Pereira and colleagues1 found an inverse association between coffee consumption and the risk of type 2 diabetes mellitus. Because this relation was stronger for decaffeinated coffee intake, it is likely that constituents other than caffeine are involved in this beneficial association. We suggest that some of the involved mechanisms might be related to inhibition of iron absorption by polyphenol compounds present in coffee, be it regular coffee or decaffeinated coffee. The main phenolic compound in coffee, chlorogenic acid, is a potent inhibitor of nonheme iron absorption.2,3 Hurrell et al3 report that the polyphenolic content typical in a cup of instant coffee reduces iron absorption from a test meal by 60% to 90%. Among elderly participants in the Framingham Heart Study,2 each 236 mL/wk (1 cup per week) of coffee consumed was associated with 1% lower serum ferritin concentration.
Mascitelli L, Pezzetta F, Sullivan JL. Inhibition of Iron Absorption by Coffee and the Reduced Risk of Type 2 Diabetes Mellitus. Arch Intern Med. 2007;167(2):204-205. doi:10.1001/archinte.167.2.204-b