Acute stress might increase short-term heart rate variability and blood pressure variability (BPV); however, chronic stress would not alter short-term BPV in animal models.

To examine the association of psychological stress with long-term BPV in young male humans.

We prospectively examined the association of chronic psychological stress with long-term BPV in 1112 healthy military males, averaged 32.2 years from the cardiorespiratory fitness and hospitalization events in armed forces study in Taiwan. Psychological stress was quantitatively evaluated with the Brief Symptom Rating Scale (BSRS-5), from the least symptom of 0 to the most severe of 20, and the five components of anxiety, insomnia, depression, interpersonal sensitivity, and hostility (the severity score in each component from 0 to 4). Long-term BPV was assessed by standard deviation (SD) for systolic and diastolic blood pressure (SBP and DBP), and average real variability (ARV), defined as the average absolute difference between successive measurements of SBP or DBP, across four visits in the study period from 2012 to 2018 (2012-14, 2014-15, 2015-16, and 2016-18).

The results of multivariable linear regressions showed that there were no correlations of the BSRS-5 score with SD_SBP, SD_DBP, ARV_SBP, and ARV_DBP after adjusting for all the covariates [β(SE): -0.022 (0.024), -0.023 (0.026), -0.001 (0.018), and 0.001 (0.020), respectively; P > 0.05 for all]. In addition, there were also no correlations between each component of the BSRS score and the long-term BPV indexes.

Our findings suggest that chronic psychological stress might not be associated with long-term BPV in military young male humans.

Psychological stress is related to activation of the sympathetic nervous system and production of norepinephrine and epinephrine from the adrenal glands, leading to elevated blood pressure. Previous studies have shown that psychological stress, particularly chronic stress, may cause the development of hypertension[1]. To our knowledge, psychological stress is subjective and complicated in human beings. An experiment in mice demonstrated that acute stress might result in increased short-term heart rate variability and blood pressure variability (BPV); however, chronic stress would not alter short-term BPV[2]. Whether chronic mental stress is associated with long-term BPV remains unclear in human beings. Therefore, we investigated such association in a military cohort of young male adults.

Table 1 shows the baseline profiles of the study participants. The age, body stature, hemodynamic status, and serum lipid profiles were similar between the normal subjects and those with stress. Those who had chronic mental stress were found with a lower level of physical activity and higher prevalence of alcohol drinking. Table 2 shows the results of multivariable linear regressions. In the unadjusted model, there were no correlations between the BSRS score and each component with SD and ARV for SBP and DBP variability, except that interpersonal sensitivity was borderline significantly and negatively correlated with SD_SBP [β(SE): -0.010 (0.005), P = 0.07]. After adjusting for the covariates in model 1, the associations of the BSRS score and each component with the long-term BPV indexes did not change a lot and remained insignificant. The correlation between interpersonal sensitivity and SD_SBP was just mildly reduced [β(SE): -0.009 (0.005), P = 0.09].

We found that young military male adults with chronic psychological stress had a higher prevalence of alcohol drinking and less physical activity, reflecting that the BSRS score may be reliable for the evaluation of mental stress[15,16]. The principal finding was that there was no association of chronic psychological stress and its pivotal domains with long-term BPV in young military male adults. A prior study in mice has revealed that acute stress but not chronic stress was associated with short-term BPV (within an hour measurement)[2]. In addition, acute stressors on human beings could lead to an elevation of blood pressure levels and the effect persisted for a while[17]. This finding may make short-term BPV less sensitive to stress as compared with heart rate variability in human beings and similarly in the mouse model[2,18]. Notably, this study was the first one providing the evidence for a null association between chronic psychological stress and long-term BPV.

The results from the mouse experiment also demonstrated that acute stress could increase short-term BPV, which was likely due to sympathetic nervous system activation and baroreflex control impairment[2]. On the contrary, chronic stress might reduce short-term BPV due to the coordination of sympathetic activation and physiological response to the vascular alterations in hypertension[19,20]. Our findings also revealed that the BSRS-5 score was inversely correlated to almost all of the long-term BPV indexes in young male adults despite insignificance. This tendency of inverse association might differ by the components of BSRS-5 score, which was in line with anxiety, depression, and interpersonal sensitivity but contradicted to insomnia.

There were some strengths in this study. First, the questionnaire for BSRS-5, physical examinations, and blood pressure measurements were all performed standardly and in a strict manner at the clinic visit. Second, many unmeasured confounders had been controlled at baseline since daily life of the military such as deployment, physical activity, and stress sources were similar across troops. On the contrary, there were several limitations in this study. First, the results were obtained from the male subjects and might be inappropriately applied for the female subjects. Second, the study had a follow-up period for merely 7 years when the prevalence of hypertension remained low, possibly reducing the degree of association between psychological stress and BPV. Third, we used only a single measurement of blood pressure on each visit, which might be susceptible to change by cigarettes, coffee, and indoor temperature. Although the objective environment and the detailed preparations for blood pressure assessment have been regulated, other confounders such as white coat hypertension might be present in some subjects, possibly resulting in a bias. Lastly, there were only four occasions (every two years in interval) for blood pressure measurement, which would cause wide variations of SD and ARV, resulting in reduced associations for psychological stress. The interval of blood pressure measurement had a long time scale (years instead of months). Therefore, it may promote further studies to either confirm or dispute the conclusions.

In conclusion, our findings suggest that chronic psychological stress is not associated with long-term BPV in young males. In addition, this study is the first one revealing a null association between each chronic stress component and long-term BPV in human beings. It is necessary to see whether there might be a change for the relationship with long-term BPV in a longer follow-up when the prevalence of hypertension increases with ageing.