American Heart Association says up to five cups of coffee a day are safe for most adults

The American Heart Association released a scientific statement concluding that daily caffeine intake of up to 400 milligrams – about five eight-ounce cups of coffee – is safe for the average adult and may even reduce the risk of cardiovascular disease. The review, published in the journal Circulation, examined evidence on stroke, coronary artery disease and arrhythmia, finding a consistent pattern of safety below the 400-mg threshold.

"For the vast majority of individuals that currently enjoy consuming caffeinated coffee or tea, they should be reassured that these substances almost certainly are not increasing their cardiovascular risks and may instead have health benefits," said Gregory Marcus, chief of the volunteer writing group behind the statement and a professor of medicine at the University of California, San Francisco.

The authors noted that moderate coffee consumption can fit within a healthy lifestyle, though they highlighted nuances such as a possible temporary rise in blood pressure with one to three cups and a potential cholesterol-raising effect of cafestol in unfiltered coffee. Benefits appeared strongest for type 2 diabetes, atrial fibrillation, heart attack and stroke, while excessive caffeine could increase premature ventricular contractions, a marker linked to heart-failure risk.

The statement warned that caffeine intake above 400 mg is associated with higher blood pressure and irregular heart rhythms, especially when sourced from energy drinks or shots, which have been less studied and may pose greater health risks.

"Energy drinks have not been as thoroughly studied as caffeine occurring in natural substances (such as coffee or tea), but the available evidence suggests these drinks are more likely harmful than not," Marcus added.