Drinking coffee may promote longevity in type 2 diabetes

Coffee can be a beneficial drink for patients with type 2 diabetes, with a recent meta-analysis finding moderate evidence that coffee can cut the risk of all-cause death.

Pooled data from 10 prospective cohort studies with 82,270 adult patients with type 2 diabetes showed that the highest category of coffee consumption conferred a 19-percent reduction in the risk of all-cause mortality as compared with the lowest consumption category (hazard ratio [HR], 0.81, 95 percent confidence interval [CI], 0.74–0.89). There was low evidence of heterogeneity (I², 36 percent; p_{heterogeneity}=0.12). [Nutr Metab Cardiovasc Dis 2021;31:2526-2538]

In a dose-response analysis, larger quantities of coffee seemed to be especially beneficial for preventing all-cause death. Relative to nonconsumption, drinking four cups of coffee daily lowered all-cause mortality by 21 percent (HR, 0.79, 95 percent CI, 0.72­–0.87; n=10 studies). There were also reductions observed for cardiovascular disease (CVD) mortality (HR, 0.60, 95 percent CI, 0.46–0.79; n=4), coronary heart disease (CHD) mortality (HR, 0.68, 95 percent CI, 0.51–0.91; n=3), CHD (HR, 0.72, 95 percent CI, 0.54–0.98; n=2), and total CVD events (HR, 0.77, 95 percent CI, 0.61–0.98; n=2).

“The inverse association of coffee drinking with all-cause mortality was significant independent of diabetes duration, degree of glycaemic control, and medications used,” according to the investigators.

“However, there was a reduction in the protective effect of coffee for consumption of >4 cups/day, which could be partially due to added sugar. For example, adding two teaspoons of sugar per cup of coffee and drinking 5 cups of coffee per day represents an intake of 50 g of added sugar per day, which far exceeds the recommendations,” they explained.

The certainty of evidence was graded moderate for all-cause mortality and low or very low for other outcomes. But the finding on the inverse association between coffee and all-cause mortality risk is consistent with those reported in previous meta-analyses in the general population. [Eur J Epidemiol 2019;34:731-752; Prev Med 2019;123:270-277; J Hum Nutr Diet 2019;32:279-287; Publ Health Nutr 2015;18:1282-1291]

As to why there was low evidence of heterogeneity between the studies, the investigators offered geographic region as a possible explanation for the observed inconsistency. “For the most part, type of coffee powder, methods used for roasting and brewing, and type of beverage used for coffee preparation may be different across the world.

“In addition, people may add different amounts of sugar and cream to coffee. Cup size may also be different. These differences may confound the association between coffee drinking and health outcomes across the world,” they pointed out.

Finally, there might have been a gender difference in haemodynamic effects of coffee in the body, as well as in pathophysiology and complications of type 2 diabetes, the investigators said. [Am J Cardiol 2004;93:1022-1026; Endocr Rev 2016;37:278-316]

The protective effects of coffee drinking against CVD and mortality in patients with type 2 diabetes may be related to caffeine or other components that exist in coffee, including minerals, phytochemicals, and antioxidants. [N Engl J Med 2020;383:369-378]

While coffee drinking has been reported to exacerbate insulin resistance, the detrimental effects of on insulin resistance generally occurs in short-term and coffee drinking has no adverse effects on glucose metabolism in long-term follow-up, the investigators said. [Diabetes Care 2002;25:364-369; J Tradit Complement Med 2018;9:184-191]

Despite the presence of several study limitations, the overall findings indicate that coffee drinking is accompanied by a series of long-term health benefits that could outweigh the short-term adverse effects on insulin resistance, they added.