Coffee isn’t harmful to your health, a new study confirms that theory. Is it true that long term, regular coffee consumption may speed the progression of aggressive forms of breast cancer? The findings of a new study published in the Oct. Issue of the Archives of Internal Medicine suggest caffeine “does not appear to be associated with overall risk of breast cancer.”

For the study, funded by the National Institutes of Health, study co-author Dr. Shumin M. Zhang, from the division of preventive medicine, in the department of medicine at Brigham and Women's Hospital and Harvard Medical School in Boston and colleagues from Tokyo Women’s Medical University in Japan examined the diets of a pool of almost 39,000 women over the age of 45 over a period of ten years. The participants were asked to provide details of their diet, including their coffee habits. 1,188 of the 38,432 study participants developed invasive breast cancer over 10 years of follow-up.

The researchers concluded that consumption of caffeine – found in coffee, chocolate, tea, soft drinks and other caffeinated beverages – was not “significantly” associated with an overall increased risk of breast cancer.

Among women with a history of benign breast cancer disease, those consuming four or more cups of coffee a day have a “borderline significantly increased risk” for malignant disease. A high-caffeine diet also increased the likelihood of growing tumours larger than two centimetres. The findings also suggest that caffeine consumption may speed the progression of existing tumours. Caffeine raised the risk for tumours larger than two centimetres by 79 percent, the researchers found.

The risk of developing certain forms of breast cancer and for tumours that are negative for both estrogen receptor (ER) and progesterone receptor (PR) also rose for heavy caffeine consumers. Zhang and his team say that more research is needed to determine if the finding is real.

However, the results of this large study should be reassuring to the majority of women, who like to drink coffee moderately, as researchers conclude that moderate caffeine consumption does not increase breast cancer risk. We may say that coffee isn’t the “magic drink” but isn’t going to hurt you either.

Previous studies have shown that caffeine has some beneficial health effects, such as a lower risk of dying from heart disease; caffeine consumption could also protect us against multiple sclerosis as it blocks the key steps in the development of the disease. Women consuming two to three cups of coffee per day had a 25 per cent lower risk of death from heart disease, compared with those who did not drink coffee. Previous studies found no association between coffee drinkers and cancer. Caffeine has been found to be protective against type 2 diabetes in several research analysis.

Putting all the studies together, researchers conclude that moderate coffee consumption has several beneficial effects on health, but a high caffeine intake can increase the chance of growing larger tumours.