Among nutritional and/or environmental factors which may modify the risk of type 2 diabetes (T2D), coffee consumption has been associated for years with a decreased risk. However, epidemiological evidence on the association of habitual coffee consumption and the risk of T2D has been lacking.1-3
An exhaustive and systematic review of 13 cohort studies examined the association between coffee consumption and the onset of T2D.4Studies published from January 2001 to August 2011 including both men and women aged 20-88 were conducted in USA, Mexico, the Netherlands, Finland, Sweden, France, UK, Singapore, and Japan. Average follow-up duration for studies was 10 years, with a 6- to 7 year duration in four studies, and 18 years, for the longest performed in Sweden.
Among these cohorts, 1 247 387 participants were included, with 9 473 incident cases of T2D. The risk of diabetes was compared according to different degrees of coffee consumption. A decreased risk for new-onset T2D was found in subjects with the highest coffee consumption (more than 6 to 7 cups per day) compared with subjects with the lowest (less than 2 cups per day), with relative risks ranging from 0.39 (95% CI 0.24-0.64) to 0.80 (0.54-1.18). The strongest association observed may be explained by the importance in difference of coffee consumption between groups (more than 10 compared with less than 2 cups per day).5 The risk for incident T2D was also decreased in individuals with the second highest coffee consumption (4 to 6 cups per day) compared with subjects with the lowest one (less than 2 cups per day), with relative risks ranging from 0.45 (95% CI 0.23-0.90) to 0.93 (0.73-1.19). The reduction in T2D risk was higher when filtered coffee was compared with potboiled coffee, and when decaffeinated coffee was compared with caffeinated coffee.6 In one study, a strong inverse correlation between coffee consumption and risk for T2D was observed in individuals aged less than 60 years compared with those aged more than 60 years.7 The authors concluded that habitual coffee consumption is associated with a lower risk of T2D.
Only a few studies examining the potential relationship between coffee consumption and pathophysiological abnormalities responsible for T2D are available. In a nondiabetic adult cohort of nearly 1 000 participants from the Insulin Resistance Atherosclerosis Study (IRAS), cross-sectional associations between caffeinated and decaffeinated coffee consumption and insulin sensitivity and insulin secretion were examined.8After multiple adjustments, a positive correlation was found between caffeinated coffee intake and insulin sensitivity (P=0.04), but not with acute insulin response or proinsulin ratios. A positive correlation was found between caffeinated coffee intake and acute insulin response (P=0.0132), and an inverse correlation between caffeinated coffee intake and the ratios of both intact and split proinsulin to C-peptide (P=0.0148, andP= 0.0002, respectively). Caffeinated coffee thus appears to exert a favorable effect on insulin sensitivity, while decaffeinated coffee seems to improve b-cell function. While coffee does appear to have health benefits, further studies are needed to explain the protective effect of long-term coffee consumption against T2D onset.
Prof P-J. Guillausseau
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