Objectives:
The objective of this systematic review and meta-analysis is to evaluate
the influence of caffeine (CAF) intake strategies, taking into account their form, timing, and dosage,
on heart rate variability (HRV) indices in the post-exercise recovery period.
Methods::
The meta-analysis adhered to the Preferred Reporting Items for Systematic Review
and Meta-Analysis (PRISMA) guidelines and is registered in the PROSPERO database
(CRD42023425885). A comprehensive literature search was carried out across MEDLINE, Web
of Science, LILACS, and SCOPUS, concluding in May 2023. We concentrated on randomized
clinical trials comparing CAF supplementation effects to placebo on HRV indices post-exercise
in active adults aged 18 and above. The primary endpoint was the assessment of HRV indices,
measured both prior to and following exercise.
Results:
Of the 10 studies included, 7 were used for the meta-analysis, and all contributed to the
systematic review. The research explored a variety of CAF strategies, spanning different forms
(capsule, drink, gum), times (10, 45, 60 min) and doses (2.1 to 6.0 mg/kg). The outcomes revealed
no substantial variations between the placebo and CAF conditions in terms of both the
square root of the average of successive squared differences between adjacent RR intervals
(RMSSD) (standardized mean difference (SMD) -0.03, 95% CI -0.265 to 0.197, p=0.77) and
high frequency (HF) index (SMD -0.061, 95% CI -0.272 to 0.150, p=0.57). Furthermore, metaregression
analysis, employing a fixed-effects model and accounting for the administered CAF
doses, revealed no significant correlation between caffeine doses and HRV indices (p>0.05).
Conclusion:
In conclusion, there is moderate-certainty evidence suggesting that different CAF
intake strategies, encompassing aspects such as form, time, and dose, do not have a significant
impact on HRV indices recovery post-exercise (i.e., vagal modulation).