Sunday, April 27, 2008

And It Won't Make You Blind, Either

Photo of a geyser in Iceland by Flickr user Benzpics63, used under a Creative Commons license.

Ben Harder, science journalist at U.S. News and World Report, is calling out the major news services for recycling a five-year-old study on prostate cancer as if it were fresh news. He's right to criticize their sloppy reporting, of course. He was wrong, however, to suggest that the study is dubious just because it's not brand-new. Given the study's content, I hope that the screw-up in reporting will give it more exposure than it might otherwise get. When I read about it a few months ago, my reaction was: Wow, this is news that helps men take their health into their own hands, if you'll forgive a bad pun. So why isn't it already common knowledge?

What a group of Australian scientists found is this: Masturbation may offer protection against prostate cancer. And actually, not just masturbation but any sexual activity resulting in ejaculation. The group, headed by Dr. Graham Giles, found that men in their twenties who ejaculated at least seven times per week reduced their risk of prostate cancer by one-third compared to those who ejaculated fewer than three times per week. That's a remarkable figure.

The explanation Dr. Giles offered when the study was published in 2003 makes intuitive sense to me, even if it's still somewhat speculative. Basically, to use a rather unfortunate plumbing metaphor, he suggested that the pipes stay cleaner and healthier when flushed out regularly:
Our research indicates that there is no association between prostate cancer and the number of sexual partners, which argues against infection as a cause of prostate cancer in the Australian population.

We also found no association between maximum number of ejaculations in a 24 hour period and prostate cancer. Therefore, it is not men's ability to ejaculate that seems to be important.

While it is generally accepted that prostate cancer is a hormone dependent cancer, apart from age and family history, its causes are poorly understood.

For this reason, our explanations are fairly speculative - one possible reason for the protective effects of ejaculation may be that frequent ejaculation prevents carcinogens building up in the prostatic ducts.

If the ducts are flushed out, there may be less build up and damage to the cells that line them.
Ben Harder did find one subsequent study, published in 2004, that strikingly corroborated the Australians' findings. That study found:
Each increment of 3 ejaculations per week across a lifetime was associated with a 19% (95% CI, 7%-30%) decrease in risk of organ-confined prostate cancer.
Its lead author, Dr. Michael Leitzmann, told Harder he's certain no further work has been done on this topic. Why???

These studies found a free, simple, and fun way a man can protect himself against a cancer that strikes one in five men. Yet I'll bet more adult men are aware of other habits that protect against prostate cancer, such as drinking tea and eating tomatoes. As a gal who calls herself Sungold, I'm unabashedly pro-tomato; but why should tomatoes get all the press while the benefits of ejaculation are ignored?

I can only think our deep cultural ambivalence about sex is to blame. That would explain why this news failed to make a splash five years ago. And that also accounts for the dearth of follow-up studies, which mirrors the shameful underfunding of research on prostate cancer in general. This anti-sex mindset is also deeply anti-scientific, preoccupied with ideas about purity that date all the way back to Leviticus.

Artwork by Flickr user adamrice, used under a Creative Commons license.

(In case you can't read the quotation from Leviticus 15:16-17 in the image above: "And if any man's seed of copulation go out from him, then he shall wash all his flesh in water, and be unclean until the even. And every garment, and every skin, whereon is the seed of copulation, shall be washed with water, and be unclean until the even.")

If it seems like I'm making too much of this, check out this comment, copied verbatim from Harder's blog:
how can anyone condone masterbation? in the Bible it is widely and worldly known as a sin! you will be sending people straight to hell.
Unfortunately, it's also "widely and worldly known" that this is the brand of thinking that brought anti-condom AIDS education to Africa, sees cervical cancer as the just wages of sin, and believes comprehensive sex education causes teenage pregnancy. In this worldview, a few million excess cases of prostate cancer might seem like a cheap sacrifice in creating a moral dystopia where the only pleasure is feeling holier-than-thou.


figleaf said...

I think there are two things to keep in mind about Harder's post.

First, I don't remember there being much buzz about the Australian study five years ago. Or the four-year-old NIH study that corroborated the first. If there was a giant fuss the first time, and this is all just round two of the same info then fine, Harder's got a point. (Although an ironic one considering the journalist's lament about "today's best reporting is tomorrow's fish wrap.)

The other point is that if two independent studies a year apart that use even slightly different methodologies come up with virtually identical results then... why the heck would anyone waste good grant money following up with a third? (That's not to say more credible research into *other* health benefits and/or risks of frequent vs. infrequent ejaculation wouldn't be useful. But it sounds like the prostate correlation is in the bag.)

Sungold said...

Harder has a point in any event that it's silly to present this *as if it's new.* But it's good to know that you don't remember hearing about this, either, because it probably means it really didn't make news at the time.

The fish wrap metaphor is not going to make any sense to our grandchildren, who will wonder how the heck you're supposed to wrap a computer around anything!

You have a good point about the grant money. The studies' methodologies *were* different. The one in Oz relied entirely on questionnaire data reported after the fact, while the NIH one was partly prospective since it followed a group of men all through the 1990s (but did use retrospective data to get at earlier behavior). Both looked at relatively large populations (at least 1000 healthy and 1000 diagnosed men in each study).

If you look at how the studies' results were reported in the medical journals, you can see that they weren't actually designed to find a benefit of ejaculation - this was an incidental finding! They were trying to examine the presumed *negative* impact of sexual activity on prostate health, which a prior meta-analysis had found. Both studies state that they found no evidence that greater sexual frequency raised the risk of PCa.

So part of what's going on here is a paradigm shift. My guess is that it would be useful to extend the NIH data with another round of questionnaires in 2010 (the original study looked at 1992-2000) and see if the original findings still hold up. But it doesn't look as though there are plans to do that. To me, the NIH results, in particular, look pretty convincing but the authors stated them in pretty cautious tones and also noted that they don't really understand the mechanisms through which frequent ejaculation may be protective.

At any rate, I think it's safe to say the benefits vastly, vastly outweigh the risks. Thanks, figleaf!