Two Cups of Coffee a Day Linked to Lower Heart Risk and Longer Life, Large UK Study Finds

Researchers who followed more than 400,000 Britons for at least a decade have concluded that a daily coffee habit, long eyed warily by some doctors, does not appear to harm the heart and may protect it. The findings were presented at an American College of Cardiology meeting in Washington DC.

The team drew on the UK Biobank, examining coffee consumption that ranged from up to one cup a day to more than six. They compared those levels against heart rhythm problems, cardiovascular disease, and deaths from all causes and from heart-related causes.

The analysis covered 382,535 men and women with an average age of 57 who had no known heart disease at the start. A second group of 34,279 people already had some form of cardiovascular illness. Within that group, 24,111 had an arrhythmia, an irregular heartbeat, when the study began.

The best results appeared at two to three cups a day. Compared with people who never drink coffee, those drinkers had a 10 to 15 per cent lower risk of developing coronary heart disease, heart failure or a heart rhythm problem, or of dying for any reason. Among people who already had cardiovascular disease, two to three cups was also linked with lower odds of death. Those who drank less than two cups or more than three did less well overall, though the risk of stroke or heart-related death was lowest among people drinking one cup a day.

For people with arrhythmias, drinking coffee was associated with a lower risk of death. Those with atrial fibrillation, in which the heart beats rapidly, were nearly 20 per cent less likely to die if they drank one cup a day than were non-drinkers. Coffee at any amount did not raise the risk of rhythm problems, including AFib or atrial flutter, which is often what clinicians worry about. In many cases the benefits held regardless of exercise, alcohol, smoking, diabetes and high blood pressure.

Senior author Professor Peter Kistler of the Baker Heart Institute in Melbourne, Australia, said coffee can quicken the heart rate, which is why some people fear it could trigger or worsen heart problems, and why general advice to give it up may exist. He said clinicians often err on the side of caution with patients who have known cardiovascular disease or arrhythmias. His team's data, he said, suggest coffee should not be discouraged but included as part of a healthy diet for people with and without heart disease. He described the effect as either neutral or associated with benefit.

Kistler pointed to a range of possible mechanisms. Coffee beans contain over 100 biologically active plant chemicals, which dampen oxidative stress and inflammation and improve insulin sensitivity and metabolism. They also block absorption of fat into the gut, and of molecules linked to abnormal heart rhythms.

The researchers also looked at instant, ground, caffeinated and decaffeinated coffee. Two to three cups a day was again best, and lower death rates appeared across all types. Decaf did not show favourable effects against arrhythmia, though it was linked to reduced cardiovascular disease, except heart failure. Kistler said this suggests caffeinated coffee is preferable and that decaf offers no advantage.

Cardiovascular disease is the world's leading killer, claiming an estimated 17.9 million lives a year. Coffee has also been linked with lower rates of cancer, dementia, diabetes and depression. People are usually advised to stay under four cups a day, about 400mg of caffeine, since it is a stimulant that can cause insomnia and muscle tremors. Because the study tracked existing habits rather than assigning coffee to participants, it shows association, not proof of cause, and guidance for patients may shift only as further evidence arrives.