Heart rate variability in middle-aged adults: Use of Sasang typology to distinguish individuals susceptible to stress

While stress is known to cause many diseases, there is no established method to determine individuals vulnerable to stress. Sasang typology categorizes humans into four Sasang types (So-Eum, Tae-Eum, So-Yang, and Tae-Yang), which have unique pathophysiologies because of their differential susceptibilities to specific stimuli, including stress. The purpose of this study was to determine if Sasang typology can be used identify individuals who are vulnerable to stress by evaluation of heart rate variability (HRV). This was a cross-sectional study. A total of 399 healthy men and women aged 30 to 49 years were recruited. Physical examinations for stress included HRV measurement and blood tests. The subjects also completed questionnaires about psychological stress, self-awareness, and lifestyle. HRV was analyzed using frequency-domain analysis. Subjects were divided into So-Eum (SE) and non-So-Eum (non-SE) groups according to their diagnosis. The weight and body mass index in the SE group were significantly lower than those in the non-SE group (both, P = .000). There were no significant between-group differences in any other demographic variables. In HRV analysis, the normalized high frequency (nHF) was higher (P = .008) while the normalized low frequency (nLF; P = .008) and LF:HF ratio (LF/HF; P = .002) were lower in the SE group than in the non-SE group. Although there was no difference in variables affecting HRV, HRV values were significantly different between groups. The LF/HF value for the SE group was at the lower limit of the normal range, although there were no associated clinical problems. These findings suggest that individuals with the SE type are more susceptible to stress than those with the other types. Thus, middle-aged individuals who are vulnerable to stress can be identified using Sasang typology.