Consuming up to 400mg of caffeine daily, equivalent to as many as five cups of coffee, is safe for most adults and in some cases appears to be linked to a lower risk of cardiovascular disease, according to a new scientific statement by the American Heart Association published in the journal Circulation.
What the statement covers
The statement summarises the most recent evidence on the effects of caffeinated coffee on hypertension, cholesterol, type 2 diabetes, coronary heart disease, stroke, heart failure, atrial fibrillation and other cardiovascular conditions.
Based on the latest research reviewed, consumption of up to 400mg of caffeine per day, corresponding to three to five 240ml cups of plain black coffee without sugars, sweeteners, flavourings or other additives, is considered safe for most adults.
The potential benefits
Drinking coffee without sugar, syrup or cream is associated with a lower risk of developing type 2 diabetes, coronary heart disease, stroke, heart failure and certain heart rhythm disorders. Randomised clinical trials have shown that coffee consumption is linked to a reduced risk of atrial fibrillation, but also to an increased frequency of premature ventricular contractions (PVCs).
Short-term effects and individual differences
Regular coffee consumption can lead some people to develop tolerance to higher caffeine levels, while others experience strong effects even from small amounts. In the short term, caffeine can cause a temporary rise in blood pressure, heart rate, blood sugar and alertness. Some individuals may also experience palpitations or sleep disturbances.
Warning on energy drinks
The statement stresses that higher caffeine intake, such as that found in energy drinks and particularly in concentrated energy shots, may have harmful effects on the heart, including an increased risk of high blood pressure and irregular heart rhythm. Energy drinks, bars and caffeine supplements often contain additional ingredients that enhance caffeine absorption, accelerate its action and may raise the risk of cardiovascular complications.
Why the science is complicated
The authors note that studying the effects of caffeine on the cardiovascular system is difficult. In most research, coffee is the main source of caffeine, and the observed cardiovascular effects may be due to other compounds in coffee. Experimental studies suggest that some of these have antioxidant and anti-inflammatory properties, which may explain part of coffee's beneficial effects.
It is also difficult to separate the effect of caffeine from that of ingredients often added to coffee, such as sugar, syrup, milk or cream. The addition of sugar, flavoured syrups, milk or cream may limit coffee's potential benefits. Moreover, most available studies are observational, meaning they cannot prove cause and effect.
Other sources of caffeine
Beyond coffee, significant sources of caffeine include tea, chocolate, soft drinks, energy drinks and certain over-the-counter or prescription medicines. The evidence to date shows that tea, like coffee, is associated with a lower risk of atrial fibrillation, heart failure and stroke. The scientists stress that more research is needed to assess the effects of different caffeine sources, including soft drinks, energy drinks and dietary supplements.
