Sons born to women who ate a lot of beef during their pregnancy have a 25 percent below-normal sperm count and three times the normal risk of fertility problems, researchers report.
The problem may be due to anabolic steroids used in the United States to fatten the cattle, Shanna H. Swan of the University of Rochester Medical Center reported in the current issue of the journal Human Reproduction. It could also be due to pesticides and other environmental contaminants, she said.
If the sperm deficit is related to the hormones in beef, Swan's findings may be "just the tip of the iceberg," biologist Frederick vom Saal of the University of Missouri wrote in an editorial accompanying the paper.
In daughters of the beef-eaters, those same hormones could alter the incidence of polycystic ovarian syndrome, the age of puberty, and the postnatal growth rate, vom Saal said.
"It's a small effect, but it is a significant effect," said Ted Schettler, an environmental-health specialist at the Institute for Global Communications in San Francisco. "It's not surprising. The more you look at dietary factors, the more you turn up interesting information about how diet during pregnancy affects . . . health."
Six growth-promoting hormones are routinely used in cattle production in the United States and Canada: the natural steroids estradiol, testosterone and progesterone, and the synthetic hormones zeranol, trenbolone acetate and melengestrol acetate. At slaughter, not all of these hormones have been metabolized.
Diethyl stilbestrol was also used in the United States between 1954 and 1979, when it was banned after tests showed that minks fed chicken waste containing DES became infertile.
The Food and Drug Administration sets limits on how much hormone residue is permissible in beef. Those limits may need to be reexamined if Swan's findings can be confirmed, vom Saal said.
The use of these hormones in beef was banned in Europe in 1988, and there has been an ongoing dispute about the EU's attempts to ban imports of U.S. beef containing hormones.
Studies in rodents have shown that even a tiny amount of estrogen present in the uterus from food can affect the sperm count of male offspring, but no one has previously attempted to study the question in humans.
For the latest research, Swan and her colleagues studied 387 partners of pregnant women in five U.S. cities. Each of the men provided a sperm sample, and their mothers filled out a questionnaire about their food consumption during pregnancy.
Swan concedes that women may have difficulty recalling their diets more than two decades earlier, but pregnancy may represent an exception. "When you are pregnant, are very aware of what you eat," she said.
The mothers were asked how often they ate beef and other meats. On average, they ate beef 41/2 times a week, and other meats much less frequently.
Researchers found that, in general, the more beef a woman ate, the lower her son's sperm count. For women who ate beef at least seven times a week, the son's sperm averaged 24 percent below normal. And even though those sons were successful in producing a pregnancy, they were three times as likely to have consulted a fertility doctor before doing so.
The researchers found no link to the mother's smoking, employment outside the home or the number of children she had. There was not enough data on meats other than beef to reveal a potential association.
The finding is only applicable to North American women, Swan said, because beef-growing practices vary around the world.