Worldwide, the number of patients with diabetes is increasing in both developed and developing countries. Diabetic patients are at increased risk for classical micro- and macrovascular diseases as well as nonclassical diseases, such as dementia, malignancy and fragility fracture, which affect both quality of life and life expectancy.
Recent advances in therapeutics (such as sodium-glucose cotransporter 2 inhibitors, glucagon-like peptide-1 receptor agonists, and bariatric surgery) have been remarkable; however, lifestyle improvements are still regarded as the basic therapy.
Asian, especially East Asian, populations have a traditional habit of drinking green tea. Green tea derives from fresh leaves of Camellia sinensis and it contains various chemicals such as phenolic compounds, theanine and caffeine. Through antioxidant, anti-inflammatory, or antibacterial properties, higher green tea consumption has been reported to confer health benefits, including preventing such chronic diseases as diabetes mellitus and reducing mortality.
A study by Yuji Komorita, et al. explored the potential impact of green tea and coffee, separately and combined, on the risk of death among people with diabetes. They tracked the health of 4923 Japanese people (2790 men, 2133 women) with type 2 diabetes (average age 66) for an average of just over 5 years.
They each filled in a 58-item food and drink questionnaire, which included questions on how much green tea and coffee they drank every day. And they provided background information on lifestyle factors, such as regular exercise, smoking, alcohol consumption and nightly hours of sleep. Measurements of height, weight and blood pressure were also taken, as were blood and urine samples to check for potential underlying risk factors.
During the monitoring period, 309 people died. The main causes of death were cancer and cardiovascular disease.
Compared with those who drank neither beverage, those who drank one or both had lower odds of dying from any cause with the lowest odds associated with drinking higher quantities of both green tea and coffee.
Drinking up to 1 cup of green tea every day was associated with 15% lower odds of death; while drinking 2-3 cups was associated with 27% lower odds. Getting through 4 or more daily cups was associated with 40% lower odds.
Among coffee drinkers, up to 1 daily cup was associated with 12% lower odds; while 1 cup a day was associated with 19% lower odds and 2 or more cups was associated with 41% lower odds.
The risk of death was even lower for those who drank both green tea and coffee every day: 51% lower for 2-3 cups of green tea plus 2 or more of coffee; 58% lower for 4 or more cups of green tea plus 1 cup of coffee every day; and 63% lower for a combination of 4 or more cups of green tea and 2 or more cups of coffee every day.
This was an observational study, and as such it can not establish cause. The biology behind these observations isn’t fully understood, explain the researchers. Green tea contains several antioxidant and anti-inflammatory compounds, including phenols and theanine, as well as caffeine. Caffeine is thought to alter insulin production and sensitivity.
Yuji Komorita, 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 Research & Care, 2020; 8
BMJ. “Drinking green tea and coffee daily linked to lower death risk in people with diabetes: 4 or more cups of green tea and 2 or more of coffee linked to 63% lower all cause mortality.” ScienceDaily. ScienceDaily, 20 October 2020.