It is not uncommon for many people to ask their doctors whether coffee consumption is good for health, especially if they have heart disease or are pregnant. The recent 2015 USA Dietary Group Advisory Committee (DGAC) examined the current evidence on coffee and caffeine consumption.
Generally, while consumption of caffeine-containing beverages, such as coffee and tea are safe, children, pregnant women and women considering conception should avoid consumption of high levels of caffeine such as energy drinks and fortified foods. Generally, there is strong evidence to show that moderate coffee consumption (3 to 5 cups/d or up to 400 mg/d caffeine) is safe and can even be beneficial.
Coffee and Heart Disease
Current evidence suggests that daily consumption of 1 to 4 cups of coffee is associated with decreased total death. The risk reduction associated with each cup of coffee per day was between 3 to 4 percent. Studies on effect of long term consumption of coffee showed that the lowest risk of heart disease was seen with moderate coffee consumption (3 to 5 cups/day), but higher intakes (>5 cups/day) were neither protective nor harmful. Overall, moderate consumption of caffeinated, but not decaffeinated, coffee was associated with a 12 percent lower risk of cardiovascular disease.
Coffee and stroke
The current evidence shows that coffee consumption is associated with an 8 to 13 percent lower risk of stroke however, high consumption of coffee (more than 6 cups daily) was not associated with decreased or increased risk. This beneficial association between coffee consumption and stroke risk was seen mainly for strokes that were due to occlusion of the arteries and not seen in those due to bleeding.
The data of coffee consumption on blood pressure is more mixed. Generally, the data is consistent that low coffee intake has no impact on blood pressure but it may be possible that high coffee consumption may cause an acute increase in blood pressure.
While coffee consumption appeared to contribute significantly to elevation in “bad” or LDL cholesterol, this effect is seen only in unfiltered coffee and not for filtered coffee.
In a meta-analysis of observational study data, including prospective, retrospective, and case-control studies, higher amounts of coffee or caffeine had no association with risk of atrial fibrillation, but low doses of caffeine (<350 mg/day) appeared to have a protective association. In addition, coffee consumption of 1 to 5 cups/day was found to be inversely associated with risk of heart failure in a meta-analysis of five prospective studies. A non-linear association was documented and the lowest risk was observed for 4 cups/day.
Type 2 Diabetes
The current evidence shows that coffee consumption is associated with a reduced risk of type 2 diabetes. Compared to non-drinkers, those drinking 6 to 10 cups of coffee daily had 33 to 37% lower risk for type 2 diabetes. On the average, each cup of coffee was associated with a 6 to 7 percent lower risk of type 2 diabetes.
Coffee and Cancer
Data from 40 prospective cohort studies with an average follow-up of 14.3 years found a 13 percent lower risk of total cancer among coffee drinkers compared to non-drinkers or those with lowest intakes. Coffee intake appears to show a beneficial association with reduced risk of liver cancer, breast cancer, endometrial cancer, oral and pharyngeal cancer.
Coffee and brain
There is consistent evidence to support an association between coffee intake and decreased risk of Parkinson’s disease. There is limited evidence to show that coffee consumption is associated with a modestly lower risk of cognitive decline or impairment and lower risk of Alzheimer’s disease.
Caffeine and Pregnancy Outcomes
Many female coffee lovers who become pregnant are concerned about the effect of continued coffee consumption during pregnancy. The good news that the current observational data consistently shows that moderate caffeine consumption during pregnancy does not increase the risk of preterm birth.
However, high caffeine consumption is associated with a small increased risk of miscarriage, stillbirth, low birth weight, and small for gestational age (SGA) births. Presently, as the data is limited, the DGAC is unable to identify a level of caffeine intake beyond which risk of pregnancy related complications increases. Overall, pregnant women and those planning for conception should exercise restraint in coffee consumption and follow the recommendations of the American Congress of Obstetricians and Gynecologists to not consume more than 200 mg caffeine per day (approximately two cups of coffee per day).
In a recent meta-analysis by Greenwood et al on studies in 60 publications, the data showed that an increment of 100 mg caffeine was associated with a 14 percent increased risk of miscarriage, 19 percent increased risk of stillbirth, 10 percent increased risk of SGA, and 7 percent increased risk of low birth weight. The risk of pre-term delivery was not increased significantly. These associations are more obvious at higher levels of caffeine intake (≥300 mg/day). However, data from many studies did not take into the confounding effects of smoking which was a co-existent habit in many coffee drinkers.
High-dose coffee consumption and health
Evidence on the effects of excessive caffeine intake on the health of adults or children (>400 mg/day for adults; undetermined for children and adolescents) is limited. Some evidence links high caffeine intake in the form of energy drinks to certain adverse outcomes, such as caffeine toxicity and cardiovascular events. Randomized controlled trials (RCTs) on the relationship between high-caffeine energy drinks and cardiovascular risk factors and other health outcomes report mixed results. Evidence also is limited on the health effects of mixing alcohol with energy drinks, but some evidence suggests that energy drinks may mask the effects of alcohol intoxication, so an individual may drink more and increase their risk of alcohol-related adverse events.
Early safety signals consisting of case reports of adverse events associated with high-caffeine drink consumption, including increased emergency room visits, indicate a potential public health problem. The DGAC agrees with the American Academy of Pediatrics and the American Medical Association that until safety has been demonstrated, limited or no consumption of high-caffeine drinks, or other products with high amounts of caffeine, is advised for vulnerable populations, including children and adolescents. High-caffeine energy drinks and alcoholic beverages should not be consumed together, either mixed together or consumed at the same sitting. This is especially true for children and adolescents.
The Food and Drug Administration in the USA defines the upper limit of moderate caffeine intake in healthy adult populations (excluding pregnant women) as 400 mg/day, beyond which consumption is considered excessive. For children and adolescents, the current guideline based on Health Canada recommendations, defines the upper limit as not more than 2.5 mg of caffeine per kg bodyweight per day.
While coffee, tea and soft drinks have been the main sources of caffeine, caffeine containing energy drinks are presently becoming a source of concern. The Institute of Medicine under the auspices of the FDA conducted a workshop on caffeine intake and concluded that children and adolescents are a potential vulnerable group, in whom caffeine intake could have detrimental health consequences. In 2010, the FDA determined that caffeine added to alcoholic beverages was not generally recognized as safe (GRAS), leading to withdrawal of premixed, caffeinated alcoholic beverages from the market. Currently, Health Canada limits caffeine levels for energy drinks at 100 mg/250 ml (~1 cup) and have mandated that the energy drinks carry a warning label stating that energy drinks should not be combined with alcohol.
In 2014, the Centre for Disease Control in the USA has publicly stated that high caffeine content in energy drinks can mask the intoxicating effects of alcohol, without any effect on the metabolism of alcohol by the liver. Hence, the high caffeine may result in an “awake” state of intoxication, thus increasing the risk of alcohol-related harm and injury.