Popular legal stimulants coffee and tea do not increase a woman's risk of developing breast cancer.
This good news comes from the Nurses' Study — a massive prospective study in which researchers from the Harvard School of Public Health followed more than 85,000 women for 22 years.
"In this large cohort of women, with 22 years of follow-up, we observed no association between coffee (caffeinated or decaffeinated) and tea consumption and the risk of breast cancer," Harvard's Dr. Davaasambuu Ganmaa told Reuters Health.
"Coffee and tea are remarkably safe beverages when used in moderation."
Ganmaa and colleagues assessed coffee, tea, and caffeine consumption among 85,987 women who participated in the Nurses' Health Study. The women were between 30 and 55 years old at the start of the study.
22 years later, 5,272 women had developed breast cancer.
After accounting for other factors associated with breast cancer risk, such as age, smoking status, body mass, physical activity, alcohol intake, family history, menopausal status, history of hormone therapy, and number of children, the researchers found no increased risk of breast cancer for women who drank 4 or more cups of caffeinated or decaffeinated coffee or tea per day, compared with those who drank less than 1 cup daily.
They also found no apparent association between the occurrence of breast cancer and intake of other caffeinated soft drinks and chocolate.
In fact, when the researchers measured breast cancer risk among postmenopausal women, they discovered that high caffeine intake actually lowered cancer risk slightly. But, "this relation needs to be examined further," the investigators note.
The study appears in the May 2008 issue of the International Journal of Cancer.