It may not fall into the "shocking" category, but a new Harvard study by our colleagues at the Nurses' Health Study has provided further insight into the links between smoking and breast cancer (study). To date, many studies have had waffling results on the subject. Some showing smoking raising risk; some showing it not affecting risk at all; and some even showing it lowering risk.
This new study by Xue et al is a longer followup to an earlier Nurses' Health Study report and included over 110,000 women who were tracked over a 30 year period. The main finding from this study was that smoking likely has some affect on breast cancer risk, but even with heavy smoking, the risk isn't as high as with other cancers linked to smoking (like lung, oral, and esophageal cancer, to name just a few). Greatest risk came from heavy smoking before giving birth to a first child, which raised risk by about 18 percent compared to never smoking. The broad analysis comparing those who have ever smoked to those who have never smoked showed a small six percent increase in risk.
Not surprisingly, heavy smoking after menopause showed a small protective effect against breast cancer. After menopause, blood estrogen levels drive a lot of breast cancer risk, and for multiple reasons, smoking stems estrogen levels, which in turn could lower risk after menopause. Increases in risk, though, from smoking before menopause outpaced any small drop in risk from smoking afterward.
So what do these results mean? While there are still some open questions about the link between smoking and breast cancer, they certainly add one more reason to avoid smoking and to support policies that lead to that end. Adding breast cancer to the list, there are no fewer than 12 different cancers caused by or directly linked to cigarette smoking. Heart disease, diabetes, stroke, chronic bronchitis, emphysema, osteoporosis, and a number of other important conditions belong on the list as well. With the decline in US smoking rates stalling - leaving just over 20 percent of the population regular smokers (previous post) - it's important that we keep our guard up against tobacco use. It's been a long fight, and we've gained a lot of ground, so it's easy to feel that we've done what we can and move on to some new health promotion venue. But, really, smoking still deserves a great deal of attention. The potential health gains from further lowering smoking rates are huge and should not be downplayed just because we've made some strides and have been working on the issue a long time.