Coffee and Diabetes – The Harvard Study

One of the earlier studies on the correlation between coffee consumption and Type 2 diabetes was carried out at the Harvard School of Public Health and Brigham and Women’s Hospital. The results of the study were published in the January 6, 2004 issue of the Annals of Internal Medicine. In a study that had over 125,000 participants, researchers found that drinking six or more cups of coffee a day significantly reduces the risk of developing Type 2 diabetes.

The researchers used information gathered by two well-known studies – the ongoing Health Professionals Follow-up Study and the Brigham and Women’s Nurses Health Study. Each of the studies tracks multiple health, food and lifestyle factors in health professionals via periodic questionnaires. The results compiled in the two studies have been the basis for a great deal of health-related research because they represent two of the largest sample groups of any questionnaire based study, and because of the length of time that the information has been being compiled.

The Health Professionals Study tracked 41,934 men for 12 years – 1986 to 1998. The Brigham and Women’s Nurses Health study tracked 84,276 women for eighteen years – from 1980 to 1998. The researchers used food frequency questionnaires every two to four years to track participants’ intake of both regular and decaffeinated coffee.


Over the course of the study, 1,333 men and 4,058 women were diagnosed with type 2 diabetes. After filtering out other lifestyle factors like smoking, exercise and obesity, researchers found that men who drank six or more cups of caffeinated coffee each day reduced their risk of type 2 diabetes by 50%. Among women, those who drank six or more cups of caffeinated coffee per day reduced their risk of developing type 2 diabetes by 30%. In both cases, the calculations were made against groups that didn’t drink coffee at all. The study also found that those who drink decaffeinated coffee also reduce their risk of developing type 2 diabetes, but to a far lesser extent than those who drink caffeinated coffee.

While we often consider coffee and caffeine to be nearly synonymous, researchers note that coffee has a lot of antioxidants like chlorogenic acid and magnesium. Those can actually improve insulin sensitivity, which may be part of the reason for the lowered risk.

These results have since been further confirmed by other studies with similar results. Despite the further studies, most researchers still feel that more research is needed before they make any firm statements about drinking coffee and diabetes. As the author of the Harvard study stated at the time the results were released, “We still don’t know exactly why coffee is beneficial for diabetes. It doesn’t mean everyone should run out for a latte.”