Shift work appears to reduce heart rate variability (HRV) in males but not in females, according to a recent study, suggesting an imbalance in the autonomic nervous system. Researchers recruited 665 adult blue-collar workers (56.1 percent male) in whom the time and frequency domains of HRV were measured during sleep. Multiple linear regression analysis was performed to compare HRV in day and shift workers. In the study cohort, majority were day workers (n=543) while the rest were split between night shift work (n=74) and non-night shift work (n=48). Night shift workers were more likely to be male and in manufacturing or transportation industries. In a linear regression model adjusted for covariates such as body mass index, smoking, sex, age and alcohol consumption, shift work was not significantly associated with HRV parameters except for the natural log (ln) of very low-frequency spectral power (VLF; B, –0.21; 95 percent CI, –0.36 to 0.05). This indicated that shift workers had a 23-percent lower VLF than day workers. Non-night shift workers also had significantly lower ln VLF than day workers (B, –0.32; –0.55 to 0.09). The difference in ln VLF between night shift and day workers did not reach significance. Notably, there appeared to be a significant interaction of HRV parameters with sex. In male shift workers, ln VLF (B, –0.27; –0.46 to 0.09), ln total power (B, –0.61; –1.20 to 0.03) and the root mean square of successive differences (B, –7.83; –14.28 to 1.38) were significantly lower than in male day workers. In females, only the ratio between the low- and high-frequency spectral powers were significantly varied, the values of which were lower in shift workers (B, –0.29; –0.54 to 0.03). Source
