathologia 134:161-166.
Riley RT, Enongene E, Voss KA, Norred WP,
Meredith FI, Sharma RP, et al. 2001. Sphingolipid
perturbations as mechanisms for fumonisin
carcinogenesis. Environ Health Perspect 109(suppl 2):301-308.
Riley RT, Wang E, Merrill AH. 1994. Liquid
chromatographic determination of sphinganine and
sphingosine: use of the free
sphinganine-to-sphingosine ratio as a biomarker
for consumption of fumonisins. J Assoc Off Anal Chem Int 77: 533-540.
Ross PF, Rice LG, Osweiler GD, Nelson PE, Richard
JL, Wilson TM. 1992. A review and update of
animal toxicoses associated with
fumonisin-contaminated feeds and production of
fumonisins by Fusarium isolates. Mycopathologia 117:109-114.
Sadler TW, Merrill AH, Stevens VL, Sullards MC,
Wang E, Wang P. 2002. Prevention of fumonisin
B1-induced neural tube defects by folic acid. Teratology 66:169-176.
SAS Institute Inc. 1991. SAS/STAT Software: The
PHREG Procedure: Preliminary Documentation. Cary, NC:SAS Institute Inc.
Seifert KA, Takayuki A, Baayen RP, Brayford D,
Burgess LW, Chulze S, et al. 2003. The name
Fusarium moniliforme should no longer be used. Mycol Res 107:643-644.
Stack ME. 1998. Analysis of fumonisin B1 and its
hydrolysis product in tortillas. J AOAC Int 81: 737-740.
Stevens VL, Tang J. 1997. Fumonisin B1-induced
sphingolipid depletion inhibits vitamin uptake
via the glycosylphosphatidylinositol-anchored
folate receptor. J Biol Chem 272:18020-18025.
Suarez L, Hendricks KA, Cooper SP, Sweeney AM,
Hardy RJ, Larsen RD. 2000. Neural tube defects
among Mexican Americans living on the US-Mexico
border: effects of folic acid and dietary folate.
Am J Epidemiol 152: 1017-1023.
Suarez L, Hendricks K, Felkner M, Gunter E. 2003.
Maternal serum B12 levels and risk for neural
tube defects in a Texas-Mexico border population. Ann Epidemiol 13:81-88.
U.S. FDA. 2001. Background Paper in Support of
Fumonisin Levels in Corn and Corn Products
Intended for Human Consumption. Washington,
DC:U.S. Food and Drug Administration. Available
<http://www.cfsan.fda.gov/~dms/fumonbg3.html>http://www.cfsan.fda.gov/~dms/fumonbg3.html
[accessed 4 August 2005].
Wang E, Norred WP, Bacon CW, Riley RT, Merrill
AH. 1991. Inhibition of sphingolipid biosynthesis
by fumonisins. Implications for diseases
associated with Fusarium moniliforme. J Biol Chem 266:14486-14490.
Wang E, Riley RT, Meredith FI, Merrill AH. 1999.
Fumonisin B1 consumption by rats causes
reversible, dose-dependent increases in urinary
sphinganine and sphingosine. J Nutr 129:214-220.
Weinberg CR, Wilcox AJ. 1998. Reproductive
epidemiology. In: Modern Epidemiology (Rothman
KJ, Greenland S, eds). 2nd ed. Philadelphia:Lippincott-Raven, 585-608.
World Health Organization. 2002. Report on
Meetings of Expert Committees and Study
Groups--Evaluation of Certain Mycotoxins.
Geneva:World Health Organization. Available:
<http://www.who.int/gb/ebwha/pdf_files/EB110/eeb1106.pdf>http://www.who.int/gb/ebwha/pdf_files/EB110/eeb1106.pdf
[accessed 4 August 2005].
Yoshizawa T, Yamashita A, Luo Y. 1994. Fumonisin
occurrence in corn from high- and low-risk areas
for human esophageal cancer in China. Appl Environ Microbiol 60: 1626-1629.