reprinted from DiabetesWatch, a publication of the Philippine Diabetes Association, January-April 2007
Recent yeas have seen the proliferation of coffee shops all over the country. What does this have to do with diabetes? Plenty. ..if the findings of a large prospective study is to be believed.
As reported in the November 2006 issue of Diabetes Care, the study confines itself to the consumption of pure coffee -- without the additives which coffee shops offer. Given this caveat, what does the study conclude? That coffee consumption reduces the risk for Type 2 diabetes by 60 per cent compared with those who didn't drink coffee.
The study took place between 1984-1987 and 1992-1996. The investigation followed up 910 adults aged 50 years or older without diabetes at the start of the study, through history and oral glucose tolerance test (where blood sugars are obtained before and after the intake of a pure glucose solution).
They were followed up for eight years after assessment of coffee intake, when they were made to undergo another glucose tolerance test.
- Past and current coffee drinkers were found to have a lower risk for "incident diabetes" (no diabetes at the start of the study, and a positive glucose tolerance test at the end of the study).
- About 300 participants who had glucose abnormalities at the start of the study not falling in the category of daibetes (blood sugar levels between the normal and the diabetic values, or impaired category) did not proceed to manifest diabetes at the end of the study.
The results in coffee drinkers were compared with those of subjects who never drank coffee during the study. The authors conclude that "the study confirms a striking protective effect of caffeinated coffee against incident diabetes and extends these findings to incident diabetes based on OGTT (oral glucose tolerance test) independent of multiple plausible confounders."
Previous studies had reported the beneficial effects of coffee drinking, but these studies didn't use the oral glucose test to confirm the absence or presence of diabetes.
Nobody yet knows the exact way in which coffee confers its protection against the development of diabetes. A study by Wu and colleagues (Diabetes Care, June 2005) showed that coffee reduces the C-peptide levels in coffee drinkers, especially in overweight and obese American women. C-peptide is a marker for insulin secretion and for insulin levels in the blood, as it is co-secreted with insulin by the beta cells of the pancreas.
Too much C-peptide (and therefore of insulin) in the blood suggests that the beta cells are overproducing insulin, because the tissues are not responding to normal levels -- a state of insulin resistance. When this happens, there will come a time when the beta cells will become exhausted, and their ability to produce insulin (or C-peptide) will diminish and diabetes ensues.
Thus, low levels of C-peptide suggest that the tissues have regained their normal sensitivity to insulin, and could therefore prevent diabetes, if there was insulin resistance before, such as what exists in overweight and obese individuals.
Several questions come up: is the degree of protection against diabetes related to the amount of coffee consumed? There seems to be no relationship between the nuber of cups drunk and the protection against diabetes.
Is this benefit related to the kind of coffee? Arabic coffee beans are the preferred coffee bean variety in most countries, whereas robusto is the choice of drinkers in France, Italy, Portugal and the UK. There is less diabetes in the latter countries as compared to the rest of the world
Is the protection against diabetes related to the way the coffee is prepared? Two Finnish studies suggest that drip filtered coffee seems to be more protective against diabetes.
Do all caffeinated drinks impart the same protection as coffee? The 2005 study showed that C-peptide was reduced with the ingestion of both caffeinated or decaffeinated coffee. However, tea did not reduce C-peptide.
How long does one have to drink coffee to get the benefit of protection against diabetes? Consumption must be chronic, i.e., at least one year.
What in coffee protects against diabetes? The 2005 study showed that it isn't caffeine, because the effect was achieved with decaf. Whatever it is that reduces diabetes risk must reside in other compounds in coffee, and the candidates include quinides, trigonelline and chlorogenic acid, which is a particularly strong antioxidant. It's possible that antioxidants improve insulin sensitivity in human Type 2 diabetes and decrease insulin levels in rats. Chlorogenic acid may combine with other antioxidants in coffee to decrease oxidative stress.
Care for another cup of coffee?