It is known that obesity impacts fertility in women. The link between obesity, insulin resistance, and polycystic ovary syndrome (PCOS) is one example. According to an online report from the National Institute of Health (NIH), a new study, published in the September 2006 issue of journal Epidemiology suggests that men, too, may have more problems with infertility than men who are normal weight.

The research, led by Markku Sallmen and funded by the NIH’s National Institute of Environmental Health Sciences (NIEHS), analyzed data from questionnaires completed by 1,468 farmers and their wives. The research is a part of an ongoing study started in 1993 called the Agricultural Health Study. That study examines factors that relate to the health of farmers and their families in agricultural communities

The wives completed a family health questionnaire, which included information about the couple’s reproductive history. The men reported their weight and height on a questionnaire about their health. This allowed the researchers to calculate the men’s Body Mass Index (BMI), a measure of overweight or obesity.

The analysis was limited to couples that reported that they had tried to get pregnant in the four years before enrollment in the study. It was also limited to couples in which the woman was under the age of 40. The majority of participants were more than 30 years old.

The researchers divided the couples into infertile and fertile groups, defined as follows:

  • Fertile couples were those that conceived within a year
  • Infertile couples were those that tried for longer than a year to conceive


What did they find?

Using these definitions, the researchers found that 28% of the couples had experienced infertility. They also found that men’s BMI was an independent risk factor for fertility in both older and younger men. Even after adjustment for other factors that could affect fertility (high BMI of the woman, age, cigarette smoking, alcohol intake, and solvent and pesticide exposure), the researchers found that there was a general increase in infertility with increased BMI, reaching a nearly 2-fold increase among obese men.

The data suggest that a 20-pound increase in men’s weight may increase the chance of infertility by about 10 percent,” says Markku Sallmen, lead author on the paper who is now at the Finnish Institute of Occupational Health.

The researchers did not have data on frequency of sexual intercourse, so it is possible that overweight men have less sexual intercourse than their normal weight counterparts and this could influence fertility. However, there have been recent studies looking at semen characteristics that show lower semen quality for overweight and obese men, as well as hormonal differences.


The takeaway

It is important to point out that this study is an epidemiologic study and therefore can only suggest, not prove, a causal link between obesity and male infertility. It, nevertheless, adds to a growing body of scientific literature that documents adverse impacts of overweight and obesity on health. Further research is needed to determine if the relationship between obesity and male infertility is real and whether it occurs in all men or only in some men who may have a genetic predisposition, such as a relative insensitivity to insulin, to become infertile when they gain weight.