Drinking green tea, coffee linked to lower mortality in diabetes patients

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Drinking both green tea and coffee was linked to a lower risk of all cause mortality among people with type 2 diabetes, according to a new observational study published in the journal BMJ Open Diabetes Research & Care.

In the study, drinking four or more daily cups of green tea plus two or more of coffee was associated with a 63 percent lower risk of death over a period of around five years. The researchers tracked the health of 4,923 Japanese people, 2,790 men and 2,133 women, with type 2 diabetes and an average age 66 years old for an average of just over five years.

Study participants were enrolled in The Fukuoka Diabetes Registry, a multicenter prospective study looking at the effect of drug treatments and lifestyle on the lifespan of patients with type 2 diabetes. The individuals each filled in a 58-item food and drink questionnaire, which included questions on how much green tea and coffee they drank every day. Additionally, 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.

Some 607 of the participants didn't drink green tea, while 1,143 drank up to a cup a day, 1,384 drank two to three cups, and 1,784 drank four or more. In addition, 994 of the participants didn't drink coffee, while 1,306 drank up to one cup daily, 963 drank a cup every day, and 1,660 drank two or more cups.

During the monitoring period, 309 people died. The main causes of death were cancer and cardiovascular disease, according to the study.

Compared with those who drank neither beverage, the researchers found that 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.

Specifically, drinking up to one cup of green tea every day was associated with 15 percent lower odds of death, while drinking two to three cups was associated with 27 percent lower odds. Four or more daily cups was associated with 40 percent lower odds. Among coffee drinkers, up to one daily cup was associated with 12 percent lower odds, while one cup a day was associated with 19 percent lower odds. Two or more cups was associated with 41 percent lower odds, the study found.

The risk of death was lower for those who drank both green tea and coffee every day, 51 percent lower for two to three cups of green tea plus two or more of coffee, 58 percent lower for four or more cups of green tea plus one cup of coffee every day, and 63 percent lower for a combination of four or more cups of green tea and two or more cups of coffee every day.

This is an observational study, and as such, can't establish cause. The researcher said there are also several caveats, including the reliance on subjective assessments of the quantities of green tea and coffee drunk.

The biology behind these observations isn't fully understood, the researchers said. Green tea contains several antioxidant and anti-inflammatory compounds, including phenols and theanine, as well as caffeine. Coffee also contains numerous bioactive components, including phenols. Beyond its potentially harmful effects on the circulatory system, caffeine is thought to alter insulin production and sensitivity.

“This prospective cohort study demonstrated that greater consumption of green tea and coffee was significantly associated with reduced all-cause mortality,” the researchers said in a statement. “The effects may be additive.”