Diabetes is an increasing health problem worldwide. Approximately 11.3 precent of US adults have type-2 diabetes. Keeping in mind that diabetes is such a strong risk factor for cardiovascular disease, it is likely that the burden of heart disease and stroke in our community will increase in the near future. Therefore, in order to imply preventive measures, an understanding of the underlying causes of the diabetes epidemic is hugely important. Several epidemiological studies have shown that habitual caffeine consumption, in the form of tea and coffee is associated with less risk of diabetes. However, this has been confounded by some short term metabolic studies showing that caffeine may elevate blood sugar levels and decrease insulin sensitivity. Both these effects might in theory increase the risk of diabetes. An analysis of huge epidemiological data, published in the most recent issue of the American Journal of Clinical Nutrition has highlighted the association of caffeinated and decaffeinated coffee and tea consumption on the risk of type-2 diabetes. Furthermore, the researchers investigated the joint effects of caffeine and sugar-sweetened beverages and caffeine and coffee on the risk of type-2 diabetes.
Bhupathiraju and colleagues at The Harvard Public School of Health used data from the Nurses Health Study (NHS) and the The Health Professionals Follow-up Study (HPFS) to study the effects of caffeinated and caffeine free beverages on the risk of developing type-2 diabetes among women and men. The consumption was based on repeated food frequency questionnaire (FFQ). Participants were asked how often on average during the previous year they had consumed caffeinated and decaffeinated coffee, and different types of sugar-sweetened and artificially sweetened carbonated beverages. Carbonated beverages included caffeinated and caffeine-free colas and carbonated soft drinks. The caffeine content was estimated to be 137 mg per cup of coffee, 47 mg per cup of tea, and 46 mg per bottle or can of cola beverage. Follow-up was for 24 years, between 1984 and 2008.
These were the main findings of the study
- There were about 10 thousand cases of diabetes registered among more than 172 thousand participants.
- After major lifestyle and dietary risk factors were controlled for, intake of caffeinated and caffeine-free sugar-sweetened beverages was significantly associated with a higher risk of type-2 diabetes
- Caffeine-free artificially sweetened beverages were associated with increased risk of type-2 diabetes among the women but not men
- The consumption of caffeinated and decaffeinated coffee was associated with a lower risk of type-2 diabetes
- Caffeinated tea was associated with a lower risk of type-2 diabetes among women
- Substitution of caffeinated carbonated beverages with other caffeinated beverages such as coffee and tea was associated with lower risk of type-2 diabetes
What can we learn from the study?
Not surprisingly, the consumption of sugar sweetened beverages, irrespective of the caffein content, appears to increase the risk of diabetes. Other studies have indicated that sugar-sweetened beverages are associated with weight gain, the metabolic syndrome and type-2 diabetes. The study also indicates that drinking artificially sweetened beverages may increase the risk of diabetes in some groups, although the association appears weaker than for sugar-sweetened beverages. The latter are sweetened with sucrose or high-fructose corn syrup, both of which rapidly increase blood sugar and insulin concentration.
Drinking coffee, both caffeinated and decaffeinated was associated with lower risk of diabetes. According to the study results, a risk reduction of 4 to 8 percent in incident type-2 diabetes may be expected for every 1-cup increment in coffee consumption. The authors propose several possible mechanisms to explain the protective effects of tea and coffee on the risk of developing diabetes. Tea contains flavonoids, an antioxidant that may inhibit oxidative stress associated with the risk of diabetes. Coffee is rich in chlorgenic acid, an antioxidant which may improve glucose metabolism.
The main conclusion is that while the consumption of soft drinks, in particular those that are sugar-sweetened, appear to increase the risk of developing diabetes, drinking coffee and tea seems to lessen the risk. However, whether the coffee contains caffeine or not appears unimportant in this respect.