paper establishes a statistically significant association between
maternal diet and subsequent hypospadias in boys born to vegetarian
mothers. Hypospadias is a structural defect in the penis that has
been increasing in frequency in several countries over the past
20 years, including the United States [More...]
important aspect of this study is that it was prospective. Mothers
were interviewed during pregnancy and thus the study avoids the
problem of biased recall. The study examined 7928 boys, of whom
51 had hypospadias.
vegetarian mothers, 2.2% gave birth to a boy with hypospadias, compared
to 0.6% of mothers who were omnivores. The adjusted odds ratio of
hypospadias for vegetarian mothers was 4.99 (with 95% confidence
intervals from 2.10-11.88).
et al. consider three possibilities for the association with
vegetarianism. One is the likelihood that vegetarianism will result
in increased intake of phytoestrogens, particularly in soy products.
A second is that an increased vegetable diet may expose the mother
to more pesticide residues. They are unable to resolve this with
the data they gathered because the sample of vegetarian mothers
who bought only organic food was too small. The authors note in
passing that none of these mothers (163 in total) gave birth to
a hypospadiac, but that only one would have been expected based
on the overall rate in the population. A third hypothesis is that
the vegetarian diet is more likely to lack some nutrient essential
for male reproductive tract development.
authors refer to the higher use of soy in the Japanese diet, but
make no reference to data
indicating that the rate of hypospadias in Japan is less than one-tenth
the overall rate reported in this study. This apparent conflict
with their "soy hypothesis" might reflect metabolic differences
among populations, given that soy has been part of the traditional
diet in Japan for many generations.
study controls for a wide variety of variables that might confound
the relationship. They did take blood samples and expect to measure
levels of phytoestrogens, pesticide residues and essential nutrients
in a later study. This may allow a more definitive test of the three
authors also noted an association with iron tablets: 1% of mothers
who had taken iron tablets during pregnancy had boys born with hypospadias,
a statistically significant finding compared to omnivorous mothers
who had not taken iron (0.6%). Because iron supplements are common
in vegetarian diets, North et al. examined this more closely.
They found that vegetarian mothers who did not take iron were more
likely to have hypospadias, and that non-vegetarian mothers who
took iron were also more likely to give birth to boys with hypospadias.