Caffeine & breast cancer risk

The relationship between caffeine consumption and breast cancer has been a point of contention for a while. While most studies have not shown an association, several have shown an inverse relation or a weak positive association. Two recent studies from the United States have further examined this relationship.

The first study from the Brigham and Women’s Hospital took detailed dietary information from 38,432 women who were 45 years or older and were free from cancer during the period 1992 – 1995 (Arch Intern Med 2008; 168: 2022 – 2031). These women were followed up for a mean period of 10 years. Women who almost never drank coffee and those who drank 4 or more cups of coffee daily did not show an increased risk of developing breast cancer. The same findings were seen in women who drank tea (≥ 2 cups daily vs almost never). However, the study did find a borderline significant positive association with breast cancer risk in women with existing benign breast disease who consumed the most amount of caffeine and coffee. The study also found a significant association between caffeine consumption and the risk of developing estrogen and progesterone receptor-negative breast cancer (68% more likely) and breast tumours larger than 2 cm (79% more likely).

In another report from the Harvard School of Public Health, 85,987 female participants in the Nurses’ Health Study were followed up for 22 years (Int J Cancer 2008; 122: 2071 – 2076). Their consumption of coffee, tea and caffeine consumption was assessed in 1980, 1984, 1986, 1990, 1994, 1998 and 2002. Women who consumed ≥ 4 cups of coffee / day did not have an increased risk of developing breast cancer. Similarly, intake of tea and decaffeinated coffee was not associated with breast cancer risk. However, in postmenopausal women, an inverse association was found. There was a 12% difference in the risk of breast cancer for the highest intake group compared to the lowest intake group.

While these two big studies have shown that caffeine in general is not associated with risk of breast cancers, too much caffeine can be bad for a sub-set of women. If you were to develop breast cancer, caffeine consumption may give rise to poorer tumour characteristics. While this is not confirmed beyond reasonable doubt, it might be prudent for you to remember the saying ‘Everything in moderation please’ while the jury is still out.