Effect of Acute and Chronic Caffeine Use on the Cerebrovascular, Cardiovascular and Hormonal Responses to Orthostasis in Healthy Volunteers

Abstract

1. The effects of acute and chronic caffeine ingestion on supine- and tilt- (60 min at 70 degrees) induced changes in middle cerebral artery velocity (Vmca), heart rate, blood pressure and counter-regulatory hormone levels (catecholamines, growth hormone and cortisol) were studied in nine healthy volunteers. A double-blind, placebo-controlled design was used to study acute effects followed by an open study after 6 days of chronic caffeine use. 2. In the supine position, acute ingestion of caffeine (250 mg) was associated with a fall in Vmca [-11 cm/s, point estimate of difference versus placebo (95% confidence interval: -17, -6) cm/s, P < 0.001] and a rise in mean arterial pressure [+4 (1, 6) mmHg, P < 0.01] and plasma adrenaline levels [+138 (53, 223) pmol/l, P < 0.01]. After chronic caffeine use, the pressor and adrenaline responses, but not the drop in Vmca, were significantly attenuated. 3. On tilting to 70 degrees the fall in Vmca was greater with placebo than after acute caffeine ingestion [-10 (-14, -15) cm/s, P < 0.01], whereas increments (above supine values) in heart rate, mean arterial pressure and hormone levels were unchanged by caffeine. In contrast, the adrenaline [+126 (29, 282) pmol/l, P < 0.01] and noradrenaline [+0.6, 0.9) nmol/l, P < 0.05] responses to tilting were augmented after acute caffeine ingestion. Chronic caffeine supplementation did not alter the fall in Vmca associated with tilting, but significantly attenuated the adrenaline response (P < 0.01 compared with the acute study). 4. Acute caffeine ingestion and orthostasis are both associated with a reduction in Vmca and a rise in mean arterial pressure and adrenaline levels. The acute effects of caffeine on mean arterial pressure and adrenaline but not on Vmca are lost with sustained caffeine intake. These results suggest dissociation between the development of central and peripheral tolerance after chronic caffeine use.

The effect of caffeine, green tea and tyrosine on thermogenesis and energy intake

“…However, the evidence of the effect of caffeine on haemodynamics is inconsistent (Astrup et al, 1991(Astrup et al, , 1992Toubro et al, 1993). Interestingly, the caffeine-induced increase in haemodynamics seems to be diminished by sustained caffeine-intake over time (James, 1994;Debrah et al, 1995). This suggests that subjects may adapt to a high habitual or increased caffeine intake.…”

Influence of Caffeine on Heart Rate Variability in Patients With Long-Standing Type 1 Diabetes

“…The intensity of early warning symptoms of hypoglycemia and early hormonal counterregulatory responses are enhanced by caffeine, allowing individuals to take appropriate action before neuroglycopenia develops (5). Ingestion of modest amounts of caffeine in normal subjects is associated with detectable cardiovascular changes, including a transient increase in blood pressure, although these attenuate with sustained use (6). However, the effects of ingestion of caffeine on autonomic function are unknown.…”

Caffeine Can Decrease Insulin Sensitivity in Humans

“…However, because emergence of tolerance is correlated to individual elimination half-lives of caffeine (40), tolerance may not develop in subjects with short caffeine half-lives. Also, not all caffeine effects appear to be subject to emergence of tolerance (41). Until these issues are resolved, considerations about environmental factors contributing to insulin resistance might include caffeine.…”