Hypertension is a known risk factor for cardiovascular and kidney disease and also increases all cause mortality. Many lifestyle factors have been identified that are known to affect blood pressure, including stress, smoking and exercise. The link between coffee consumption and hypertension is controversial despite the issue being researched for more than 75 years. The mechanism by which coffee can increase blood pressure is though to relate to activation of the central nervous system which results in increased circulating levels of the catecholamine hormones, adrenaline and noradrenaline. The physiological changes brought about by this sympathetic activation include increased heart rate and vasoconstriction, the combination of which results in higher blood pressure. However, the controversy surrounding coffee exists because regular coffee consumption results in down-regulation of the sympathetic response, such that habitual coffee drinkers may not experience large increases in circulating catecholamines.
Meta-analyses of randomised clinical trials have previously found that coffee intake can cause a slight increase in blood pressure. However, these studies involved short term trials that did not take into account that habitual consumption down-regulates the physiological effects. This may result in an overestimation of the effects of coffee on blood pressure. Therefore, researchers1 have performed a meta-analysis including long-term prospective studies investigating the association between coffee consumption and blood pressure. The analysis involved 172 567 subjects and 31 135 reported cases of hypertension with a mean follow up period of 6.4 to 33.0 years. The results showed that when dose-response was considered, a ‘J’-shaped curve resulted, such that at low coffee consumption of less that 3 cups per day hypertension risk increased, but over this amount higher intakes of coffee resulted in a gradual levelling out of the risk.
These results suggest that high intakes of coffee do not result in a substantially increased risk of hypertension compared with drinking ≈3 cups/d. The lowest intake of coffee was reported as about 237mL/day which was 1 cup, and from this value the pooled relative risks for subsequent higher intakes were 1.09 (up to 3 cups/d), 1.07 (3 to 5 cups/d) and 1.08 (>5 cups/d). These are very small changes to the relative risk and this supports previous studies that shows that coffee consumption causes only very small increases in the risk of hypertension. The authors estimated that there was a 9% increase in hypertension associated with light-to-moderate consumption. The most plausible reason for the ‘J’-shaped curve is the down-regulation to the sympathetic nervous system. In addition, coffee contains other substances such as flavonoids, chlorogenic acid, melanoids, quinide, magnesium, cafestol and kahweol that may have beneficial effects on blood pressure.
RdB
