ROCHESTER, N.Y., March 28 -- Consumption of beef by women during pregnancy may alter a male's in utero testicular development and compromise his future reproductive capacity, researchers here reported.
The reason could be residual anabolic steroids in the meat, Shanna Swan, Ph.D., of the University of Rochester (N.Y.), and colleagues, reported online in the March 28 issue of Human Reproduction.
In a study of 387 fertile partners of pregnant women, men whose mothers reported eating more than seven beef meals a week while pregnant, had a sperm concentration more than 24% lower than that of men whose mothers ate less beef, they found.
In addition, three times more sons of high-beef consumers had a sperm concentration that would be classified as subfertile according to World Health Organization standards, compared with men whose mothers ate less beef, said Dr. Swan and colleagues.
Although the U.S. banned the growth promoter diethylstilbestrol (DES) for use in cattle in 1954, other hormones such as estradiol, testosterone, progesterone, and the synthetic hormones zeranol, trenbolone acetate, and melengestrol continue to be used, Dr. Swan said.
Because residues of the chemicals persist after slaughter, the FDA has regulated their use, defined as "acceptable daily intake." In Europe, the use of these natural and synthetic hormones has been banned since 1988.
"These acceptable daily intake are based on traditional toxicological testing, and the possible effects on human populations exposed to residues of anabolic sex hormones through meat consumption have never, to our knowledge, been studied," Dr. Swan and colleagues said. Therefore, she added, the consumption of meat by pregnant women and children is of particular concern.
The study was conducted in five U.S. cities between 1999 and 2005 and used the mothers' accounts of the amount of beef they ate. Sperm concentration was inversely related to the mothers' beef meals per week (P = 0.041), the researchers reported.
In sons of high beef eaters (more than seven beef meals a week), sperm concentration was 24.3% lower (P=0.014). Sons of high-beef consumers had an average sperm concentration of 43.1 million sperm/ml seminal fluid, while sons of mothers who ate less beef had an average of 56.9 million sperm.
The proportion of men with sperm concentrations below the WHO threshold of subfertility (20 x 106/ml) was three times higher (17.7% versus 5.7%, P=0.002) than in men whose mothers ate less beef.
A history of previous subfertility was also more frequent among sons of high beef consumers (P = 0.015), the researchers reported.
Sperm concentration was not significantly related to the mothers' consumption of other meats (pork, lamb, veal) or to the men's consumption of any meat, the researchers found. Also, mothers' consumption of chicken, fish, soy products, and vegetables appeared harmless.
On average, mothers ate 4.3 beef meals a week, and only 15 (4%) reported eating no beef during pregnancy, while 336 ate seven or fewer meals a week, and 51 reported eating more than seven beef meals a week, the researchers reported.
Women who ate large amounts of beef also ate significantly more red meat and were more likely to have lived in North America at the time their son was born than women who reported eating less beef.
However, the researchers pointed out that most mothers in this study lived in North American, and the findings may not apply to other regions of the world where beef is produced by other methods.
The researchers also noted that they could not rule out unknown confounders associated with the findings. For example, they said, pesticides, other contaminants in animal feed, and lifestyle factors correlated with greater beef consumption may play a role in the effect observed.
Also, they said, heterocyclic amines, produced in cooling and processing red meat, which are estrogenic, may also be involved.
"Whether prenatal exposure to anabolic steroids is responsible for our findings in whole of in part could be clarified by repeating this study in men born in Europe after 1988 when anabolic steroids were no longer permitted in beef or produced there," Dr. Swan's team concluded.