Review
Coffee and type 2 diabetes: From beans to beta-cells

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Abstract

Coffee consumption has been associated with improved glucose tolerance and a lower risk of type 2 diabetes in diverse populations in the U.S., Europe, and Japan. This review discusses the strength of the evidence, relevant mechanisms, possible implications, and directions for further research. The finding that higher consumption of decaffeinated coffee was associated with a lower risk of type 2 diabetes suggests that coffee constituents other than caffeine play a role. Coffee is a source of several compounds that improved glucose metabolism in animal studies, including the chlorogenic acids and lignans. Further research on phytochemicals in coffee may lead to the identification of novel mechanisms for effects of diet on the development of type 2 diabetes. In addition, knowledge on effects of coffee components may aid in the development or selection of types of coffee with improved health effects. Longer-term randomized intervention studies that test the effects of coffee consumption on glucose tolerance are warranted. Physical activity and weight management should be the mainstay of public health strategies to prevent type 2 diabetes. For individual choices regarding coffee consumption, potential effects of coffee on various health outcomes should be considered.

Introduction

The importance of primary prevention of type 2 diabetes is increasingly recognized, and this has stimulated an interest in the role of dietary factors in the etiology of type 2 diabetes. Until recently, research on dietary factors and risk of type 2 diabetes has mostly focused on macronutrients [1]. However, micronutrients and phytochemicals may also affect glucose metabolism [2]. In 2002, results from a Dutch cohort study on coffee consumption and risk of type 2 diabetes were reported. Participants who consumed 7 or more cups of coffee per day were 0.50 (95% confidence interval [CI] 0.35–0.72) times as likely to develop type 2 diabetes as compared with those who consumed 2 or fewer cups per day [3]. This finding was followed by the rapid publication of the results of more than 15 epidemiological studies on habitual coffee consumption in relation to insulin sensitivity, hyperglycemia and risk of type 2 diabetes in various countries [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. In this review, I will briefly discuss the strength of the evidence for a relation between higher coffee consumption and a lower risk of type 2 diabetes. Furthermore, I will describe suggested mechanisms for effects of coffee components on glucose metabolism, give suggestions for further research, and discuss possible implications for public health.

Section snippets

Coffee consumption and risk of type 2 diabetes

Studies on coffee consumption and risk of type 2 diabetes have been reviewed systemically [20]. Nine cohort studies on coffee consumption and risk of type 2 diabetes included a total of 193,437 participants and 8394 incident cases of type 2 diabetes. The summary multivariate-adjusted relative risk (RR) of type 2 diabetes was 0.65 (95% CI 0.54–0.78) for the highest (≥6 or ≥7 cups per day) and 0.72 (95% CI 0.62–0.83) for the second highest (4–6 cups per day) category of coffee consumption

Mechanisms

Table 2 shows a selection of coffee components [24], [25], [26] and suggested mechanisms for effects of these components on glucose metabolism [27], [28], [29], [30], [31], [32], [33], [34], [35]. Most data on effects of coffee components on glucose metabolism are based on animal and in vitro studies, and the relevance for the development of type 2 diabetes in humans is currently unclear. However, the results suggest that an effect of coffee consumption on glucose metabolism is biologically

Suggestions for further research

Two types of studies seem to be priorities for further research in the area of coffee consumption and glucose metabolism. First, a longer-term randomized trial of coffee consumption with appropriate outcome measures is warranted. The inverse associations between decaffeinated coffee and risk of type 2 diabetes in cohort studies suggest that the inclusion of an intervention with decaffeinated coffee would be worthwhile. Outcome measures should not be solely based on measurements in fasting blood

Relevance for public health

Increased physical activity and weight management should be the mainstay of public health strategies to prevent type 2 diabetes. The beneficial effects of physical activity and weight management are not limited to type 2 diabetes, but can also lower the risk of cardiovascular diseases, various types of cancer, and premature mortality [66], [67], [68], [69].

For choices of individuals regarding coffee consumption the potential effect of coffee consumption on risk of type 2 diabetes can be taken

Acknowledgement

R.M.v.D. is partly supported by the Netherlands Organization for Scientific Research (ZonMw VENI grant No. 916.46.077).

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