Science - April 21, 2005

Coffee has little effect on blood pressure

Coffee drinkers who are worried about their heart and arteries can breathe a sigh of relief. The blood pressure raising effect of coffee is nil, according to an article by Wageningen researchers in the Journal of Hypertension.

The Wageningen researchers gathered sixteen reliable experiments on the effects of coffee on humans, brought all the results together and analysed them again. Researchers had given their subjects coffee or caffeine, the stimulant in coffee. A cup of weak coffee contains anywhere between 10 and 30 milligrams of caffeine, but strong coffee can contain more than 100 milligrams.

With a consumption of three quarters of a litre of coffee per day the systolic blood pressure, the pressure during the heartbeat, rose by 1.2 millimetres of mercury pressure. The rise in the diastolic blood pressure, the pressure between two heartbeats, was 0.5 millimetres of mercury pressure. The researchers refer to this as a ‘small effect’.

Caffeine given in pure form had a larger effect. A daily dose of 410 milligrams, an amount you could theoretically consume if you drink three quarters of a litre of coffee a day, led to an increase of 4.2 millimetres mercury pressure in the systolic pressure and 2.4 millimetres in the diastolic pressure.

It is possible that coffee contains substances that weaken the effect of caffeine. ‘These could be polyphenols, potassium or magnesium,’ says project supervisor Dr Marianne Geleinse. ‘But maybe it’s because drinking a cup of coffee also makes you relax. If you take caffeine pills you don’t get the relaxation.’ The researchers also examined the effect of coffee on the heart rate. This was negligible. / WK