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The link between prostate cancer and sexual activity. 

In ‘My doc says men need sex 27 times a month, but who gets that?’, the famous Canadian rocker—known for lyrics such as “I want to be your underwear”—alludes to the link between a man’s sexual health and prostate cancer. 

In 1853, J. Adams, a surgeon at The London Hospital, described the first case of prostate cancer which he called a “very rare disease.” Today, prostate cancer is the second most common cancer in men, behind skin cancer—my specialty. But as happens with statistics about big health questions, there are many back stories that beg for more interrogation. The prostate cancer conundrum ends up a fascinating study of human culture. For example, why is it that increased incidence of prostate cancer is related to the ‘Western’ lifestyle? While the incidence of clinical prostate cancer is significantly lower in Asian populations, the risk increases if an Asian man migrates to Western countries. Is it to do with diet? Lifestyle? Or not enough sexual activity? (Is Bryan Adams’s doctor, right?)

Forty years after Adams had described the first case of prostate cancer, a Philadelphia surgeon W. White measured changes in the size of the prostate gland in dogs after they were neutered and found that the gland shrank in size. This link between prostate cancer and testosterone levels is why anti-androgen hormone treatment is used for prostate cancer. 

The Harvard ejaculation study collected information from nearly 30 thousand men over two decades. These were all male health professionals: doctors, dentists, pharmacists, veterinarians, optometrists, ophthalmologists, and podiatrists aged between 46 and 81. Information about their average number of ejaculations per month in young adulthood (age 20–29), middle age (40–49), and in the most recent year was recorded until 2000. The results were surprising. Even after accounting for lifestyle measures, high ejaculation frequency was linked to a decreased risk. Men who ejaculated 21 or more times a month had a 31% lower risk of prostate cancer compared to men who reported 4–7 ejaculations per month across their lifetimes. I must clarify that the ejaculation study included all forms of ejaculation—sexual intercourse, nocturnal emissions, and masturbation—to avoid outrage from, or pressure on, unwitting or unwilling female victims of this prostatic predicament.

Another study from Australia looked at ejaculatory frequency and prostate cancer risk. Again, this study evaluated total ejaculations including wet dreams and masturbation rather than focusing only on carnal relations. The results were surprisingly similar to the American study: men who averaged 4.6–7 ejaculations a week were 36% less likely to be diagnosed with prostate cancer when compared to males who ejaculated less than 2.3 times a week.

Another interesting commonality in these studies was the finding that ejaculatory frequency before age 40 had the greatest effect. It is similar to the effect we see in skin cancer causation—childhood and younger age sunburns increase your risk of skin cancer later on. But in the case of skin cancer, we know it is because ultraviolet (UV) rays induce genetic mutations in skin cells. But we do not still know why an increased number of ejaculations in men under 40 reduces the risk of prostate cancer later on. 

 

One of the problems with prostate cancer is predicting which ones will become aggressive. Most men actually die with prostate cancer, rather than, because of. But recent advances in prostate science suggest that the microbiome matters.

Microbiomes represent microbes – bacteria, fungi, viruses, and of course their genomes that live inside or on our bodies. As a skin doctor, I have been interested in the skin microbiome. Gut microbiomes have perhaps been more studied than any other. A study from the University of East Anglia conducted genetic assays on urine and prostate samples on more than 500 men and found that certain bacterial species were linked to aggressively progressive prostatic cancer. If one could identify rapidly progressive prostatic cancer by simply looking for these bacteria, one could treat the disease early. Or if these bacteria were the cause of prostate cancer, new antibiotics could be a game changing cure.  The Guardian quoted Dr Hayley Luxton of Prostate Cancer UK, which partially funded the research as saying, “This is an exciting discovery that has the potential to truly revolutionise treatment for men.” This study, published in European Urology Oncology found that four bacterial species –Porphyromonas, Varibaculum, Peptoniphilus, and Fenollaria—were repeatedly found in the urine of men with progressive prostate cancer. Do I hear you say that you have never heard of these bacterial species before? Neither had I. These are novel, previously unidentified bacteria that we now know are frequently found in the urine of patients with aggressive prostate cancer. Researchers are still uncertain if these bacteria are specifically involved in the disease causation, or if men with aggressive prostate cancer have deficient immune systems that allow these bacteria to thrive. Either way, the study implicated these specific organisms. Is this why Western diets increase risk, but spicier Asian diets do not appear to? We don’t know the answer yet. However, killing these creatures won’t be easy. Dense tissue such as the prostate gland is not easy for antibiotics to penetrate, and given these are new microbial species, possibly new antibiotics will need to be developed. 

In research speak, a meta-analysis is like the Book of Genesis. A heavy-duty effort. Being a collated analysis of combined results from many studies, standard scientific opinion is that a meta-analysis always ranks higher than a single study and is one of the best forms of research. But the nature of meta-analyses—the scope and loftiness of purpose obscures a fundamental problem—is that they are subjective and non-experimental. Judgments are made every step of the way, allowing academics—usually like-minded people with similar personalities—to be steered down precipitous paths that can sometimes unbalance them. But in science, as in the race of life, the inside lane and the outside lane sometimes differ only in intention not actuality. A study into the ultimate form of study i.e., research into meta-analyses concluded that 80% of the time the conclusion of a meta-analysis was pretty much the same as that of a single major study. In other words, understanding this dominant study within a meta-analysis is crucial. 

A recent meta-analysis of the previous studies that looked at ejaculatory frequency and prostate cancer found that the actual differences were indeed small. However, this study indicated that men with fewer sexual partner numbers, older age at first intercourse, and moderate frequent ejaculation were associated with a significantly decreased risk of prostate cancer. The risk of prostate cancer was decreased by 4% for every 5-year delay in the age at which the man had had sex for the first time. The reduction in risk when a man had fewer partners may be related to the novel bacterial species we discussed earlier. Fewer partners mean less comingling and reduced opportunity for bacterial transmission to occur. The meta-analysis did not show a linear association between prostate cancer and ejaculatory frequency but suggested that ejaculating two to four times a week does reduce a man’s risk of prostate cancer. 

What this ultimately means is—while researchers were honest about everything, they were not certain about everything—and the jury is still out.

THE END