Ejaculation and prostate cancer

There are many articles recommending men to have more ejaculations,  because of a study relating sexual activity to decreased chance of prostate cancer.

Some articles try to paint a more balanced view by looking at multiple sources of evidence. One of them is "Does Sex Increase Risk of Prostate Cancer?" from psychologytoday.com. They start by quoting 3 studies that actually indicate more sex is associated with higher risk of prostate cancer:

• Italian researchers: compared with men who never married, those who did--and presumably had more sex--had significantly greater risk of prostate cancer. 
•  University of Illinois: the younger the men became sexually active, the greater their risk. And the more sex partners they reported, once again, the greater their risk.
• University of Iowa researchers found that as number of women sex partners increased, so did risk of prostate cancer, with men who reported sex more than three times a week showing the greatest risk.

But then they turn to the study everyone else is quoting which apparently shows the opposite: more ejaculations decrease your risk of prostate cancer. But is that really the case if we read the study more carefully?


The odd study

The widely cited study which looked at the connection between ejaculatory frequency and prostate cancer risk is "Ejaculation frequency and subsequent risk of prostate cancer" by Leitzmann et al.

The study has been conducted on 29 thousand US men aged 46 to 81 years. Ejaculation frequency was assessed by asking participants to report the average number of ejaculations they had per month during the ages of 20 to 29 years, 40 to 49 years, and during the past year.

Results

There was a decreased risk of prostate cancer observed for men with high ejaculatory frequency in their 20s.

One important problem is how accurately can one remember it's ejaculation frequency in his 20's if asked when he's 50 or even 80 (20 to 50 years latter!), and the authors acknowledge this.

Nonetheless, assuming the data was accurate, this result only says that a pre-existent cancer risk may be lowered by more frequent ejaculations, which does NOT imply that abstinence would cause cancer. As obvious as that may sound, some people actually understood that  men need to have frequent ejaculations otherwise they would get cancer!

The twist

More interestingly, the same study says:

We noted a suggestive decrease in risk of total and organ-confined prostate cancer among men in the lowest category of ejaculation frequency across a lifetime. The apparent decrease in risk of total and organ-confined prostate cancer among men with a low ejaculation frequency was not due to low prevalence of sexually transmitted infections among these men because adjustment for history of syphilis or gonorrhea did not alter the results.

These results are actually consistent with the other quoted at the top, which suggests that the data for ejaculation frequency which men had between 20 and 29 years old may have been biased.

Conclusions

The study quoted by most people when they recommend increased sexual activity to reduce risk of prostate cancer, actually only found a decreased risk of prostate cancer for men with high ejaculatory frequency in their 20s. The observations may be significantly unreliable given that men were asked to report this information 20 to 50 years later.

More interestingly, over a lifetime, the authors found the opposite result: a decreased risk of prostate cancer for people with low ejaculatory frequency.

Corroborating with the other 3 studies quoted at the top of this article, we conclude that the risk of prostate cancer actually decreases with more abstinence. It is unfortunate that a large part of the media promotes the exact opposite of this fact.