Could birth control pills be linked to an increased incidence of prostate cancer around the world? That's the provocative question being raised in new research published this week in BMJ Open.
Dr. Neil Fleshner, a urologic oncologist and researcher at Princess Margaret Hospital in Toronto, says he and his co-author had long wondered why men in North America and Europe develop and die of prostate cancer more often than men in other countries.
"For years, there's been concern that perhaps maybe pesticide exposure or some kind of compound in our food or water supply may be responsible for prostate cancer," he says.
So he and his team reviewed data from the United Nations World Contraceptive Use report, looking at contraceptive use among women around the world.
They found that the use of IUDs (intrauterine devices), condoms, and other vaginal barriers were not linked to an increased risk of prostate cancer, but the use of the birth control pills was significantly associated with both a country's number of new cases of prostate cancer and deaths from prostate cancer.
When countries like Canada and the U.S., which both have a high proportion of women using oral contraceptives, are compared to countries like Japan, which has a low usage, there's close to an eight-fold difference in prostate cancer death rates.
"There appears to be a link between oral contraceptive use in populations and the development of prostate cancer in those populations," Fleshner said.
The authors emphasize that their research is very preliminary and they are not trying to draw conclusions about cause and effect. Still, they say their finding should prompt further consideration of the idea that birth control pills are fuelling prostate cancers.
As for how women's contraceptive use could be affecting men, Fleshner says it's possible that synthetic estrogen is being excreted into the women's urine, which is then contaminating our water supply.
"The prostate is a reproductive organ and we know that it's sensitive to reproductive hormones such as estrogens and testosterone, and hence the link," he says.
"It's possible and plausible that somehow, that is working its way back into our food chain or water chain, and therefore perhaps being responsible for this."
Other research has shown that trace amounts of dozens of pharmaceuticals -- including antidepressants and antibiotics -- are ending up in our wastewater. Most existing filtration systems can't remove these chemicals and some of them can disrupt hormones.
Dr. Laurence Klotz, the chief of Urology at Sunnybrook Health Sciences Centre in Toronto, says the study is an interesting one but there are still many questions left to answer.
"It's a very preliminary study, it only shows an association and an association does not mean a causation," he says.
"It's the first time this has been examined this way, and it's a comprehensive look at it. But the difficulty with these large association studies is they don't show a cause."
Klotz says there are likely many causes of prostate cancer that include environmental causes, lifestyle causes and genetics.
"We know a lot about prostate cancer. It's partly genetic, it's partly related to diet, to intake of micronutrients. In Japan, there was a low incidence of prostate cancer and when they adopted a more Western diet, their rate of prostate cancer shot up," he says.
Fleshner says his study should not prompt women to throw away their oral contraceptive pills.
"The major take-home message from our study is that we need to investigate the link between these two conditions, between the use of oral contraception and prostate cancer. There's no need for panic," he said.
With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip
