Women with demanding jobs were more likely to develop breast cancer in a 14-year Swedish study.

The work with 36,000 Swedish women started in 1990 with volunteers taking a survey.

By 2004, 767 of the women -- about 2 percent -- had been diagnosed with breast cancer.

Researchers said they found that full-time working women in stressful jobs were 30 percent more likely to develop breast cancer, but that there was no link between stress and breast cancer in part-time workers.

They said in a news release that stress may be linked to an increase in estrogen, which increases the risk of cancer.