Debate persists whether coffee is beneficial or problematic for human health. Coffee consumption has been associated with a decrease in risk of developing type 2 diabetes, and numerous epidemiological studies have demonstrated that healthy, habitual coffee drinkers are more protected from the risk of contracting diabetes than individuals who do not drink coffee. Coffee consumption has been associated with a reduced incidence of impaired glucose tolerance, hyperglycaemia and insulin sensitivity. Data suggest that several coffee components, such as chlorogenic acids, are involved in the health benefits of coffee. Various mechanisms for this protective effect have been proposed, including effects on incretin release, liver glucose metabolism and insulin sensitivity. Epidemiological data support numerous other health benefits for coffee, including reduced cardiovascular disease (CVD), a protective effect against some neurodegenerative conditions, a favourable effect on liver function and a protective effect against certain cancers. These associations are based mainly on observational studies and are currently insufficient to recommend coffee consumption as an interventional strategy for risk reduction in type 2 diabetes and other metabolic diseases. While excessive consumption can have adverse effects on some conditions, particularly in terms of sleep quality, these effects vary among individuals and most people do not have any symptoms from coffee drinking. Moderate coffee consumption is associated with no or little risk of severe diseases and may offer substantial health benefits. Thus, coffee is a safe, low-energy beverage and suitable for most adult people.
Editorial assistance was provided by Katrina Mountfort at Touch Medical Media.
Caffeine, chlorogenic acid, coffee, diabetes, Parkinson
Siamak Bidel has no conflicts of interest to declare. Jaakko Tuomilehto has received research funding for investigator-initiated research from the Institute for Scientific Information on Coffee, and has received travel and lecture fees from Programa de Promoción de Consumo Toma Café, Colombia.
April 10, 2012 Accepted:
May 20, 2013
Siamak Bidel, Hjelt Institute, Faculty of Medicine, University of Helsinki, PO Box 41 (Mannerheimintie 172, 6 krs.), FIN-00014 University of Helsinki, Finland. E: firstname.lastname@example.org
The publication of this article was funded by Mondelêz International, Inc. The views and opinions expressed are those of the authors and not necessarily those of Mondelêz International, Inc.
Coffee is a complex chemical mixture that contains many bioactive molecules. These include chlorogenic acid, polyphenols, methylxanthines including caffeine, carbohydrates, lipids, nitrogenous compounds, nicotinic acid, potassium and magnesium.1
With the exception of water, coffee is the most consumed beverage in the world and almost 500 billion cups are consumed annually. In 2007, Finland was the top coffee consuming country with 12 kg per capita.2
World coffee production for 2012–13 is forecast at a record high of 148 million bags.3
The impact of coffee on human health and disease has long been recognised: in the late-16th century it was observed that coffee accelerated digestion and increased the heart rate. A growing body of epidemiological research data suggests that coffee consumption may help prevent several chronic diseases, including type 2 diabetes, Parkinson’s disease and liver disease. This article aims to review epidemiological and clinical evidence for the impact of coffee on type 2 diabetes, and other aspects of human health.
Coffee Consumption and the Incidence of Type 2 Diabetes
Type 2 diabetes is one of the most serious global health concerns and its incidence is increasing: the total number of people with diabetes worldwide is projected to rise from 366 million in 2011 to 552 million by 2030.4
In 2012, type 2 diabetes imposed direct and indirect costs of an estimated $245 billion in the US.5
Given the high cost of diabetes in terms of both human lives and healthcare costs, the prevention of diabetes is vital. Developing interventions to prevent and manage type 2 diabetes depends on an understanding of the dietary and lifestyle factors that underlie the development of the disease.
Recent evidence suggests that coffee consumption is associated with a decreased risk of type 2 diabetes. The first epidemiological report indicating an inverse association between coffee consumption and type 2 diabetes dates back to 2002. A Dutch cohort study reported that participants drinking at least 7 cups of coffee per day were half as likely to develop type 2 diabetes compared with those who did not consume coffee.6
This finding has been supported by numerous cohort studies (see Table 1
). The association does not depend on race, gender or geographic distribution of the study population and is consistently observed, despite the fact that many of these studies reported that coffee consumption was associated with lifestyle factors that tend to be associated with an increased risk of cardiovascular and metabolic disease, such as smoking, high body mass index (BMI), low levels of physical activity and poor diet.
Two reviews have examined the body of data relating to type 2 diabetes risk and coffee consumption. A meta-analysis covering 457,922 individuals and 18 studies concluded that an inverse log-linear relationship exists between coffee consumption and subsequent risk of diabetes: each additional cup of coffee consumed per day is associated with a 7 % reduction in the excess risk of diabetes (relative risk [RR] 0.93 95 % confidence interval [CI] 0.91–0.95) after adjustment for potential confounders. Individuals consuming 3 to 4 cups of tea daily have a 28 % lower risk of type 2 diabetes.7
A systematic review of cohort studies (from January 2001 to August 2011) confirmed the association between coffee consumption and reduced risk of type 2 diabetes, and also found an advantage of filtered coffee over pot boiled, decaffeinated coffee over caffeinated coffee and a stronger inverse correlation in those aged less than 60 years.8
The inverse relationship between coffee consumption and type 2 diabetes remains when lifestyle factors are taken into account: analysis of a Finnish cohort study found that the risk of type 2 diabetes was reduced by half in obese and inactive individuals who consumed ≥7 cups of coffee daily compared with those who consumed <2 cups/day (see Figure 1
While cohort studies have provided a large body of evidence for the association of coffee consumption and diabetes risk, such studies have inherent limitations. Most studies employed selfreport questionnaires, which may be imprecise and prone to bias, such as different interpretations of the size of a cup of coffee, and use of milk and sugar. It is not possible to ascertain a cause–effect relationship entirely from observational data. Studies employing urinary or plasma biomarkers of coffee intake may provide a more accurate assessment of coffee intake.10
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