Summary

A prospective large-scale study is reported which investigates the relationship between caffeine consumption and the risk of breast cancer. This shows that while there is no overall increased risk, there are sub-categories where such an increased risk seems to exist, namely existence of benign breast disease and also hormone-negative breast cancers, and tumors greater than 2 centimeters in diameter.

Introduction

Caffeine, in the form of tea, coffee, chocolate and cola, is one of the most widely consumed, biologically active substances in the world. Accordingly, there have been concerns that long-time consumption might lead to health problems. It has previously been reported that caffeine might raise the risk of breast cancer. This is because women with non-cancerous (benign) breast disease improved when they cut caffeine out. Benign breast disease is, in itself, a risk factor for breast cancer. Therefore there is an indirect link between caffeine consumption and breast cancer.

What was done

Researchers at Brigham and Women's Hospital and Harvard Medical School, and at Tokyo Women's Medical University,. carried out a prospective study of 38,432 women aged 45 or more who provided them with dietary information on caffeine consumption from 1992-1995. The women were followed up for an average of 10 years and cases of breast cancer recorded.

What was found

During the follow-up time, there were 1,188 women with invasive breast cancer. Overall, there was no increased risk of breast cancer with increasing caffeine consumption. However, drilling down into the data revealed some interesting associations. Among women with benign breast disease, there was a significant association between breast cancer and the highest levels of coffee consumption (four or more cups a day).

There was also a 68 percent increase risk of estrogen receptor-negative and progesterone receptor-negative breast cancers and caffeine consumption. These are the breast tumors to which hormones do not bind and they are treated differently from the hormone-positive breast cancers. There was also a 79 percent increased risk of developing a breast tumor larger than two centimeters in diameter with increasing caffeine consumption.

What this study means

It may be that, for women with benign breast disease, caffeine can accelerate the progression to breast cancer which is possible with this condition. The fact that caffeine increases hormone-negative, but not hormone-positive, cancer, suggests it may act independent of the (already well known) estrogen pathway. Caffeine is a molecule with many biological effects - on the cell cycle, cell death and elsewhere. These need further investigation to see whether they can promote breast cancer.