Habitual coffee consumption and blood pressure: A study of self-defense officials in Japan.

The study aims to examine the relationship between habitual coffee consumption and blood pressure. The subjects were 3336 male self-defense officials aged 48-56 years, who received a preretirement health examination at the Self-Defense Forces Fukuoka Hospital between October 1986 and December 1992. Average coffee intake in the past year was ascertained by a self-administered questionnaire. A significant inverse relation between habitual coffee consumption and blood pressure was found with and without adjustment for alcohol use, cigarette smoking, body mass index, glucose tolerance, and green tea intake. Green tea, another major source of caffeine intake in Japanese, was unrelated to blood pressure. The adjusted mean differences per cup of coffee consumed per day were -0.6 mmHg (95% confident interval [CI]: -0.9 to -0.3, p = 0.0001) in systolic blood pressure and -0.4 mmHg (95% CI: -0.5 to -0.2, p = 0.0002) in diastolic blood pressure. Habitual coffee drinkers had lower blood pressure than non-drinkers at any levels of alcohol use, cigarette smoking, obesity, and glucose intolerance. Our findings consolidate the previous observation that habitual coffee consumption was associated with lower blood pressure.