A premature menopause, usually due to removal of the ovaries, nearly doubles the risk of lung cancer in women, a new study shows.

There was also evidence that an early natural menopause may increase the risk of lung cancer.

In the study, a premature menopause was identified as a risk factor for lung cancer and this was an unexpected finding, study chief Dr. Anita Koushik, from the University of Montreal, told Reuters Health.

The "case-control" study was conducted in Montreal and featured 422 women with lung cancer (the cases) and 577 without the malignancy (the controls).

Koushik and colleagues report that most menstruation and pregnancy factors had little or no effect on the risk of lung cancer. "Non-natural" menopause, induced by removal of the ovaries, however, increased the odds of lung cancer by nearly twofold.

The results also indicate that women who were younger at menopause were at greater risk for lung cancer than those who were older when they entered menopause.

The findings held true for all levels of smoking, the researchers report in the latest issue of the International Journal of Cancer.

Regarding future research, Koushik commented that "we need to know if this association is real, and if so, how can we explain the association. New studies can address whether the association is related to an early age at menopause, or due to hormone replacement therapy use, or something else."