Bad news for guys who like to bike. A study out from Boston University has found that bicycling for five or more hours a week may be associated with low sperm count and poor sperm motility, two factors that affect male fertility. Published online December 3, 2010, in the journal Fertility and Sterility, the study surveyed 2,200 men attending fertility clinics in the Boston area between 1993 and 2003. Researchers asked the men details about their exercise levels, type of exercise, general health, and medical history. Each man also provided at least one semen sample.
Overall, researchers found that exercise levels generally had very little overall impact on sperm quality and quantity. But when specific forms of exercise were looked at, researchers note that men who bicycled for at least five hours a week were more likely to have a low sperm count and fewer motile sperm (sperm that can "swim" well) than men who did not exercise at all, or those who took part in other forms of exercise. As the study turns up, less than a quarter of the non-exercisers had a low sperm count, compared to 31 percent of the frequent bike riders.
Studies of competitive cyclists have linked the sport to poor semen quality, but this is the first study to show that even average amounts of bike riding may put male fertility at risk. Lead researcher Lauren Wise speculated that semen may be affected by temperature increases in the scrotum or trauma while cycling. But she also noted that since the men were attending fertility clinics, it is unclear without further research, whether the findings would also hold true for men with otherwise healthy semen quality and fertility.