Greater Green Tea, Coffee Consumption Associated With Lower Mortality Risk in T2D Population

Higher consumption of green tea and coffee was associated with reduced all-cause mortality among individuals with type 2 diabetes (T2D), according to the results of a prospective study published in BMJ Open Diabetes Research and Care. The combined effect appeared to be additive in this patient population.

Despite recent advancements in pharmacological treatments for T2D, lifestyle improvements are still regarded as basic therapy for the disease. However, no studies have yet investigated the association between green tea consumption and mortality in patients with T2D.

"Through antioxidant, anti-inflammatory, or anti-bacterial properties, higher green tea consumption has been reported to confer health benefits, including preventing such chronic diseases as diabetes mellitus, and reduce mortality,” the researchers wrote.

In addition, coffee contains bioactive chemicals that have been reported to impact health through various mechanisms.

To investigate the combined effect of green tea and coffee consumption on mortality, researchers in Japan analyzed data from the Fukuoka Diabetes Registry. This multicenter prospective study includes patients who regularly attended teaching hospitals certified by the Japan Diabetes Society or certified diabetes clinics in Fukuoka, Japan, between April 2008 and October 2010.

Nearly 5000 individuals (N = 4923) with T2D were followed prospectively for a median of 5.3 years. The mean patient age was 66 years, and a majority (n = 2790) were male. Patients reported data on smoking habits, alcohol intake, sleep duration, and additional lifestyle behaviors via a self-administered questionnaire. A total of 309 patients passed away during follow-up.

Using data gleaned from another self-administered diet history questionnaire, the researchers classified patients into 4 groups, by beverage:

1. Green tea: none, ≤1 cup/day, 2-3 cups/day, ≥4 cups/day
2. Coffee: none, <1 cup/day, 1 cup/day, ≥2 cups/day

No questions were asked on the consumption of decaffeinated or caffeinated beverages, as decaffeinated drinks are uncommon in Japan.

For green tea consumption, multivariable-adjusted HRs for all-cause mortality were (P for trend = .002):

• None: 1.0 (referent)
• ≤1 cup/day: 0.85 (95% CI, 0.60-1.22)
• 2-3 cups/day: 0.73 (95% CI, 0.51-1.03)
• ≥4 cups/day: 0.60 (95% CI, 0.42-0.85)

For coffee, hazard ratios were (P for trend = . 002):

• None: 1.0 (referent)
• <1 cup/day: 0.88 (95%, 0.66-1.18)
• 1 cup/day: 0.81 (95%, 0.58-1.13)
• ≥2 cups/day: 0.59 (95%, 0.42-0.82)

For combined coffee and green tea, hazard ratios were:

• No consumption of green tea and coffee: 1.0 (referent)
• 2-3 cups/day of green tea with ≥2 cups/day of coffee: 0.49 (95% CI, 0.24-0.99)
• ≥4 cups/day of green tea with 1 cup/day of coffee: 0.42 (95% CI, 0.20-0.88)
• ≥4 cups/day of green tea with ≥2 cups/day of coffee: 0.37 (95% CI, 0.18-0.77) for

The impact of each beverage on mortality was independent, while similar trends were also present in analyses of cardiovascular disease–specific mortality. Overall, “the combination of higher green tea and coffee consumption significantly reduced all-cause mortality risk by 63%.”

Mechanisms accounting for the association are not yet understood. Caffeine may contribute to the relationship; however, previous studies found consumption of both caffeinated and decaffeinated coffee were associated with reduced mortality. Furthermore, the researchers found “the relative risk reduction of mortality (HR, 0.37) was greater than when consuming only green tea (HR, 0.72) or only coffee (HR, 0.76). Thus, the protective mechanisms of the 2 beverages may differ.”

The investigators did not analyze data relating to educational or sociodemographic levels, marking a limitation to the study, as higher education or income levels may be associated with greater coffee consumption. But Japan also has a universal health care system, and care is supposedly received regardless of socioeconomic factors.

Because ingredients of Japanese green tea may differ from those in other countries, the authors caution against generalizing findings to other populations.

Reference

Komorita Y, Iwase M, Fujii H, et al. Additive effects of green tea and coffee on all-cause mortality in patients with type 2 diabetes mellitus: the Fukuoka diabetes registry. BMJ Open Diabetes Res Care. Published online October 21, 2020. doi:10.1136/bmjdrc-2020-001252