Green tea, coffee consumption tied to reduced all-cause mortality risk

In patients with type 2 diabetes (T2D), a higher consumption of green tea or coffee was associated with a reduced risk of all-cause mortality, according to the Fukuoka Diabetes Registry study from Japan.

The study population comprised 4,923 adults aged ≥20 years with T2D (mean age 66 years). Frequency of coffee and green tea consumption was identified through self-administered questionnaires. The patients were prospectively followed up for a median 5.3 years, during which time there were 309 deaths, mainly due to cancer (n=114) and cardiovascular disease (CVD; n=76).

Individuals who consumed green tea regularly had a lower risk of all-cause mortality compared with those who did not consume green tea, with the risk reducing with increasing consumption (hazard ratio [HR], 0.85, 95 percent confidence interval [CI], 0.60–1.22 for ≤1 cup/day, HR, 0.73, 95 percent CI, 0.51–1.03 for 2–3 cups/day, and HR, 0.60, 95 percent CI, 0.42–0.85 for ≥4 cups/day; p_trend=0.002). [BMJ Open Diabetes Res Care 2020;8:e001252]

Regular coffee consumption was also tied to a lower risk of all-cause mortality compared with no coffee intake (HR, 0.88, 95 percent CI, 0.66–1.18 for <1 cup/day, HR, 0.81, 95 percent CI, 0.58–1.13 for 1 cup/day, and HR, 0.59, 95 percent CI, 0.42–0.82 for ≥2 cups/day; p_trend=0.002).

All-cause mortality risk was further reduced with the consumption of both coffee and green tea compared with no consumption of both (HR, 0.49, 95 percent CI, 0.24–0.99 for 2–3 cups/day of green tea plus ≥2 cups/day of coffee, HR, 0.42, 95 percent CI, 0.20–0.88 for ≥4 cups/day of green tea plus 1 cup/day of coffee, and HR, 0.37, 95 percent CI, 0.18–0.77 for ≥4 cups/day of green tea plus ≥2 cups/day of coffee).

There was no significant association between amount of green tea or coffee consumed on cancer-related mortality, while the association with CVD-related mortality was marginally insignificant (p_trend=0.08 and 0.06 for amount of green tea and coffee consumed, respectively), said the researchers.

“Higher consumption of green tea and coffee was associated with reduced all-cause mortality. The combined effect of green tea and coffee on mortality appeared to be additive in patients with T2D,” they said.

Previous studies have hinted at a reduced risk of all-cause mortality with green tea consumption in a population that comprised diabetics and non-diabetics. [JAMA 2006;296:1255-1265] However, while coffee consumption has been associated with a reduced mortality risk in the general population, studies on its effect in patients with diabetes have produced conflicting findings. [Diabetologia 2006;49:2618-2626; Diabetes Care 2009;32:1043-1045]

In addition, many of the studies on these associations were conducted in developed nations among populations with higher CVD risk than those in Asia, the researchers said.

While the mechanisms behind the associations are yet to be discerned, bioactive components of the two beverages, such as phenolic compounds and caffeine, may play a role, they said.

“This study suggests that consuming green tea and coffee may have beneficial effects on the longevity of Japanese people with T2D,” they continued. However, the observational study design prevents conclusions on causality. The results may also not be applicable in a non-Japanese population, they said.