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.

A study of caffeine consumption and symptoms; indigestion, palpitations, tremor, headache and insomnia.

In a cross-sectional study of 4558 Australians, it was found that the proportion of subjects reporting indigestion, palpitations, tremor, headache and insomnia increased significantly with mean caffeine intake. A multiple logistic regression model was used to show that the association between the prevalence of these symptoms and usual daily caffeine consumption remained significant in both males and females for palpitations, tremor, headache and insomnia after controlling for the potential confounding factors of age, adiposity, smoking, alcohol intake and occupation. Adiposity was strongly correlated with the prevalence of indigestion and the apparent association between caffeine and indigestion disappeared when adiposity was controlled for. According to the logistic model, the relative risk of experiencing symptoms for people consuming 240 mg of caffeine (approximately 4-5 cups of coffee or tea) per day (the population average) compared with caffeine abstainers is 1.6 for palpitations, 1.3 for tremor, 1.3 for headache, and 1.4 for insomnia in males and 1.7, 1.5, 1.2 and 1.4 respectively for females. Further logistic regression analysis indicated that the associations found between caffeine intake and symptoms did not depend on the source of caffeine. In general, coffee consumption has no significant effect over and above that attributable to its caffeine content. If these associations are causal, then approximately one quarter of the reported prevalence of palpitations, tremor, headache and insomnia is attributable to caffeine consumption in this study population.

Caffeine consumption and serum cholesterol levels.

Caffeine consumption was significantly associated with serum cholesterol levels in women but not in men in a cross-sectional study of 4757 Australians. Use of caffeinated coffee by men, but not total caffeine consumption rate, was significantly associated with raised serum cholesterol. Potential confounding factors including age, adiposity and occupation were controlled for in this analysis. After adjusting for age and adiposity, the mean serum cholesterol level was 11 mg/dl higher for women consuming 200 mg or more of caffeine per day compared with those consuming less. The relative risk of high serum cholesterol (greater than 260 mg/dl) was greater than 2 for women consuming 200 mg or more of caffeine per day. A significant positive interaction between smoking and caffeine consumption in their association with serum cholesterol levels was found for females.

Patterns of caffeine consumption.

A cross sectional survey of 4757 Australians to assess usual daily consumption of caffeine from all sources was conducted. Individual variations in type and strength of coffee drunk were noted. Average caffeine consumption was 240 mg/day, equivalent to approximately five 150 ml cups of medium strength instant coffee. One third of the population had intakes at this level or higher and may be considered to be physically dependent on caffeine. Only 3 per cent of the population were true abstainers from caffeine. Caffeine consumption patterns were similar for men and women of all ages, although younger persons consumed more coffee and less tea than older persons. Tea, coffee and caffeine consumption were all positively associated with tobacco consumption, but only tea consumption was significantly correlated with alcohol intake (negatively).