Coffee has not generally been considered a health drink. It has been associated health issues like high blood pressure, heart risk, and general jitteriness. Nowadays, however, coffee is strongly linked to a number of health benefits, including reduced risk for diabetes and certain forms of cancer. And since decaf provides many of the same benefits, caffeine doesn’t seem to be the key.

Now, two new studies have found that increased coffee consumption is strongly connected to reduced risk of certain breast cancers in women and a lower risk for fatal prostate cancer in men.

Reducing ER-Negative Breast Cancer

The first study, led by Jingmei Li, looked at the incidence of breast cancer in almost 6,000 menopausal women, about half of whom suffered from some form of breast cancer. The researchers gave the women detailed questionnaires about their lifestyle and eating habits, including how much coffee they tended to drink. Questions also probed at other personal habits, like how much alcohol the women consumed, their exercise routines, whether or not they took hormone replacement therapy (HRT), and their smoking status.

The researchers found that women who drank at least 5 cups of regular coffee per day had a "strong reduction" in estrogen receptor (ER)-negative breast cancer. A reduction in ER-positive forms of breast cancer, those that are sensitive to the female sex hormones, was not found.

The researchers found that women who drank at least 5 cups of regular coffee per day had a "strong reduction" in estrogen receptor (ER)-negative breast cancer. Breast cancer is classified as being either responsive or unresponsive to the female sex hormones, estrogen and progesterone. In the current study, ER-negative and progesterone receptor (PR)-negative forms were found to be lower in women who consumed the 5 cups per day — 57% and 33%, respectively. A reduction in ER-positive forms of breast cancer, those that are sensitive to the female sex hormones, was not found.

While the authors write that their results "support a protective effect of high intakes of coffee against ER-negative breast cancer," it is important to remember that the study did not show causal relationship between coffee and breast cancer risk, only a correlation between the two.

What compound in coffee is responsible for the reduced risk? The authors of the article write that although only caffeinated coffee was considered here, "caffeine is only one out of the many different compounds contained in coffee," so other candidates should be addressed. For instance, coffee contains many different polyphenols, plant-derived compounds that can act as antioxidants, scavenging for free radicals and repairing the cell damage that free radicals bring about. It also contains phytoestrogens, plant-based chemicals that mimic the effects of estrogen; different phytoestrogens have been found to have different effects on ER-positive vs. ER-negative forms of breast cancer, making phytoestrogens a likely candidate.

Brewing method may have something to do with coffee’s cancer-fighting abilities: another recent study found that boiled coffee had an effect on breast cancer risk, but filtered coffee did not.

On a potentially related note, the authors point out that the brewing method may have something to do with coffee’s cancer-fighting abilities: another recent study found that boiled coffee had an effect on breast cancer risk, but filtered coffee did not. Whether brewing method affects the mixture of the healthy and harmful compounds in coffee will definitely need attention in future studies.
Reducing Lethal Prostate Cancer, Too

Coffee doesn’t only affect cancer risk in women — it reduces certain prostate cancer in men. In a second study, led by Kathryn Wilson, men who drank at least 6 cups of coffee per day had an 18% reduced risk of developing prostate cancer overall, though this effect was not statistically significant, meaning that it could have been due to chance.

Men who drank at least 6 cups had a significant 60% reduced risk of having a fatal form of prostate cancer. Even men who drank a just few cups of coffee a day – caffeinated or decaffeinated – had a reduced rate of fatal prostate cancer. Coffee consumption did not seem to have an effect on milder forms of prostate cancer.

Coffee has been shown to improve the body’s use of glucose, affect levels of sex hormones, and contain many types of phytochemicals that act as antioxidants and anti-inflammatory compounds — any or all of which could explain coffee’s effect on prostate cancer.

Were coffee drinkers just healthier men in general? It’s unlikely, since coffee intake was also associated with eating more calories overall (including processed meat) and with smoking. Therefore, the effect seems to be due to the coffee itself, though it’s still unknown what the exact chemicals are that possess the cancer-fighting benefits. Because similar results were found for both caffeinated and decaffeinated coffee, again it seems that caffeine is not the answer. The authors of the study point out that coffee has been shown to improve the body’s use of glucose, affect levels of sex hormones, and contain many types of phytochemicals that act as antioxidants and anti-inflammatory compounds — any or all of which could explain coffee’s effect on prostate cancer.

Since drinking too much coffee does pose some health risks, upping your coffee intake is probably not a good idea at this time until researchers learn more about how it works in the body, especially regarding cancer risk. After all, neither study showed cause and effect — just a link between two variables.

Dr. Li, the author of the first study reminds us that her study’s results do not mean that the connection between coffee and breast cancer "is a cause-and-effect relationship, only that the two factors are somehow related… Until we find out exactly what in coffee leads to a change in breast cancer risk, I won't go running to my neighbours to encourage them to change their coffee drinking habits." So sticking with your normal coffee-drinking routine is probably safe, if you’ve found a level that works for you. As always, talk to your doctor if you have any concerns about whether what you’re putting in your body is right for you.

The first study was carried out by a team at the Karolinska Institute in Stockholm, and published in the May 11, 2011 issue of Breast Cancer Research. The second study was conducted by a team at the Harvard School of Public Health, and published in the May 17, 2011 issue of Journal of the National Cancer Institute.