She looks at me earnestly, searching for approval and says: “I’ve made sure that he stopped bicycling as I have read that it’s bad for his fertility, right?” Not so fast.
Sperm and Saddles
Research in this area has looked at both semen quality and fertility in relation to cycling activity. The whole issue surfaced recently with a Spanish study of elite triathletes, some of the most fit men on the planet. By examining only semen quality and not fertility, they concluded that those who cover more than 186 miles (300km) a week on bikes have sperm that is less “normal looking.” So, in men training 9 times a week for at least 8 years, sperm shape or morphology wasn’t perfect. Gees, give them a break! There must be 55 other issues that affect sperm shape, and this feature of sperm may have little to do with natural fertility. What also gives me pause is that this study was never formally published.
More relevant for the casual or commuting cyclist was a 10-year observational study from Boston that examined sperm counts in men from all walks of life. Among 2,261 men, 4,500 sperm samples were examined. Men who bicycled more than 5 hours per week had a 90% lower sperm concentration than men who did not exercise. Funny thing is, when looking at other variables known to be associated with impaired semen quality such as age and obesity, there were no associations found. Other weaknesses are that all men in the study were infertile with partners undergoing IVF treatment, which certainly complicates the picture and, again, fertility was not examined.
Bicycles and Babies
In fact, studies that actually examine fertility among cyclists, the most relevant outcome for this discussion, are vanishingly rare. Notably, the largest study to date (5200 British cyclists) and the most recent did just that. Lo and behold, there was no link between fertility and cycling up to 8 1/2 hours a week, the maximum bike time examined. Not only that, it appeared that cycling between 4 to 6 hours/week reduced the odds of being infertile by at least half.
And so it goes. The ying and yang of science. My advice: Take the usual precautions, but bicycle on. What a great way to exercise, improve health, cut stress and see the world.