Kick Breast Cancer Do it for your girls: Women who have infrequent or no vaginal intercourse are three times more likely to develop breast cancer than those who have more, according to a French study in the Journal of Clinical Epidemiology. In addition, an earlier American study found that women whose partners used condoms or withdrawal, as well as women not engaging in intercourse at all, had a breast cancer rate five times higher than users of contraceptives that do not reduce vaginal exposure to semen. There are a couple of theories why. Some researchers believe sperm contains antigens that are absorbed through the vagina. Other says oxytocin and DHEA-two "happiness hormones" that increase with arousal-may have a protective effect. READ 12 REASONS TO HAVE SEX