This research is aimed to systematically review heart rate variability (HRV) findings of functional somatic syndromes (FSSs) and somatic symptom disorders (SSDs), and to compare the HRV values between FSSs/SSDs patients and healthy individuals. We included clinical studies assessing HRV (including baseline HRV and HRV reactivity) in FSSs/SSDs and healthy participants. We searched PubMed, Embase, PsycINFO, MEDLINE, and Web of Science databases from the earliest available date to June 2019. Eighty-five studies comprising 3242 FSSs/SSDs patients and 2321 controls were included in the main meta-analysis; the baseline HRV value was significantly lower compared to healthy individuals (Hedges'g, -0.43; 95 % CI, -0.54 to -0.30; p < .001), with the largest effect size in fibromyalgia patients. A significant lower HRV was also found for total variability (Hedges'g, -0.56; 95 % CI, -0.77 to -0.36) and specific parasympathetic indices (Hedges'g, -0.41, 95 % CI; -0.54 to -0.30). HRV reactivity was significantly lower in FSSs/SSDs patients (Hedges'g, -0.42; 95 % CI, -0.64 to -0.20). Our results support the notion that FSSs/SSDs patients have significantly lower HRV than healthy individuals.
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