A new study has found that women who smoked before menopause were found to have a higher risk of breast cancer than non-smokers.
Using data collected from the Nurses' Health Study, Fei Xue, of Brigham and Woman's Hospital and Harvard Medical School, Boston, and colleagues examined the records of 111,140 women from 1976 to 2006 for active smoking and 36,017 women from 1982 to 2006 for passive (secondhand) smoking.
A total of 8,772 breast cancer cases developed during follow-up. The development of breast cancer was associated with a higher quantity of current and past smoking, smoking for a longer period of time, younger age at smoking initiation and more pack-years (product of the number of packs per day and the number of years that quantity was smoked) of smoking.
"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," the authors write.
"This difference suggests an antiestrogenic effect of smoking among postmenopausal women that may further reduce their already low endogenous estrogen levels."
The study has been published in Archives of Internal Medicine.