Low Sperm Count In American Men Linked To Their Mothers Eating A Lot Of Beef When Pregnant
The study is published in the journal Human Reproduction and was led by researchers at the University of Rochester in New York.
The intention of the study was to look at the relationship between semen quality and risks due to growth hormones and other chemicals in beef.
However, while the scientists found a strong correlation between mothers who ate beef at least seven times a week and sons with the lowest sperm counts, they could not pin this to specific hormones, pesticides or other chemicals that might have been used in the rearing of the beef cattle.
Professor of Obstetrics and Director of the Center for Reproductive Epidemiology at the University of Rochester Medical Center and lead author of the study, Dr Shanna H Swan said that the study's main contribution is that it raises an issue rather than identifies a cause.
Prof Swan said the team found that, "The average sperm concentration of the men in our study went down as their mothers' beef intake went up".
"But this needs to be followed carefully before we can draw any conclusions," she cautioned.
Although some of the 387 men in the study had low sperm counts, they had all conceived children without medical help.
But 18 per cent of the 51 men whose mothers had eaten the most beef while pregnant had sperm counts of 20 million per millilitre or less, which is classed by the World Health Organization (WHO) as "sub-fertile".
Men whose mothers ate less beef while pregnant had on average 24 per cent higher sperm counts, and only 5 per cent of them fell into the WHO's "sub-fertile" category.
Swan said the message to be taken from this research is that pregnant women eating a lot of beef could affect the development of sperm in male fetuses.
Although semen develops in three stages: before birth, during puberty and in adulthood, the period around the end of the third month of pregnancy is a critical time for quality semen to develop effectively in the male fetus said the study authors.
The researchers enrolled participants from the Study for Future Families (SFF), a multi-centre project supported by federal funds, including the National Institutes of Health, that gives scientists investigating links between environment and reproductive health access to a cohort of mothers, fathers and their children. Prof Swan has been the principal investigator of SFF since 1998.
The men were asked questions about their diet and gave sperm samples, and their mothers were asked questions about their diet, including frequency and type of meat consumption, when they were pregnant.
Sperm quality was assessed in a number of ways, for instance movement and concentration were two key indices.
The study found no correlation between the men's own beef intake and sperm quality.
The scientists found no significant links between maternal consumption of other types of food (pork, lamb, veal, chicken, soya and vegetables) and sperm quality.
The average number of beef meals per week consumed by the mothers was 4.3, and those who ate more than one meal of beef per day on average were classed a "high beef consumers".
The reason that the researchers used data from men born between 1949 and 1983 was because this was a period in the US when it would have been very difficult for most beef eating women to avoid eating meat from cattle reared using hormones and other chemical additives.
There are many explanations for the results of this study, and the authors are keen to stress that it was not designed to pinpoint causes.
However, it is possible that chemical contaminants, pesticides and hormones in the beef could be the reason for these results. But so could a range of lifestyle factors. And asking mothers to remember how often they ate meat 20 to 50 years ago is not exactly watertight science, despite the fact that pregnancy is a time when women probably have better awareness of their diet, acknowledged the researchers.
Prof Swan concluded that the study should be replicated to confirm the findings, and suggests that one way to "determine if prenatal exposure to anabolic steroids is responsible for a change in sperm count would be to repeat this study in men born in Europe after 1988, when hormones were no longer permitted in beef sold or produced there".
The researchers said this study does not qualify them to advise women on how much beef they should eat, but perhaps very high consumption should be avoided.
"Semen quality of fertile US males in relation to their mothers' beef consumption during pregnancy."
S H Swan, F Liu, J W Overstreet, C Brazil, and N E Skakkebaek.
Hum. Reprod. Advance Access published on March 28, 2007.
Click here for Abstract.
Click here for What to Eat When Pregnant (Food Standards Agency, UK).
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