There’s good news for lovers of coffee: not only does coffee drinking not increase the risk of heart disease, but consuming 3 to 5 cups daily may actually reduce the risk of gallstones, keep the liver healthy, and slightly reduce the risk of obesity.
Those glad tidings emerged from a special report by a trio of Harvard heavy hitters, Rob M. van Dam, PhD, Frank B. Hu, MD, PhD, and Walter C. Willett, MD, DrPH, who authored a special report on “Coffee, Caffeine, and Health” published in The New England Journal of Medicine.
They pointed out that concerns about the health effects of coffee, and other sources of caffeine like tea or energy drinks, are not new, but of late the conversation has turned to evidence of health benefits.
“A key issue in research on caffeine and coffee is that coffee contains hundreds of other biologically active phytochemicals, including polyphenols such as chlorogenic acid and lignans, the alkaloid trigonelline, melanoidins formed during roasting, and modest amounts of magnesium, potassium, and vitamin B3 (niacin). These coffee compounds may reduce oxidative stress, improve the gut microbiome, and modulate glucose and fat metabolism. In contrast, the diterpene cafestol, which is present in unfiltered coffee, increases serum cholesterol levels. Thus, research findings for coffee and other dietary sources of caffeine should be interpreted cautiously, since effects may not be due to caffeine itself,” they wrote.
The body absorbs caffeine pretty quickly — from 45 minutes to 2 hours — and it not only circulates in the blood but also crosses the blood-brain barrier and gets into the liver. Among adults, the half-life of caffeine “is typically 2.5 to 4.5 hours,” but in babies the half-life can be as long as 80 hours. Smoking greatly reduces the half-life of caffeine, which may explain increased coffee consumption by smokers. Pregnancy, on the other hand, can extend the half-life of caffeine, “especially in the third trimester, when the half-life of caffeine can be up to 15 hours.”
van Dam et al broke down the effects of caffeine on symptoms as well as disease. Among their findings:
- Cognition and pain: Caffeine blocks adenosine in the brain and the result is a boost in cognition, less sleepiness, and improved “vigilance during tasks of long duration that provide limited stimulation, such as working on an assembly line, long-distance driving, and flying an aircraft.” Combining caffeine with an analgesic will boost pain relief, a finding confirmed in 19 studies.
- Sleep, anxiety, hydration and withdrawal symptoms: Caffeine can interfere with sleep, especially caffeine consumed late in the day and among caffeine sensitive persons, and for those with bi-polar disorder, high caffeine consumption can increase anxiety (>200 mg per occasion or >400 mg day). Caffeine stimulates urine output, but moderate doses (400 mg or less daily) have not been linked to dehydration. Caffeine withdrawal does occur, and symptoms can include headaches, fatigue, decreased alertness, or depression but symptoms usually last only 2-9 days.
- Toxic effects: At very high doses—1.2 g or more—caffeine can produce a number of symptoms including anxiety, dyphoria, insomnia, and psychomotor agitation. “A recent review of blood caffeine levels in cases of fatal overdoses showed that the median postmortem blood caffeine level was 180 mg per liter, which corresponds to an estimated intake of 8.8 g of caffeine,” they wrote. “Caffeine poisoning from consumption of traditional sources of caffeine such as coffee and tea is rare because a very large amount (75 to 100 standard cups of coffee) would have to be consumed in a short time for the dose to be fatal. Caffeine-related deaths have generally been due to very high doses of caffeine from tablets or supplements in powdered or liquid form, mostly in athletes or patients with psychiatric disorders.” High energy drinks mixed with alcohol have “been linked to adverse cardiovascular, psychological and neurologic events.”
- Blood pressure, lipids and CVD: Initial exposure to caffeine “raises epinephrine levels and blood pressure in the short term. …However, no substantial effect on blood pressure was found in trials of caffeinated coffee,” they wrote. Consuming 6 or more cups daily of unfiltered coffee — French press, Turkish, or Scandinavian boiled coffee—has been shown to increase LDL and is associated a higher risk of cardiovascular events, but filtered coffee, which is the standard coffee in the U.S., does not increase LDL. “Findings consistently indicate that consumption of up to 6 standard cups of filtered, caffeinated coffee per day, as compared with no coffee consumption, is not associated with an increased risk of these cardiovascular outcomes in the general population or among persons with a history of hypertension, diabetes, or cardiovascular diseases. In fact, coffee consumption was associated with a reduced risk of cardiovascular diseases, with the lowest risk for 3 to 5 cups per day. An inverse association has been observed between coffee consumption and coronary artery disease, stroke, and death from cardiovascular causes.”
- Weight and type 2 diabetes: A number of studies have suggested that black coffee may provide a modest benefit in weight control, and caffeine intake reduces short term insulin sensitivity. “This may reflect an inhibitory effect of caffeine on storage of glucose as glycogen in muscle and may partly result from increased epinephrine release. However, consumption of caffeinated coffee (4 to 5 cups per day) for up to 6 months does not affect insulin resistance,” they noted. “In addition, consumption of both caffeinated and decaffeinated coffee reduces hepatic insulin resistance induced by fructose overfeeding. Furthermore, in cohort studies, habitual coffee consumption has been consistently associated with a reduced risk of type 2 diabetes in a dose-response relationship, with similar associations for caffeinated and decaffeinated coffee. Taken together, these findings suggest that tolerance develops for the adverse effect of caffeine on insulin sensitivity or that the adverse effect is offset by longer-term beneficial effects of noncaffeine coffee components on glucose metabolism, possibly in the liver.
- Cancer and coffee: Multiple prospective cohort studies debunk supposed links between coffee/caffeine consumption and cancer. “Coffee consumption is associated with a slightly reduced risk of melanoma, nonmelanoma skin cancer, breast cancer, and prostate cancer. Stronger inverse associations have been observed between coffee consumption and the risk of endometrial cancer and hepatocellular carcinoma. For endometrial cancer, the associations are similar with caffeinated and decaffeinated coffee, whereas for hepatocellular carcinoma, the association appears to be stronger with caffeinated coffee,” they wrote. Coffee has also been shown to reduce liver enzymes, and lower risk of fibrosis and cirrhosis. Coffee has also been associated with reduced risk of gallstones.
- Neurologic diseases: Seven prospective cohort studies have found that consuming 3 or fewer cups of caffeinated coffee is associated with a 31% lower relative risk of Parkinson’s disease (95% CI 0.61-0.77) P <0.01) but the lower risk levels off at >3 cuts/day. “Coffee and caffeine consumption have also been associated with reduced risks of depression and suicide in several cohorts in the United States and Europe, although these findings may not hold in persons who have very high intakes (≥8 cups per day). Coffee consumption has not been consistently associated with the risk of dementia or Alzheimer’s disease.”
Coffee consumption in pregnancy is another issue. Caffeine does pass the placenta, and high caffeine consumption during pregnancy is associated with low-birth weight babies. “Caffeine may induce uteroplacental vasoconstriction and hypoxia by increasing blood catecholamine levels in the mother and fetus. Associations with low birth weight have been observed for both coffee and tea (in a predominantly tea-drinking population) and showed a dose–response relationship, without a clear threshold. In contrast, the association between caffeine and pregnancy loss was not significant at lower levels of intake and may have been affected by publication bias.” All of this adds up to some simple conclusions: Drinking 3 to 5 cups of coffee daily is likely to reduce the risk of a number of chronic diseases and won’t cause heart attacks. The authors suggested “limits of 400 mg of caffeine a day for adults who are not pregnant or lactating and 200 mg for pregnant and lactating women…”
Be aware that this special report finds that coffee or caffeine can be part of a healthy diet.
Caffeine consumption should be limited to 400 mg daily (3-5 cups of coffee) for adults and 200 mg for pregnant or lactating women.
Peggy Peck, Editor-in-Chief, BreakingMED™
Hu reported receiving honoraria from Standard Process and consulting fees from Diet Quality Photo Navigation. No other potential conflict of interest relevant to this article was reported.
Cat ID: 925
Topic ID: 915,925,730,5,6,188,191,41,192,94,925