Young women who smoke are more prone to breast cancer than those who smoke later in life or never smoke, says a study.

Janet Olson and other researchers in the Mayo Clinic at Rochester found that women who smoke cigarettes before their first pregnancy have a 20 percent more risk of getting breast cancer, reports science portal EurekAlert.

In comparison, women who started smoking after the birth of the first child or were never smoked enjoy relative immunity.

The researchers used data from a study that covered 41,836 women from Iowa, aged 55 to 69 years.

The study was designed to identify risk factors for cancer and other chronic diseases in postmenopausal women.