diabetes: coffee and green tea decrease mortality

 A recent Japanese study found that green tea, coffee, and especially their combination decreased all-cause mortality in patients with diabetes (see dm green tea and coffee dec mortality bmj2020 in dropbox, or doi:10.1136/bmjdrc-2020-001252).

 

Details:

-- 4923 patients with type II diabetes, from the prospective Fukuoka Diabetes Registry (which assesses modern treatments as well as lifestyle in patients with diabetes); this study excluded those with drug-induced diabetes, renal replacement therapy, liver cirrhosis or advanced malignancies, and those with type I diabetes.  99.5% follow-up data

-- mean age 66, about 60% male (fewer males drank at least 4 cups of green tea and more drank at least 2 cups of coffee), BMI 24, current smokers 18% (% decreased with increasing tea consumption, but increased with increasing coffee consumption), alcohol intake 40% (also decreased with more green tea and increased with more coffee consumption), depressive symptoms 9%, mean leisure time physical activity 12 MET-h/wk, sleep duration 7 hours, A1c 7.4%, eGFR 75, LDL 109, HDL 54, blood pressure 130/75 mmHg, history of CVD 23%, insulin therapy 30%, oral agents 63%, antihypertensives 58%, antiplatelet 25%, statins 45%

-- followed prospectively a mean of 5.3 years

-- amounts of green tea and coffee consumed was through self-administered questionnaires

-- 309 patients died during follow-up; main causes of death were cancer (114) and cardiovascular disease (76)

-- primary outcome: all-cause mortality, by an annual assessment through interviews, medical records, letters, telephone calls, etc.

-- results below were adjusted for age, sex, BMI, diabetes duration, current smoking habit, current alcohol intake, leisure time physical activity, sleep duration, A1c, microalbuminuria, LDL, history CVD, and cancer

 

Results:

-- consumption of green tea, multivariate adjusted hazard ratio for all-cause mortality:

    -- up to 1 cup per day: nonsignificant 15% decrease, aHR 0.85 (0.60-1.22)

    -- 2 to 3 cups per day: nonsignificant 27% decrease, aHR 0.73 (0.51-1.03), though very close to significant

    -- at least 4 cups per day: 40% decrease, aHR 0.60 (0.42-0.85)

    -- clinically significant trend with increasing amounts of green tea, p=0.002 for the trend

-- consumption of coffee, for all-cause mortality:

    -- up to 1 cup per day: nonsignificant 12% decrease, aHR 0.88 (0.66-1.18)

    -- 1 cup per day: nonsignificant 19% decrease, aHR 0.81 (0.58-1.13)

    -- at least 2 cups per day, 41% decrease, aHR 0.59 (0.42-0.82)

    -- clinically significant trend with increasing amounts of coffee, p=0.002 for the trend

-- consumption of both (all statistically significant for all-cause mortality):

    -- 2 to 3 cups of green tea plus at least 2 cups of coffee, 51% decrease, aHR 0.49 (0.24-0.99)

    -- at least 4 cups of green tea and 1 cup of coffee: 58% decrease, aHR 0.42 (0.20-0.88)

    -- at least 4 cups of green tea in at least 2 cups of coffee: 63% decrease, aHR 0.37 (0.18-0.77)

-- specific assessment of cancer and cardiovascular mortalities did not show statistically significant associations with either green tea, coffee, or both. However, coffee consumption trended strongly towards benefit from cardiovascular disease mortality, with a weaker trend of benefit from green tea consumption

 

 

 

Commentary:

-- this study occurred in the setting where population intake of green tea is quite high

-- green tea does contain various chemicals that are antioxidant, anti-inflammatory, or antibacterial (eg, phenolic compounds, theanine, and caffeine)

-- coffee, one of the most frequently consumed beverages worldwide, also contains phenolic compounds and (spoiler alert) caffeine, having anti-oxidant, anti-inflammatory and also an anti-mutagenic effect (with evidence of decreased malignancy in some studies). Of note, some studies have found mortality benefit with both caffeinated and decaffeinated coffee. Caffeine also does raise blood pressure, though in this study cardiovascular disease decreased with increased coffee consumption (and, in Japan, the major cardiovascular risk factor historically has been hypertension and not lipids, as in more Western countries)

    -- prior blogs finding coffee consumption associated with decreased mortality: http://gmodestmedblogs.blogspot.com/2017/08/coffee-and-decreased-mortality.html and http://gmodestmedblogs.blogspot.com/2019/01/coffee-and-decreased-mortality.html (which accesses two different blogs)

-- this study adds to the beneficial effects of coffee in the diabetic population, and also adds information about the potential benefit of green tea

-- the prior Ohsaki Study from Japan also found that consuming at least 5 cups green tea per day was associated with a 15% lower risk of all-cause mortality

-- the results on coffee consumption vary a bit in different studies but in general find that, in diabetic patients, coffee is associated with decreased all-cause mortality: 30% in a Finnish study, and in a couple of US Studies, but not the Health Professionals Follow-Up Study. A Dutch study actually found increased mortality in those with a prior MI. The present study in Japan was set in a country with a lower cardiovascular disease risk than in these Western populations

 

Limitations of the study:

-- this was not a randomized controlled trial so we cannot assess causality: did people who drink a lot of green tea and coffee also have other healthful behaviors? For example, there is no further dietary assessment. Did those who drink these beverages also eat a healthier diet, which in and of itself might have had mortality benefit?

    --hard to do a randomized controlled trial over time, with people randomly allotted to groups with prespecified amounts of these liquids to consume.... and for several years.

-- the data on green tea and coffee consumption was assessed using a single, self-reported assessment; this may not necessarily reflect true consumption of these products over the course of the study (eg, any changes in consumption during the study)

-- they did not include medications taken in their analysis, or whether the coffee was caffeinated are not (decaffeinated coffee is uncommonly drunk in Japan) 

-- what about the number of hours of sleep? what % of the coffee drinkers drank coffee to stay awake/function after minimal sleep? what % out of habit (or addiction), or just because they like coffee?

-- and, as a study limited to a single population in Japan, it may not be generalizable to other groups 

 

so, interesting study. It does add to the several studies mentioned above that suggest coffee is in fact healthful. 

Though I might add that sleep deprivation is actually quite deleterious (documented increases in obesity and diabetes, as well as many other afflictions). And, as a means to counteract the short-term effects of sleep deprivation, drinking coffee may in fact be less beneficial (and even serve as an enabler for not sleeping sufficient hours)

geoff

 

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