Caffeine produces minor, transitory increases in blood pressure. Habitual users are less prone to exhibit this effect. Its significance is not known (26). Caffeine has also been reported to cause cardiac arrhythmias, but there is conflicting evidence (26). There appears to be a caffeine-intolerant population that is susceptible to this effect. Caffeine may exacerbate an existing tendency toward arrhythmias. Low dosages may decrease heart rate slightly; high dosages may cause tachycardia in sensitive subjects (27). Cerebral blood flow is decreased, and this effect is the basis for its inclusion in drug preparations for the treatment of migraine headaches (28).
Some studies indicate a positive correlation between caffeine intake and the development of hypercholesterolemia, but many very large efforts to confirm this effect, such as the Framingham study, show no correlation between atherosclerotic cardiovascular disease and coffee intake. Other large studies have shown no correlation between coffee drinking and any form of coronary heart disease (27). The disparate results concerning the effects of caffeine on the cardiovascular system probably relate to the size of the studies, lack of control of unrecognized factors and, very importantly, to the acceptance of "cups of coffee" as a quantitative measure of caffeine content. Coffee and tea contain many physiologically active compounds other than caffeine. Coffee oils, especially kahweol, have been shown to be cholesterogenic (29).
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