Table 2. Non-genetic potential confounding factors associated with HRV indices among participants stratified by PSS score.

	LF		HF		LF/ HF		RMSSD
	Low-PSS	High-PSS	Low-PSS	High-PSS	Low-PSS	High-PSS	Low-PSS	High-PSS
Age	−0.45***	−0.45***	−0.41***	−0.38***	−0.09*	−0.17***	−0.39***	−0.37***
Gender (Women/men)	0.26***	0.26***	0.08*	0.15**	0.22***	0.20***	0.07	0.13**
BMI	0.02	0.01	−0.06	−0.01	0.08*	0.01	0.03	−0.06
Smoking status (No/ yes)	0.02	0.02	−0.003	−0.07	0.05	−0.05	0.05	0.08
Physical activity (Low/ high)	0.05	0.05	−0.03	0.10*	−0.09*	−0.06	0.03	0.15***
Total cholesterol	−0.13**	−0.15***	−0.11**	−0.07	−0.05	−0.09*	−0.16***	−0.11*
Triglyceride	−0.18**	−0.10*	−0.21***	−0.07	0.01	−0.03	−0.20***	−0.15**
Fasting glucose	−0.20***	−0.20***	−0.22***	−0.20***	−0.01	−0.04	−0.22***	−0.22***
BAI	−0.04	−0.15**	−0.06	−0.14**	0.01	−0.01	−0.06	−0.13**
BDI	−0.03	−0.05	0.01	−0.03	−0.06	−0.01	0.01	−0.04

Data are represented as correlation coefficient values.

First category in parenthesis is the reference group.

Physical activity levels were classified as 0–2 times per week (low)/ ≥3 times per week (high).

Low- and high-PSS groups were determined by a median split at a PSS score of 21.

Pearson correlation was used to evaluate the correlation between serum total cholesterol and HRV indices in the High-PSS group, and the others were analyzed by Spearman correlation.

Abbreviations: BAI, Beck Anxiety Inventory; BDI, Beck Depression-Inventory-II; BMI, body mass index; PSS, Perceived Stress Scale; HRV, heart rate variability; LF, low frequency power; HF, high frequency power; LF/HF, ratio of LF to HF; RMSSD, the root mean square of successive heartbeat interval differences.

*p < 0.05; **p < 0.01; ***p < 0.001.