A common misconception is growing that a link exists between caffeine and the development of breast cancer. While caffeine is known to increase the discomfort associated with fibrocystic breast disease--a condition where small lumps can form in the breast tissue--the likelihood that its ingestion increases the risk of overall breast cancer is low.
Caffeine
A study led by the Obstetrics & Gynecology Epidemiology Center at the Harvard Medical School in 2002 found that caffeine consumption was not associated with breast cancer incidence. Women drinking four or more cups of coffee per day had a 0.94 relative risk of developing breast cancer compared to those drinking only one cup a day. Statistically speaking, there isn't much of a difference between the two groups. The risk was slightly greater for women drinking tea, coming in at 1.13 relative risk. For overall caffeine consumption, women in the highest quintile had a 1.04 risk than those in the lowest. For comparison, a risk ratio of 1 basically means the chances of developing breast cancer are equal in both groups, so 1.04 means the risk is just slightly greater, but not significantly.
Further Evidence
A study conducted in 2008 in conjunction with the Department of Epidemiology at the Harvard Medical School supports the previous findings. Over 38,000 cancer-free women were detailed at the start of the study and then again after 10 years. Of these women, 1,188 were identified with invasive breast cancer. No association was made between caffeine consumption and breast cancer risk, with numbers similar to the 2002 study. Those in the highest quintile for caffeine consumption had a 1.02 relative risk of developing breast cancer. Those getting caffeine from coffee had a 1.08 relative risk, while those drinking tea had a 1.03 relative risk.
Breast Disease
Caffeine consumption may, on the other hand, increase the risk of breast cancer in women with benign breast disease. The study conducted in 2008 found that women in the highest quintile of caffeine consumption--which was set at four or more cups of caffeinated beverages a day--had a marginally significant risk of developing this disease. These women were also more likely to develop either estrogen receptor-negative or progesterone receptor-negative breast cancers as well as tumors larger than 2cm. Further studies are necessary to determine the exact link.
Recommendation
Although a link between caffeine and breast cancer is unlikely, the Mayo Clinic recommends getting no more than 200 to 300mg a day. This suggestion isn't based on the risk of breast cancer. Instead, it stems from the potential side effects of this stimulant, which includes nervousness, restlessness, irritability, muscle tremors, upset stomach and insomnia. It's also known to increase your heart rate.
References
- MedlinePlus; Fibrocystic breast disease; January 2011
- "Annals of Epidemiology"; Coffee, Tea and Caffeine Consumption and Breast Cancer Incidence in a Cohort of Swedish Women; K.B. Michels, et al.; January 2002
- "Archives of Internal Medicine"; Caffeine Consumption and the Risk of Breast Cancer in a Large Prospective Cohort of Women; Ken Ishitani, et al.; October 2008
- National Cancer Institute; Breast Cancer; October 2009
- MayoClinic.com; Caffeine: How much is too much?; March 2011
