Coffee consumption and risk of type 2 diabetes mellitus

Abstract

In their report on the protective effects of coffee drinking on type 2 diabetes mellitus, Rob van Dam and Edith Feskens (Nov 9, p 1477)1van Dam RM Feskens EJM Coffee consumption and risk of type 2 diabetes mellitus.Lancet. 2002; 360: 1477-1478Summary Full Text Full Text PDF PubMed Scopus (386) Google Scholar overlook a potential confounding factor: additives to coffee. Our ever-expanding café culture provides endless permutations of types of coffee, ranging from fat content and proportion of milk to type of flavouring and the amount and type of sugar added. Although van Dam and Feskens adjust for body-mass index, and therefore to some extent the cumulative glucose burden, the direct physiological and pathogenic effects of multiple divided glucose loads (in coffee) should not be overlooked.The investigators report a halving in the probability of progression to type 2 diabetes mellitus in individuals who drank more than seven cups of coffee a day compared with those who drank two cups or fewer in a day. They suggest that the metabolic effects of components in coffee, such as chlorogenic acid and magnesium, might explain this finding. However, van Dam and Feskens take no account of the calorific or glucose content of the participants' coffee. Hence, a source of substantial variability might be differences in coffee-drinking habits— for example, the ardent coffee enthusiast who drinks seven cups of black coffee without sugar compared with the social coffee drinker who adds full-fat cream and two lumps of sugar to his daily cup. Such a range of glucose burdens contribute to varying extents of hyperglycaemia and affect progression to type 2 diabetes mellitus and β-cell failure, possibly due to glucotoxicity.2Olefsky JM Kruszynska YT Type 2 diabetes mellitus: etiology, pathogenesis, and natural history.in: 4th edn. Endocrinology. WB Saunders, Philadelphia2001: 776-797Google Scholar Furthermore, the excesses in glucose and free fatty acids in full-fat, sweetened coffee could negate any beneficial effects on glucose metabolism that might be conferred by its contents.Given the variability in glucose and free fatty acid content in coffee, irrespective of the number of cups ingested, it is impossible to derive advice about diabetes prevention from the results of this study. Moreover, van Dam and Feskens do not elaborate on the health risks associated with excessive coffee drinking, which may well militate against any real benefit of seven cups of coffee a day. In their report on the protective effects of coffee drinking on type 2 diabetes mellitus, Rob van Dam and Edith Feskens (Nov 9, p 1477)1van Dam RM Feskens EJM Coffee consumption and risk of type 2 diabetes mellitus.Lancet. 2002; 360: 1477-1478Summary Full Text Full Text PDF PubMed Scopus (386) Google Scholar overlook a potential confounding factor: additives to coffee. Our ever-expanding café culture provides endless permutations of types of coffee, ranging from fat content and proportion of milk to type of flavouring and the amount and type of sugar added. Although van Dam and Feskens adjust for body-mass index, and therefore to some extent the cumulative glucose burden, the direct physiological and pathogenic effects of multiple divided glucose loads (in coffee) should not be overlooked. The investigators report a halving in the probability of progression to type 2 diabetes mellitus in individuals who drank more than seven cups of coffee a day compared with those who drank two cups or fewer in a day. They suggest that the metabolic effects of components in coffee, such as chlorogenic acid and magnesium, might explain this finding. However, van Dam and Feskens take no account of the calorific or glucose content of the participants' coffee. Hence, a source of substantial variability might be differences in coffee-drinking habits— for example, the ardent coffee enthusiast who drinks seven cups of black coffee without sugar compared with the social coffee drinker who adds full-fat cream and two lumps of sugar to his daily cup. Such a range of glucose burdens contribute to varying extents of hyperglycaemia and affect progression to type 2 diabetes mellitus and β-cell failure, possibly due to glucotoxicity.2Olefsky JM Kruszynska YT Type 2 diabetes mellitus: etiology, pathogenesis, and natural history.in: 4th edn. Endocrinology. WB Saunders, Philadelphia2001: 776-797Google Scholar Furthermore, the excesses in glucose and free fatty acids in full-fat, sweetened coffee could negate any beneficial effects on glucose metabolism that might be conferred by its contents. Given the variability in glucose and free fatty acid content in coffee, irrespective of the number of cups ingested, it is impossible to derive advice about diabetes prevention from the results of this study. Moreover, van Dam and Feskens do not elaborate on the health risks associated with excessive coffee drinking, which may well militate against any real benefit of seven cups of coffee a day. Coffee consumption and risk of type 2 diabetes mellitusAuthors' reply Full-Text PDF