A recent study has identified a possible relationship between sperm counts in men and their mother's consumption of beef during pregnancy. Of particular concern was whether administering hormones to cattle to increase their size and beef production could be the culprit leading to these findings.

Hormone supplementation in cattle

Diethylstilbestrol (DES) is a synthetic estrogen, which was first formulated in 1933. Most obstetricians are familiar with DES since it was found that women who were given DES during pregnancy to help prevent miscarriage, subsequently delivered daughters with uterine abnormalities and who had a higher risk of vaginal cancer. In 1947, the year that DES was approved for use by pregnant women, investigators at Purdue University demonstrated the ability of DES to stimulate growth in cattle.

Although DES is no longer used in cattle, the use of other hormones continues to be used legally in the USA and elsewhere as growth promoters in meat production. Six hormones are now in common use in Canada and USA: the three natural hormones: estradiol, testosterone and progesterone, and the three synthetic hormones: zeranol (an estrogen), trenbolone acetate (a steroid with androgen and glucocorticoid action) and melengestrol acetate (a potent progestin). These hormones are often used in combinations.

At slaughter, measurable hormone levels are present in muscle, fat, liver, kidney and other organs present in meat products. Therefore, it has been necessary to regulate the use of these growth promoters to avoid unintended adverse effects in humans eating these meat products. The FDA has defined an ‘acceptable daily intake’ (ADI) for each of these hormones. Interestingly, the use of these hormones has been banned in Europe since 1988.

Despite these regulations, the consumption of trace amounts of hormones in meat by pregnant women and young children is of particular concern. Recent animal and human studies have suggested that exposure to these hormones during pregnancy and shortly after delivery may have an affect on the adult male testicle and may have an adverse effect on sperm production.

Men and their mothers were studied

A large multi-center study of pregnant women and their partners was conducted at medical centers in 5 major American cities between 1999 and 2005. Both male and female partners completed a questionnaire and most men provided a semen sample. Questions for the men included other factors that are relevant for sperm production such as a recent fever, history of sexually transmitted diseases, as well as lifestyle factors (smoking, alcohol and caffeine consumption) and diet (including number of servings of beef and other red meat). The men were also asked, ‘Have you ever seen a doctor because you thought you might be having trouble fathering a child’.

Each man was also asked to have his mother to complete a brief questionnaire. The mother's questionnaire asked, ‘In a typical week while you were pregnant with your son —, did any of your meals contain the following foods?’ Separate questions on beef, lamb or pork, veal, etc. followed. If the mother responded "yes", she was asked to specify the number of meals per week that included that food item.

Ultimately, 514 men were studied. In each of these men, a semen sample was obtained and their mother provided a questionnaire which included information on the number of beef meals consumed during pregnancy.

Sperm numbers lower in sons of "high" beef eaters

Mothers consumed, on average, 4.3 beef meals per week (range 0–21) and only 15 (4%) reported eating no beef during pregnancy. The number of beef meals consumed by the mother was related to her son's sperm concentration. The more beef a mother ate during pregnancy, the lower her son's adult sperm concentration.

The average sperm concentration among sons of ‘high beef’ eaters was 43 million sperm per m L. For those whose mothers were not high beef eaters it was 24.3% higher (57 million sperm per m L). Among sons of mothers whose beef consumption was lower, only 5.7% had a sperm concentration low enough to be considered "subfertile". For women who admitted high beef consumption, 17.7% had a subfertile sperm concentration. The number of men who sought a doctor's care for concern about their fertility was almost twice as high in the sons of women who ate larger amounts of beef (9.8% compared to 5.7%) Statistical analysis determined that these differences were unlikely to be due to chance. A somewhat weaker relationship was found between the types of beef eaten (red meat versus other).

The mother's consumption of fish, chicken, soy products and vegetables was not related to sperm concentration. Sperm motility (the percentage of moving sperm) and morphology (the percentage of sperm with a normal appearance under the microscope) were not related to mother's beef consumption.

Important limitations of this study to be aware of

It is important to point out several important factors in this study. First, these studies relied on the recollections of women going back two decades or more. It is always possible that the recollections are not accurate and this could significantly affect the results of the study. Second, the vast majority of mother in this study lived in North America. These relationships may not hold up in other countries. Third, although differences in sperm concentrations were found, all of the men had pregnancies with their partners that were conceived without medical assistance. It is not known whether beef consumption by mothers during pregnancy is an actual risk factor for infertility.

The study cannot say with certainty that hormone levels within the beef consumed were the actual cause of the lowered sperm counts. It is possible that some other beef contaminant (such as pesticides) was responsible or some other lifestyle difference commonly seen in beef eaters was the real culprit.