Coffee is amongst the most widely consumed beverages in the world. Most of the evidence indicates a strong inverse association between coffee consumption and diabetes. Caffeine has been studied more than any other ingredient in coffee, but coffee contains many different substances. Some studies show caffeinated and decaffeinated coffee as having the same effect, which suggests that something else in coffee is responsible for its beneficial effects.
Physiological role of coffee on glucose metabolism
The health effects of coffee have been associated with its caffeine content. Caffeine has been shown to acutely reduce sensitivity to insulin, but also seems to have beneficial effects. Results of research suggest that an effect of coffee consumption on glucose metabolism is biologically plausible, and that the effects of coffee cannot be equated with those of caffeine. Other bioactive ingredients of coffee are: chlorogenic acid and quinides, magnesium, lignans (are a group of chemical compounds found in plants) and other micronutrients (van Dam 2004). Table 1 shows a selection of coffee components and suggested mechanisms for effects of these components on glucose metabolism.
|Component a||Suggested mechanisms|
|Caffeine||Reduced glucose storage through increased released of epinephrine or antagonism of the adenosine receptor|
|Increased expression of uncoupling proteins and lipid oxidation|
|Chlorogenic acids and quinides||Antioxidant properties|
|Reduction of hepatic glucose output through inhibition of glucose-6-phosphatase|
|Effects on soft tissue mineral composition through action as a metal chelator|
|Reduction of intestinal glucose absorption through inhibition of glucose-6-phosphate translocase 1 and other mechanisms, and a subsequent increase in GLP-1 levels|
|Magnesium||Cofactor for enzymes involved in phosphorylation that are essential for glucose metabolism; may affect insulin receptor activity through effects on hormone-receptor affinity or membrane viscosity|
|Lignans||Antioxidant action and effects through binding of estrogen receptors, after conversion to enterodiol and enterolactone|
[ a Reference provides information on the concentration of the component in coffee]
Clinical evidence for coffee and diabetes
Prevention of diabetes
The first study of coffee consumption and risk of type 2 diabetes was reported by Dutch researchers in the Lancet in 2002. They prospectively investigated the association between coffee consumption and risk of clinical type 2 diabetes in a population-based cohort of 17,111 Dutch men and women aged 30–60 years. During 125,774 person years of follow-up, 306 new cases of type 2 diabetes were reported. After adjustment for potential confounders, individuals who drank at least seven cups of coffee a day were 0•50 (95% CI 0•35–0•72, p=0•0002) times as likely to develop type 2 diabetes as those who drank two cups or fewer a day.
In 2009 Huxley et al published a meta-analysis on the association of coffee and decaffeinated coffee consumption with risk of diabetes. They found an inverse log-linear relationship between coffee consumption and subsequent risk of diabetes such that every additional cup of coffee consumed in a day was associated with a 7% reduction in the risk of diabetes after adjustment for potential confounders. Similar significant and inverse associations were observed with decaffeinated coffee and tea and risk of incident diabetes.
After this this meta-analysis, more studies have been published which confirmed the negative association for coffee consumption and type 2 diabetes with a dose response relation: lower incidence at higher consumption.
Effects of coffee on diabetes related complications
Most studies refer to the role that coffee can play in the primary prevention of diabetes. There is some data on the possible influence of coffee consumption on the complications of diabetes.
Bidel et al did a large prospective study among almost 4000 Finnish patients with type 2 diabetes aged 25 to 74 years to assess the association between coffee consumption and CVD mortality among patients with type 2 diabetes. During the average follow-up of 20.8 years, the respective multivariate-adjusted hazard ratios in participants who drank 0-2, 3-4, 5-6, and > or =7 cups of coffee daily were 1.00, 0.77, 0.68 and 0.70 for total mortality (P<0.001 for trend), 1.00, 0.79, 0.70 and 0.71 for CVD mortality (P=0.006 for trend), 1.00, 0.78, 0.70 and 0.63 for CHD mortality (p=0.01 for trend), and 1.00, 0.77, 0.64 and 0.90 for stroke mortality (p=0.12 for trend). They concluded that in type 2 diabetic patients coffee drinking is associated with reduced total, CVD and CHD mortality.
Zangh et al did two prospective cohort studies to investigated coffee consumption in relation to risk of CVDs and mortality in diabetic women and men. These data indicate that regular coffee consumption is not associated with increased risk for CVD or mortality in diabetic women and men.
Conclusion and discussion
A number of studies demonstrate an association between (moderate) coffee consumption and reduced risk of developing type 2 diabetes and maybe the macrovascular complications of this disease. This can have implications in light of the already high and increasing prevalence of type 2 diabetes.
The choice of appropriate types of coffees may lead to benefits with regard to glucose metabolism while avoiding some of the potential detrimental health effects of coffee. Consumption of decaffeinated coffee may provide benefits for reduction of risk of type 2 diabetes while avoiding the detrimental effects of caffeine (for example reduced sleep quality). Further knowledge on the effects of different coffee constituents on development of diabetes and its complications is necessary. The underlying mechanisms likewise need further investigation.
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