Key result
Anhydrous caffeine (5 mg/kg) significantly lowered resting heart rate (77.9 vs. 82.5 beats/min) and increased blood pressure and high-frequency HRV power in boys compared to placebo.
Why the study?
Does caffeine alter heart rate variability, heart rate, and blood pressure in 9- to 11-year-old boys?
RCT (n=24)
Double-blind
Random order
Does caffeine alter heart rate variability, heart rate, and blood pressure in 9- to 11-year-old boys?
Absolute Event Rate: 77.9% vs 82.5%
In boys, caffeine increases blood pressure and reflexively decreases heart rate through increased vagal autonomic control.
Caffeine may enhance vagal tone in preadolescent boys; leaves open whether this autonomic shift warrants revised intake guidelines or further mechanistic trials.
It has been consistently reported that blood pressure (BP) is higher and heart rate (HR) is lower in children on caffeine. Studies suggest that the lower HR is a baroreceptor-mediated reflex response to elevated BP caused by caffeine. Purpose: Investigate heart rate variability (HRV) in boys with and without caffeine to investigate if changes in sympathovagal autonomic control support efferent baroreflex impact on HR. Materials and Methods: Twenty-four 9- to 11-year-old boys participated in a double-blind, double-crossover, counterbalanced study. Children received in random order twice each, either a placebo (PL—drink only) or anhydrous caffeine (5 mg/kg) mixed in flavored Sprite®. Following a 60-minute absorption period, supine BP and HR were measured for 5 minutes then 10 minutes of HRV. Results: Resting HR (77.9 ± 7.6 beats·min−1 vs. 82.5 ± 8.6 beats·min−1) was significantly lower, and both systolic (114.1 ± 7.5 mmHg vs. 110.6 ± 7.1 mmHg) and diastolic (64.3 ± 6.2 mmHg vs. 62.2 ± 6.2 mmHg) BP were significantly higher in caffeine versus PL, respectively. High-frequency (HF) power (3359 ± 2632 ms2 vs. 2133 ± 1816 ms2) and HF% (25.7% ± 6.3% vs. 21.1% ± 5.7%) were significantly higher in caffeine versus PL, respectively. Low-frequency percent (23.9% ± 4.8% vs. 27.0% ± 4.4%) was significantly lower on caffeine. In the time domain, root mean square of successive differences (95.1 ± 6.7 ms vs. 72.3 ± 35 ms) and pNN50 (19.6% ± 6.7% vs. 14.4% ± 7.0%) were significantly higher in caffeine versus PL, respectively. Conclusion: In boys, caffeine-induced changes in HRV suggest that the lower HR is due to increased vagal autonomic control. This vagal efferent control of HR is likely the efferent arm of baroreceptors response to the significantly elevated BP with caffeine in the boys.
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Turley et al. (2017) reported an RCT. Anhydrous caffeine vs. Placebo was evaluated on Resting heart rate (beats/min). Anhydrous caffeine (5 mg/kg) significantly lowered resting heart rate (77.9 vs. 82.5 beats/min) and increased blood pressure and high-frequency HRV power in boys compared to placebo.
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