Coffee, tea and energy drinks

The NIH-AARP Diet and Health Study assessed coffee intake once in 229,119 men and 173,141 women aged 50 to 71, excluding those with cancer, heart disease or stroke, and followed them from 1995 to 2008, during which 52,515 died. Before adjustment, coffee drinkers had higher mortality, largely because they were more likely to smoke. After adjustment for smoking and other factors, coffee was inversely associated with mortality in a graded way. Compared with non-drinkers, hazard ratios (the risk in one group relative to another; 0.88 means 12% lower) among men were 0.94 for one cup a day, 0.90 for two or three, 0.88 for four or five and 0.90 for six or more; among women they were 0.95, 0.87, 0.84 and 0.85. Coffee was associated with fewer deaths from heart disease, respiratory disease, stroke, injuries and accidents, diabetes and infections, but not from cancer, and results were similar in people who had never smoked [1].

The European Prospective Investigation into Cancer and Nutrition (EPIC) followed 521,330 people in 10 countries for a mean of 16.4 years, with 41,693 deaths. The highest quarter of coffee consumers had lower all-cause mortality than non-consumers (hazard ratio 0.88 in men and 0.93 in women) and much lower mortality from digestive diseases (0.41 in men and 0.60 in women), but women in the highest quarter had higher ovarian cancer mortality (hazard ratio 1.31) [9]. An umbrella review of 201 meta-analyses of observational research and 17 of interventional research found coffee more often associated with benefit than harm. The largest risk reductions were at three to four cups a day, with relative risks of 0.83 for all-cause mortality, 0.81 for cardiovascular mortality and 0.85 for cardiovascular disease, and high compared with low consumption was associated with 18% lower cancer incidence. Harmful associations largely disappeared after adjustment for smoking, with two exceptions: in pregnancy, high intake was associated with low birth weight, preterm birth and pregnancy loss, and in women, coffee drinking was associated with higher fracture risk [2].

A UK Biobank study of 171,616 adults without cardiovascular disease or cancer, followed for a median of 7.0 years, separated coffee by sweetening. The association with mortality was U-shaped for unsweetened, sugar-sweetened and artificially sweetened coffee. Compared with non-drinkers, drinkers of unsweetened coffee had 16 to 29% lower all-cause mortality across all intake levels. For sugar-sweetened coffee, mortality was 31% and 28% lower at more than 1.5 to 2.5 and more than 2.5 to 3.5 drinks a day, while the lowest and highest intakes showed no significant difference. Results for artificially sweetened coffee were less consistent. U-shaped associations were also found for instant, ground and decaffeinated coffee [10], which suggests that compounds other than caffeine contribute to the association.

Heavily sweetened coffee drinks overlap with sugar-sweetened beverages, which in 118,363 US adults were associated with 21% higher total mortality at two or more servings a day compared with less than one a month [11].

In the Ohsaki study, 40,530 Japanese adults aged 40 to 79 were followed for up to 11 years for all-cause mortality. Green tea was associated with lower all-cause and cardiovascular mortality, more strongly in women. Compared with less than one cup a day, five or more cups was associated with hazard ratios for all-cause mortality of 0.88 in men and 0.77 in women, and for cardiovascular mortality in women the hazard ratio was 0.69 [3].

In the UK Biobank, where black tea is the main type consumed, 498,043 adults aged 40 to 69 were followed for a median of 11.2 years. Compared with no tea, hazard ratios for all-cause mortality were 0.95 for one cup or less a day, 0.87 for two to three cups, 0.88 for four to five and six to seven cups, 0.91 for eight to nine and 0.89 for ten or more. Tea was also associated with lower mortality from cardiovascular disease, ischaemic heart disease and stroke, and the findings were similar whether or not participants drank coffee and regardless of genetic differences in caffeine metabolism. Portion size and tea strength were not assessed [4]. In a small acute experiment in 16 women, black tea improved flow-mediated dilation (a measure of blood vessel function) two hours after drinking compared with water, and adding milk abolished this effect, which the authors attributed to milk caseins binding tea catechins [12].

Energy drinks combine caffeine with sugar or sweeteners and other ingredients, and unlike coffee and tea they have been studied mainly in short-term trials. In a randomised, double-blind, placebo-controlled crossover trial (in which each participant receives every drink in random order), 34 healthy volunteers aged about 22 drank 32 ounces of one of two energy drinks or a placebo within an hour on separate days. The maximum rise in the corrected QT interval (a measure of the time the heart's ventricles take to recharge between beats; prolongation can predispose to dangerous rhythms) was 17.9 and 19.6 milliseconds with the energy drinks and 11.9 milliseconds with placebo, and peripheral and central blood pressures were significantly higher with the energy drinks [5].

A smaller crossover trial in 8 young men compared 355 mL of Red Bull, sugar-free Red Bull, water with 120 mg of caffeine, and water with placebo. All three active drinks raised blood pressure by a similar 3 to 4 mmHg compared with placebo, but by different routes: the sugared drink raised heart rate, stroke volume, cardiac output and contractility, while the sugar-free drink and plain caffeine raised peripheral vascular resistance. The other ingredients (taurine, glucuronolactone and B vitamins) did not appear to influence these pathways [13]. None of these trials measured long-term outcomes, and no studies comparable in size to those of coffee and tea have followed energy drink consumers for mortality.

In a placebo-controlled study of 12 healthy normal sleepers, 400 mg of caffeine taken at bedtime, 3 hours before or 6 hours before bedtime each significantly disturbed sleep measured at home, and even at 6 hours caffeine reduced total sleep by more than 1 hour [6]. A 2023 meta-analysis (a study that pools the results of earlier studies) of 24 studies found that caffeine reduced total sleep time by 45 minutes and sleep efficiency by 7%, lengthened the time taken to fall asleep by 9 minutes and increased time awake after falling asleep by 12 minutes, while deep sleep fell by 11.4 minutes. The authors estimated that a typical cup of coffee (107 mg per 250 mL) needs to be drunk at least 8.8 hours before bedtime to avoid reducing total sleep time [7]. Caffeine as a cause of poor sleep is described under insomnia.

A systematic review of 381 studies published between 2001 and 2015 assessed caffeine's potential adverse effects against intake levels set by Health Canada. It concluded that up to 400 mg a day in healthy adults is not associated with overt adverse cardiovascular, behavioural, reproductive, developmental, acute or bone effects, and that up to 300 mg a day in healthy pregnant women is generally not associated with adverse reproductive or developmental effects [8]. The American College of Obstetricians and Gynecologists concluded that moderate intake of less than 200 mg a day does not appear to be a major factor in miscarriage or preterm birth [14]. In observational data, high coffee intake in pregnancy was associated with low birth weight, preterm birth and pregnancy loss [2]. Coffee and tea also contribute to daily fluid intake, as described under hydration.

Full deep dive: Coffee, tea and energy drinks.