Smoking before menopause linked to breast cancer

Women who smoke heavily before the menopause, especially prior to giving birth, may significantly increase their risk of developing breast cancer, research suggests.

A US study of almost 150,000 women found that breast cancer rates increased with higher levels of smoking among younger age groups.

“Smoking before menopause was positively associated with breast cancer risk,” the authors wrote in the journal Archives of Internal Medicine.

The size of the effect was “modest”, said the scientists led by Dr Fei Xue, from Harvard Medical School, Boston.

They added that smoking after the menopause slightly reduced the risk of breast cancer, possibly because it helped lower levels of the hormone oestrogen.

Although smoking is a well-known risk factor for other cancers, its relationship with breast cancer is controversial.

Previous studies have shown mixed results and some even suggest that smoking might protect against the disease.

The new research is based on data from the Nurses’ Health Study, a major US investigation of the factors that affect women’s health.

No significant association was seen between passive smoking, or light and moderate smoking, and breast cancer. But women who smoked heavily and took up the habit early in life were at increased risk.

For those who started using tobacco before giving birth for the first time, smoking the equivalent of 20 cigarettes a day for 20 years raised the risk of breast cancer by 18%.