Summary and Concluding Remarks:
There is little evidence of health risks and considerable evidence of long-term health benefits for adults consuming moderate amounts of coffee (3–4 cups/day).
However, mechanisms underlying the beneficial actions of coffee against cardiovascular and liver disease and glucose metabolism are not yet fully understood. The data documenting the health benefits of coffee are based on observational studies mainly, and are currently insufficient to recommend increased coffee consumption as an intervention strategy for risk reduction in type 2 diabetes and other metabolic diseases.
A growing body of epidemiological research data suggests that coffee consumption may help prevent several chronic diseases, including type 2 diabetes, Parkinson's disease and liver disease. ... 23 Aug 2013
A meta-analysis covering 457,922 individuals and 18 studies concluded that an inverse log-linear relationship exists between coffee consumption and subsequent risk of diabetes: each additional cup of coffee consumed per day is associated with a 7 % reduction in the excess risk of diabetes (relative risk [RR] 0.93 95 % confidence interval [CI] 0.91–0.95) after adjustment for potential confounders.
Individuals consuming 3 to 4 cups of tea daily have a 28 % lower risk of type 2 diabetes.
A systematic review of cohort studies (from January 2001 to August 2011) confirmed the association between coffee consumption and reduced risk of type 2 diabetes, and also found an advantage of filtered Coffee over pot Coffee .......
The inverse relationship between coffee consumption and type 2 diabetes remains when lifestyle factors are taken into account: analysis of a Finnish cohort study found that the risk of type 2 diabetes was reduced by half in obese and inactive individuals who consumed ≥7 cups of coffee daily compared with those who consumed <2 cups/day...
A meta-analysis of 10 published studies found a significant inverse association between coffee drinking and hepatocellular carcinoma. A recent meta-analysis of nine published case-control and seven cohort studies has also found a significant inverse association between coffee consumption and all liver cancers. A dose response seems to exist, and a significant protective effect of coffee may start from 3 cups of coffee per day. Coffee drinking has also been associated with reduced risk of alcoholic cirrhosis and hepatic fibrosis in patients with chronic liver diseases, such as hepatitis C, fatty liver disease and non-alcoholic steatohepatitis.
The Effects of Coffee Consumption on Neurodegenerative Diseases
Numerous epidemiological studies have reported an inverse association between coffee consumption and the risk of developing Parkinson’s disease. A systematic review and meta-analysis of published studies examining the relation between caffeine intake and cognitive decline or dementia found a trend towards a protective effect of caffeine, although considerable heterogeneity was found across the methodology employed, and the number of epidemiological studies was limited. The authors concluded that no definite link between coffee consumption and dementia could be established. A Finnish study found coffee drinkers at midlife had lower risk of dementia and Alzheimer’s disease later in life compared with those drinking no or only little coffee, and that the lowest risk of dementia was found in people who drank 3 to 5 cups per day. Several other studies have suggested that moderate caffeine intake (corresponding to 5 cups of coffee per day) may protect against or treat Alzheimer’s disease.
A meta-analysis of 21 prospective cohort studies found no association between coffee consumption and CHD. In fact, moderate coffee consumption was associated with a significantly reduced risk of CHD. A European prospective study analysed data from 42,659 participants in the European Prospective Investigation into cancer and Nutrition (EPic)-Germany study. coffee consumption was not associated with increased incidence of CVD. A Japanese cohort study (n=76,979) found that consumption of coffee was associated with a reduced risk of cVD mortality. The US Nurses’ Health Study (n=83,076) found that long-term coffee consumption was associated with a modest reduction in the risk of stroke. Intake of coffee has been associated with an increased risk of nonfatal myocardial infarction (MI) among individuals with the CYP1A2 genotype, indicating slow caffeine metabolism.
Coffee has been implicated as a risk factor for hypertension but a prospective cohort study from the Nurses’ Health Studies I and II (n=155,594) found no association between caffeine intake and the risk of hypertension. A recent systematic review and meta-analysis of 15 studies did not show any statistically significant effect of coffee consumption on blood pressure (BP) or the risk of hypertension. However, the studies were of low quality and the authors concluded that no recommendation can be made for or against coffee consumption in relation to these indications.
BMJ 2017; 359 doi: https://doi.org/10.1136/bmj.j5024 (Published 22 November 2017)Cite this as: BMJ 2017;359:j5024
There was evidence of a non-linear association between consumption and some outcomes, with summary estimates indicating largest relative risk reduction at intakes of three to four cups a day versus none, including all cause mortality (relative risk 0.83, 95% confidence interval 0.83 to 0.88), cardiovascular mortality (0.81, 0.72 to 0.90), and cardiovascular disease (0.85, 0.80 to 0.90). High versus low consumption was associated with an 18% lower risk of incident cancer (0.82, 0.74 to 0.89). Consumption was also associated with a lower risk of several specific cancers and neurological, metabolic, and liver conditions. Harmful associations were largely nullified by adequate adjustment for smoking, except in pregnancy, where high versus low/no consumption was associated with low birth weight (odds ratio 1.31, 95% confidence interval 1.03 to 1.67), preterm birth in the first (1.22, 1.00 to 1.49) and second (1.12, 1.02 to 1.22) trimester, and pregnancy loss (1.46, 1.06 to 1.99).
Coffee consumption seems generally safe within usual levels of intake, with summary estimates indicating largest risk reduction for various health outcomes at three to four cups a day, and more likely to benefit health than harm. Robust randomised controlled trials are needed to understand whether the observed associations are causal. Importantly, outside of pregnancy, existing evidence suggests that coffee could be tested as an intervention without significant risk of causing harm. Women at increased risk of fracture should possibly be excluded.
BMJ 2017; 359 doi: https://doi.org/10.1136/bmj.j5381 (Published 22 November 2017)
Drinking three to four cups of coffee a day is associated with health benefits across a range of diseases and conditions. A review published in The BMJ this week identified 201 meta-analyses of observational research and 17 meta-analyses of interventional research and found that coffee consumption was more often associated with benefit than harm over various health outcomes.1
The researchers found that drinking three cups of coffee a day was associated with the greatest benefit in terms of cardiovascular disease, coronary heart disease, and stroke, when compared with not drinking coffee. Consumption at this level was associated with a 19% lower risk of mortality from cardiovascular disease (relative risk 0.81, 95% confidence interval 0.72 to 0.90), a 16% lower risk of mortality from coronary heart disease (relative risk 0.84, 0.71 to 0.99), and a 30% lower risk of stroke mortality (0.70, 0.80 to 0.90).