Background: Recent studies have shown that caffeine consumption adversely affects blood glucose control in type 2 diabetes (T2DM)1, but that it does not increase mortality in men with T2DM and no prior cardiovascular disease2.
Aim: To examine the prevalence of caffeinated beverage consumption in Australians with T2DM and its effect on all-cause death.
Patients and Methods: The longitudinal Fremantle Diabetes Study Phase II (FDS2) includes 1551 patients with T2DM recruited from 2008 to 2011. Detailed baseline assessment included self-reported frequency of tea, coffee and caffeinated soft drink consumption. The cohort was followed to death/census at end-March 2014.
Results: The participants were of mean±SD age 65.7±11.6 years, 51.9% were male, and their median [inter-quartile range] diabetes duration was 9.0 [3.0-15.9] years. Caffeine consumption was ascertained in 1496 (96.5%), of whom 114 drank none, 986 drank ≥ 1 cup of tea/day, 970 drank ≥1 cup of coffee/day, and 154 (10.3%) drank ≥1 soft caffeinated drink/day. During 4.3±1.2 years of follow-up, 161 (10.4%) died. Those who died were older at study entry (74.2±13.4 vs 64.7±11.3 years, P<0.001), had longer diabetes duration (15.6 [6.0-20.2] vs 8.0 [2.2-15.1] years, P<0.001) and were more likely to be insulin-treated (33.5% vs 21.3%, P=0.001). Cox proportional hazards modelling with age as the time-line showed that all-cause mortality was predicted by male sex, Aboriginality, current smoking, eGFR category and anaemia, while being married/in a de facto relationship was protective. After adjusting for this most parsimonious model, the number of caffeinated soft drinks predicted mortality (hazard ratio (95% CI): 1.37 (1.12-1.66) per drink, P=0.002). Drinking ≥5 caffeinated soft drinks/day increased the risk 8-fold. Coffee and tea consumption did not predict mortality.
Conclusions: Although tea/coffee consumption is safe, caffeinated soft drink consumption is an adverse prognostic indicator that should be considered when dietary advice is provided to Australians with T2DM.