But women who have been through the menopause may actually be protected by smoking - that is, it might reduce their risk for breast cancer. The researchers think that it's because smoking has an antiestrogenic effect - in other words, it reduces your oestrogen levels.
"Smoking before menopause was positively associated with breast cancer risk, and there were hints from our results that smoking after menopause might be associated with a slightly decreased breast cancer risk," say the study's authors.
However passive smoking, light and moderate smoking was not linked to breast cancer. "Although an elevated risk for light smokers and moderate smokers was not apparent, heavy smokers who started smoking early in life, smoked for a long duration and smoked a high quantity were at the highest risk of breast cancer," the researchers add.
Is the jury still out on smoking and breast cancer? What do you think?