04 September 2006
ByAppeared in BioNews 374
A man's infertility could be directly linked to his body weight, a current American-based study reveals. Data from the National Institute of Environmental Health Sciences (NIEHS) suggests that overweight men are significantly more likely to be infertile than normal-weight men, and that for every 20-pound body weight gain in men there is a ten per cent increase in infertility.
The study took place in rural Iowa and North Carolina, where the researchers looked into the fertility levels of around 2000 couples, of whom the men were mostly farmers and the wives were all under forty years old. The men's weight statuses were determined by calculating their body mass index (BMI), a value which relates height to weight, where normal-weight men have a BMI of 20-25.9 and overweight men have a value of 26 plus. The wives were then asked about the couple's reproductive history and any infertility, defined by the study as when no pregnancies occurred in 12 months of unprotected sex during the four-year research period, even if the wives became pregnant after this time slot.
Contributing factors that could interfere with fertility, such as the wives' BMI, smoking, alcohol use and exposure to solvents or pesticides, were accounted for by the researchers. But they did not record how frequently the couples had sex, so they cannot be certain that a man's sperm is affected by his weight, as the study's overweight men may have been having sex less often than the normal weight men. The research also does not look into whether a changing BMI over time affects fertility levels in men.
'To our knowledge, this was the first study to examine male BMI and couple fertility. Thus, it is important that the findings will be confirmed or refuted in future studies', said researcher Markku Sallmen, before adding that the findings 'must be viewed as supportive but not confirmatory of an association, given the limitations of the study data'.
If this study is supported by more studies on male fertility, it is likely that infertility in men could be yet another health problem associated with rising obesity levels in industrialised countries.