Consuming grapefruit appears to increase risk of breast cancer in post-menopausal women, according to a study in British Journal of Cancer (July, 2007) (Prospective study of grapefruit intake and risk of breast cancer in postmenopausal women: the Multiethnic Cohort Study)

One quarter grapefruit per day compared to none increased risk by about one third. The significance of this slightly increased risk is underscored by 2 factors — women are taught lifelong to associate grapefruit intake with health and with weight-control (the “Grapefruit diet”).

The factor involved in the increased risk is a chemical in grapefruit (CYP3A4) that blocks the body’s breakdown of estrogen.

Since vitamin C and other antioxidants found in grapefruit are readily available from other fruits, with this new information women can choose to switch to oranges, tangerines, lemon juice, and other fruits and avoid grapefruit.