Tegegne BS, et al. - Researchers determined to what extent individual differences in heart rate variability (HRV) in the general population can be explained by a broad range of demographic (age, sex), lifestyle (physical activity, smoking, alcohol use) and psychosocial factors (stress, social wellbeing, neuroticism), using baseline data of 10 second electrocardiograms (ECG) from the Lifelines cohort study (n=149,205;58.7% female; mean age [SD]: 44.6[13.2] year) and hierarchical linear regression models adjusting for potential confounding effects of medication use, disease and body mass index. A strong decline in HRV was noted with age, and women consistently exhibited higher HRV. In this very large general population cohort, almost one fifth of the individual differences in HRV was explained by age and sex. A negligible additional contribution of lifestyle and psychosocial factors was also observed.