Twin studies of subjective sleep quality and sleep duration, and their behavioral correlates: Systematic review and meta-analysis of heritability estimates.

Twin studies have shown that a substantial proportion of the variance for sleep variables is due to genetic factors. However, there is still considerable heterogeneity among research reports. Our main objectives were to: 1) Review the twin literature regarding sleep quality and duration, as well as their behavioural correlates; 2) Estimate the mean heritability of subjective sleep quality and sleep duration; 3) Assess heterogeneity among studies on these topics; and 4) Search for moderator variables. Two parallel meta-analyses were carried out for sleep quality and sleep duration. Seventeen articles were included in the meta-analysis. Mean MZ correlations were consistently higher than DZ correlations. A mean heritability of 0.31 (95% CI: 0.20, 0.41) was found for subjective sleep quality (range: 0-0.43) and 0.38 (95% CI: 0.16, 0.56) for sleep duration (range: 0-1). Heterogeneity indexes were significant for both sleep quality (I2 = 98.77, p < .001) and sleep duration (I2 = 99.73, p < .001). The high heterogeneity warrants further research considering possible moderators that may affect heritability.