This week researchers from the University of Bristol announced that their study of 8,000 infants found that babies born to vegetarians were up to five times as likely to suffer from some forms of birth defects. But how reliable is this?
This is not the first Bristol study to tie birth defects to vegetarianism. In 1999, Bristol researchers announced a study finding that boys born to vegetarian mothers were five times as likely to suffer from hypospadias, a condition where the opening of uretha occurs at a point below the tip of the penis.
Another study, conducted at Nottingham University, found that whereas the average sex ratio of children born in Great Britain was 106 boys to every 100 girls, in vegetarian women the ratio was only 85 boys to every 100 girls. That study was widely criticized since it is sperm from the male that determines the sex of the child, though the researcher suggested that a vegetarian diet might somehow alter body chemistry to favor sperm carrying DNA for a female (if there is really a connection between vegetarianism and the sex of children, a much likelier explanation is that children born to vegetarian mothers are almost certainly much more likelier to have vegetarian fathers as well).
A major problem with all three of the studies mentioned above is that none of them appears to have been peer reviewed in a serious research journal. The sex ratio research, for example, was published in Practising Midwife. Now, this is probably an excellent journal for what it does, but The Lancet it is not.
Another major problem is that news accounts of these studies never report on the sample size for vegetarians and non-vegetarians. Typically a study of both groups will tend to include far more non-vegetarians than vegetarians, significantly reducing the usefulness of the results. If 4,000 of the babies in the Bristol study had vegetarian mothers, the results are far more interesting than if the study was more like 7,500 non-vegetarians and 500 vegetarians.
The culprit that the researchers finger in all three cases is soya, which is a major source of protein in many vegetarian diets. Animal studies suggest that high consumption of soya exposes mammals to very high levels of estrogen-like compounds, but if soya is really a major problem, then why has soya been eaten regularly by hundreds of millions of people for decades without anyone noticing this before?
What is really needed to resolve this is a well-designed study subjected to peer review. Until then, call me skeptical.
Source:
Vegetarian diet linked to genital defects. Matthew Hill, The BBC, July 2, 1999.
Vegetarian Diet In Pregnancy Linked To Birth Defect. BJU International January 2000;85:107-113.
‘More girl babies’ for vegetarians. The BBC, August 7, 2000.
Meat-free diet puts infants at risk. Europe Intelligence Wire, July 10, 2002.