避孕药易引起前列腺癌

Use of the contraceptive pill（避孕药） is associated with an increased risk of prostate cancer around the globe, finds research published in BMJ Open. Prostate cancer is the most common male cancer in the developed world and the use of the contraceptive pill has soared over the past 40 years, say the authors.

The research team used data from the International Agency for Research on Cancer (IARC) and the United Nations World Contraceptive Use report to pinpoint¹ rates of prostate cancer and associated deaths and the proportion of women using common methods of contraception for 2007.

They then analysed the data for individual nations and continents worldwide to see if there was any link between use of the contraceptive pill and illness and death caused by prostate cancer.

Their calculations showed that use of intrauterine（子宫内的） devices, condoms, or other vaginal（阴道的） barriers was not associated with an increased risk of prostate cancer.

But use of the contraceptive pill in the population as a whole was significantly associated with both the number of new cases of, and deaths from, prostate cancer in individual countries around the world, the analysis showed. These findings were not affected² by a nation's wealth.

The authors emphasise³ that their research is speculative⁴（投机的，推测的） and designed to prompt further consideration of the issues. As such, their analysis does not confirm cause and effect, and therefore definitive⁵ conclusions cannot be drawn⁶, as yet.

But they refer to several recent studies which have suggested that oestrogen（雌激素） exposure may boost the risk of prostate cancer.

Excess oestrogen exposure is known to cause cancer, and it is thought that widespread use of the Pill might raise environmental levels of endocrine（内分泌） disruptive compounds (EDCs) -- which include by-products of oral contraceptive metabolism⁷.

These don't break down easily, so can be passed into the urine and end up in the drinking water supply or the food chain, exposing the general population, say the authors.

"Temporal increases in the incidence of certain cancers (breast, endometrial, thyroid, testis and prostate) in hormonally sensitive tissues in many parts of the industrialised world are often cited as evidence that widespread exposure of the general population to EDCs has had adverse⁸ impacts on human health," they write.