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Is there any evidence to suggest that cycling adversely affects male fertility?

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I don't think that cycling has affected the fertility of the Chinese or the Indians. That's a research sample of some two billion people for you... –  ʍǝɥʇɐɯ Jul 28 '11 at 10:23
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Well, probably yes. But these are guys who shave their legs -- is fertility the top thing on their mind? ;) –  Daniel R Hicks Jul 28 '11 at 11:06
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2 Answers 2

Most scientific studies on cycling and urogenital problems are written with clinicians in mind, to make them aware of possible symptoms that they will encounter. Often these studies get summarized into review articles. One such article (Leibovitch and Mor, 2005), reviewed 62 relevant studies. They say:

The reported incidence of bicycling related urogenital symptoms varies considerably. The most common bicycling associated urogenital problems are nerve entrapment syndromes presenting as genitalia numbness, which is reported in 50–91% of the cyclists, followed by erectile dysfunction reported in 13–24%. Other less common symptoms include priapism, penile thrombosis, infertility, hematuria, torsion of spermatic cord, prostatitis, perineal nodular induration and elevated serum PSA, which are reported only sporadically.

When examined individually, many of these studies have limitations (small number of study subjects, no followup, etc.), but when taken as a whole, they are pretty conclusive that an association exists between cycling and urogenital problems.

The only study that I could find that was population-based, i.e., included men with a range of cycling durations, was Marceau et al., 2001. Their data on 1,709 men come from the Massachusetts Male Aging Study. After controlling for potentially confounding factors ("age, energy expenditure, smoking, depression and chronic illness"), they found that men who cycled more than 3 hours per week were 72% more likely to have erectile disfunction than those who cycled less than 3 hours per week. They are cautious, however (emphasis mine):

Bicycling 3 h or more per week may be associated with ED. Data revealed that there may be a reduced probability of ED in those who ride less than 3 h per week and ED may be more likely in bikers who ride more than 3 h per week. More population-based research is needed to better define this relationship.

The last sentence is key. Granted, there are drawbacks to population-based studies like this. One major problem is that the data are self-reported. Another drawback is they their sample probably does not include elite or high-level sport cyclists, who might have better equipment or better technique.

Does this mean that your experience may vary? Absolutely.

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There a are a lot of variable when considering personal health, and a lot of serious sounding articles drawing "correlations" that seem to conflict with similar studies regularly--for many health and nutrition topics. Personal body types and capabilities vary so much that studies like these have to offer predictable conclusions before civilians should pay attention to them. ED might also be a side effect of unrelated blood pressure medications, for example. –  memnoch_proxy Aug 6 '11 at 7:00
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Yes, but only in fairly extreme cases.

According to this article, cyclists who regularly cover more than 186 miles (300km) per week are likely to have fertility problems.

If you're not doing that kind of mileage then I don't think you've got too much to worry about.

Edit:

I've just found this essay - Great balls of fire and the vicious cycle: A study of the effects of cycling on male fertility

According to this essay there is some evidence that cycling long distances can cause fertility problems in men, however it is far from conclusive. Nerve entrapment, trauma or increased scrotal temperature are potential risks for the male cyclist.

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It's not cycling specific either. Appears to be observed with all types of athletes. –  Brian Knoblauch Jul 28 '11 at 12:26
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186mi/wk is considered to be extreme? Shit. –  Stephen Touset Jul 28 '11 at 13:11
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My understanding was that the issue for the average rider with poor equipment was more a possibility residual numbness and "failure to operate" than infertility. Is that what you are discussing, or is this a separate topic? –  zenbike Jul 28 '11 at 14:01
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I disagree that 186 mi/wk should be viewed as some kind of cutoff. I read the original article that is described in the BBC news report. 330 km/wk is the average mileage of the triathletes in the study cited above. The did not perform any kind of regression of sperm concentration on mileage, so there is no way to know if sperm concentration decreases linearly with mileage or if any type of cutoff exists. –  kmm Jul 28 '11 at 15:01
    
What if you wish you were doing 300K a week? :) –  geoffc Jul 28 '11 at 18:53
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