If you want longevity for your family tree, check what's on your plate. New research finds that pregnant women who eat beef seven days a week or more daily may give birth to sons with low sperm counts.

The exact reason for the association isn't clear. But hormones, pesticides or other chemicals in beef might affect the development of the testes of the still-developing fetus, say researchers.

"We're not saying that people should stop eating beef, and it's particularly important in pregnancy that women get enough protein," says study lead Shanna Swan of the University of Rochester School of Medicine and Dentistry. "Women have to eat protein, although they don't necessarily have to eat meat.

Alternatively, opting for hormone-free or organic beef during pregnancy—or reducing overall meat consumption—may also side-step potential low sperm counts in offspring, Swan adds.

The Study

For this study, the first one to examine beef consumption and semen quality, researchers analyzed semen samples and questionnaires from 387 male partners of pregnant women. The men, born between 1949 and 1983, had reported (with the help of relatives when possible) on their own mothers' diet during pregnancy.

Sperm concentration was inversely related to how much beef the mother had consumed each week. Sons of women who ate more than seven beef meals a week had sperm concentrations 24% lower than those whose moms ate less beef.

Overall, low sperm concentrations were three times higher among sons of women who consumed more than seven meals of beef a week, compared with men whose mothers ate less beef while pregnant. This pattern was only seen in beef-not veal, pork, fish or chicken, say researchers.

None of the men studied were infertile, but about one in five whose mothers ate the most beef had sperm counts classified as "sub-fertile" by national standards.

"They may have taken a longer time to conceive," says Swan. "They were twice as likely to have visited a doctor because they thought there were problems, so it's not to say there's no effect on fertility.

What To Blame?

The study authors can't say that anabolic hormones in beef are to blame. Most American cattle were given anabolic hormones to stimulate growth and the hormone residues were present in the beef consumed while these women were pregnant. Beef also contains residues of pesticides and other industrial chemicals.

Currently, six different anabolic hormones are used in cattle in the US and Canada to stimulate growth. Three are natural hormones-estradiol, progesterone and testosterone—and three are synthetic hormones-zeranol (an estrogen), trenbolone acetate (a steroid with androgen effects) and melengestrol acetate (a progestin), say researchers.

The use of these hormones has been banned in Europe since 1988.

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