Caffeine consumption and blood pressure: an epidemiological study.

A cross-sectional survey of 5147 Australians attending a health screening clinic was conducted to determine if there was an association between habitual consumption of caffeine, or particular caffeine-containing beverages, and blood pressure. The average caffeine consumption of the study population was 240 mg/day. Caffeine consumption within the last three hours was found to be associated with significantly higher mean systolic and diastolic blood pressure in both sexes after controlling for age, adiposity, first degree relatives with hypertension, serum cholesterol level, alcohol consumption and tobacco smoking. Mean systolic and diastolic blood pressures differed significantly by 4 mmHg and 2 mmHg respectively for both males and females between those who had consumed caffeine within the last three hours and those who had not consumed it within the last nine hours (p less than 0.01). Average caffeine consumption per day was not associated with blood pressure in either sex after controlling for time since caffeine consumption. Logistic regression analysis was used to estimate the relative risk of high blood pressure (treated and untreated) for the groups consuming and not consuming caffeine in the last three hours. This relative risk was significantly greater than unity in females only (p less than 0.05). After controlling for time since caffeine consumption, caffeine consumption per day was not associated with significantly increased risk of high blood pressure.