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“Fertility problems seen for sons of beef-eating women,” announced the San Francisco Chronicle, to the widespread dismay, no doubt, of the beef-eating mothers of America (thanks to similar stories The Baltimore Sun, The Philadelphia Inquirer and Medicine.net). The news was driven by a new theory about male fertility, which suggests that if a mom consumes too much beef while pregnant, her son will suffer when it comes to being fruitful and multiplying. But in typical form, journalists were having a cow over research that didn’t say what they thought it said. In a new study that appeared in the March 28 edition of Human Reproduction, authors Shanna Swan et al. explore the thesis that increased beef consumption is correlated with decreased sperm counts, decreased percentage of motile (moving) sperm or abnormal morphology (shape) of sperm. They found that while the percentage of motile sperm and the percentage of sperm with normal morphology were not affected by beef consumption, the concentration of sperm was lower among higher beef consumers. But the lower sperm count did not cause reduced fertility. The men participating in the study were the fertile partners of pregnant women participating in a large multi-center pregnancy cohort study called the Study for Future Families. Those who got pregnant through any kind of fertility treatment were excluded from the study. The study was in no way designed to evaluate fertility as distinct from sperm count. Strangely, this fact, evidenced in the title of the paper, was correlated with headlines suggesting exactly the opposite. While it is true that reduced sperm count can affect fertility, the real issue is how low the sperm count goes. It turns out that the reduction in sperm count noticed by Swan’s research group is comparable to that attributed to aging. In a 2003 study that appeared in the same journal, B. Eskenazi et. al. found that sperm count goes down significantly with age from men in their twenties to men in their thirties. On average, these men see a reduction of 22 percent over this period. This figure is similar to the 24 percent reduction of sperm count in men whose mothers consumed eight or more meals a week of beef, compared to those whose mothers consumed less. So why isn’t the press warning us about the dangers of men waiting until their thirties to try to have children? Is beef the problem, or is it something else? As the study acknowledges, it can only get at this information indirectly. Most beef consumed at the time that the mothers of these men were pregnant had trace elements of hormones in them, though the quantity was regulated by the FDA. Unfortunately, even if eating beef is really the reason behind a lower sperm count, there is no way to be sure that the cause is growth hormones or some other feature of beef. And in terms of public policy, the situation is even more complicated, because one growth hormone is no longer in use: diethylstilbestrol (DES) was discontinued in 1979, while other hormones continue to be widely used. However, even the claim that beef is the main reason behind the observed correlation between beef and sperm count is potentially suspect. Most relevant is the issue of confounding factors, or information that may not have been considered that may have a big impact on how the statistics are interpreted. In the case of this particular study, there are some important questions that arise. Were the mothers exposed to other toxins that could be related to beef consumption, such as pesticides or other substances? If women who ate more beef were also more likely to live near other toxins, one might see an effect from beef that’s actually attributable to environmental factors. And these environmental factors could even be influencing the boys throughout their childhood, rather than just in utero. This point is particularly worrisome because of the high correlation between beef eating patterns, and the country in which the kids were born. Men whose mothers consumed a lot of meat were much less likely to be born in a foreign country than men whose mothers consumed less. This means that a whole range of factors influencing sperm count could come into play – perhaps Americans are more stressed than non-Americans. Perhaps there are a different set of pollutants, or other differences in eating patterns or vitamin consumption. The results would have to be put in the context of other observable differences between mothers who are gestating in the U.S. and mothers who are not. There are other differences between the two groups that were noticed, but remain unaddressed. For example, alcohol consumption was up among the sons of low-beef eaters – the difference is not quite statistically significant, but it is borderline (p=.053). It is possible that there is a relationship between alcohol and sperm count? Could alcohol actually promote sperm production? Unfortunately the study doesn’t address this. Overall, the study indicates that there is a possibility that beef consumption has an impact on sperm count, though not on sperm motility or morphology. Whether this impact is due to growth hormones used in the United States could in part be evaluated by doing a study in Europe where these hormones have been banned. For right now, we should be skeptical of results suggesting an impact on fertility, and even more suspect of the conclusion that the hormones are the problem. All this remains to be seen; in the meantime, relax; these men are having kids.
Eating Beef Harms Fertility – A Cock and Bull Story?
Are “the sons of beef-eating women” in danger?
The article is actually attempting to evaluate the possibility that there are long-term risks to semen quality in men who have been exposed in utero to beef containing steroids or other hormones.
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