NEW YORK (Reuters Health) - Obese men are more than three times as likely to have low sperm counts compared with their normal-weight peers, a study out this month in the journal Fertility and Sterility shows.

The heaviest men were also at triple the risk of having a low count of progressively motile sperm -- sperm that swim forward in a straight line, Dr. Ahmad O. Hammoud of the University of Utah in Salt Lake City and colleagues found.

"There is a strong relationship between overweight and obesity and altered sperm parameters," Hammoud and his team write. Future studies should look at this relationship over time, they say, as well as how weight loss might affect sperm characteristics.

There has been some evidence that obesity may impair fertility in men, the researchers note, while increased body fat can contribute to lower testosterone levels and higher estrogen levels. To examine how body mass index (BMI) affects sperm quality, they evaluated 390 men who sought infertility treatment with their partners over a 2-year period.

Twenty-four percent of the men were normal weight, 43 percent were overweight, and 33 percent were obese. Overall, 10.5 percent had low sperm counts.

The prevalence of low sperm counts rose as BMI increased; obese men were 3.3 times more likely to have low sperm counts than normal-weight men. The risk of having a low count of progressively mobile sperm also rose with BMI; obese men were 3.4 times more likely than normal-weight men to have a low progressively mobile sperm count. Obese men were also 1.6 times more likely than overweight or normal-weight men to have a high percentage of abnormally shaped sperm.

While there was a trend toward increasing likelihood of erectile dysfunction with increasing BMI, the relationship wasn't statistically significant. However, the researchers note, other studies have found that obesity is associated with a greater risk of impotence.

The fact that the study was done among men seeking infertility treatment makes it likely that the study group had worse sperm quality than the population at large, Hammoud and colleagues point out. Nevertheless, they add, the correlation of poor sperm quality and increased BMI in the general population is probably similar.

SOURCE: Fertility and Sterility, December 2008.

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