What other factors might be behind the association?
A number of additional research papers have tried to answer this question.
The effect of certain genetic polymorphisms (the existence of several alternative DNA states, or alleles, at a defined position in the genome, or locus) on associations between coffee intake and type 2 diabetes was considered in a 2016 review, suggesting that the evidence for a reduced risk of type 2 diabetes in coffee drinkers may be limited when taking into account the genetic profile43. A 2020 pooled analysis did not find any associations between genetic polymorphisms and type 2 diabetes44.
Additions to coffee
Research in a group of pre-diabetic patients concluded that diabetes progression was lowest in patients who drank black coffee three or more times per day. The study also considered the impact that typical additions to coffee, like creamer and sugar, had; and concluded that whilst the risk was lower for the patients who typically consumed black coffee than for those who mixed creamer and sugar into their coffees, the difference was not significant29.
Research has suggested that coffee could partly inhibit postprandial hyperglycemia, and in turn may prevent the occurrence of type 2 diabetes41. A later study suggested that the time of drinking coffee may play a distinct role in glucose metabolism, with the authors reporting the strongest association for coffee consumed at lunchtime19.
According to a cross-sectional multi-ethnic study amongst 954 non-diabetic adults, the effect of caffeinated coffee was positively related to insulin sensitivity and decaffeinated coffee was favourably related to pancreatic beta-cell function46. However, a randomised control study suggested that consuming 4 cups of caffeinated coffee a day for 24 weeks had no significant effect on insulin sensitivity or biological mediators of insulin resistance47.
Caffeine in those with diagnosed diabetes
A retrospective study, published in 2018, considered the effect of caffeine consumption in a group of patients already diagnosed with diabetes (both type 1 and type 2). The results suggested that caffeine from coffee was associated with a reduced all-cause mortality in women but not in men. The authors concluded that further research is required to understand the effect of caffeine consumption in men and women with diabetes in more detail48.
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