The large study reviewed here offers a reassuring message for coffee drinkers: caffeine, even in large amounts, doesn't increase breast cancer risk. These results add to other research that also has found no link between caffeine and breast cancer risk.
The researchers looked at the health information of more than 39,000 women who participated in the Women's Health Study. None of the women had been diagnosed with breast cancer when the study started. Questionnaires asked the women about their diets, including how much caffeine they consumed each day. Most of the caffeine came from coffee, but tea, diet and regular cola, and chocolate also added to daily caffeine consumption:
The researchers compared the caffeine intake of women who developed breast cancer to the caffeine intake of women who didn't develop breast cancer. The analysis found no link between overall breast cancer risk and caffeine intake. The way the caffeine was consumed (in coffee, tea, cola, or chocolate) also didn't have any effect on risk.
The results did show a slight increase in the risk of hormone-receptor-negative breast cancer among women who consumed the largest daily amounts of caffeine, but the researchers said this increase was likely due to chance and not due to caffeine consumption.
The researchers also found slight increases in risk among women with a history of non-cancerous breast disease who consumed large amounts of caffeine daily. Still, this increase also was likely due to chance and not due to caffeine consumption.
While there seems to be no link between caffeine and breast cancer risk, other diet and lifestyle choices can affect your risk of breast cancer. Visit the Breastcancer.org Lower Your Risk section to learn about diet and lifestyle options to keep your risk as low as it can be.
BOSTON, Oct. 13 (MedPage Today) -- Several cups of coffee a day do not seem to pose an overall breast cancer risk, researchers here found in a large cohort study, confirming other research.
Breast cancer risk was not significantly elevated overall by drinking four or more cups of coffee a day (relative risk 1.08, 95% confidence interval 0.89 to 1.30), reported Shumin M. Zhang, M.D., of Brigham and Women's Hospital and Harvard, and colleagues in the Oct. 13 issue of the Archives of Internal Medicine.
Nor did women with even the highest level of caffeine consumption appear to be at elevated risk (RR 1.02, 95% CI 0.84 to 1.22) in the analysis of the prospective Women's Health Study.
But as in some previous studies, high caffeine consumption appeared to increase risk for women with a history of benign breast disease. Risk was also elevated for developing hormone receptor-negative or larger tumors.
The researchers cautioned though, that these subgroup findings may be due to chance.
The overall lack of association between caffeine and caffeinated drinks was generally consistent with results from prior prospective cohort studies in Western countries, such as the Nurses' Health Study, they noted.
Dr. Zhang's group analyzed caffeine intake from food frequency questionnaires completed by 39,310 female health professionals participating in the Women's Health Study.
The primary prevention trial randomized women ages 45 and older without cancer or cardiovascular disease to low-dose aspirin and vitamin E.
Participants primarily drank coffee (81.3%), although tea (10%), diet cola (5.6%), regular cola (1.2%), and chocolate (0.3%) also contributed to their daily caffeine consumption.
Most women reported either never drinking coffee (24.1%) or two to three cups a day (32.8%). About 15% were in the highest intake category with at least four cups a day.
Overall caffeine intake was not linked to breast cancer risk for the women nor was any individual caffeinated beverage or food. The relative risks in the multivariate analysis controlling for age, randomized prevention treatment, and breast cancer risk factors were:
However, for women with a history of benign breast disease, there was a borderline significant elevation in breast cancer risk with the highest caffeine intake (RR 1.32, 95% CI 0.99 to 1.76) and with at least four cups of coffee per day (RR 1.35, 95% CI 1.01 to 1.80).
Caffeine was also associated with increased risk in women with poor breast cancer prognosis. The highest intake levels were associated with significant risk of estrogen- and progesterone-receptor breast cancer (RR 1.68, 95% CI 1.01 to 2.81, P=0.02 for trend) and tumors larger than 2 cm (RR 1.79, 95% CI 1.18 to 2.72, P=0.02 for trend).
Other breast cancer characteristics, body mass index, menopausal status, and hormone therapy use did not appear to impact the associations overall.
Although these findings would suggest caffeine affects breast cancer progression independent of the estrogen pathway, the researchers noted that the results were not in line with those of the Iowa Women's Health Study and the Nurses' Health Study, which also looked at caffeine's impact by hormone receptor status.
Dr. Zhang and colleagues cautioned that they could not exclude the possibility that these were chance findings because of the large number of subgroups evaluated. Further study is warranted, they said.
Another limitation of the study was data on caffeine intake only at baseline, which did not account for changes over time and would have tended to weaken any true associations, they noted.
The study was supported by research grants from the National Institutes of Health. The researchers reported no conflicts of interest.
Primary source: Archives of Internal Medicine Source reference: Ishitani K, et al "Caffeine Consumption and the Risk of Breast Cancer in a Large Prospective Cohort of Women" Arch Intern Med 2008; 168: 2022-2031.
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