Genetically Proxied Diurnal Preference, Sleep Timing, and Risk of Major Depressive Disorder.
Level 3 - non-randomized controlled study
Two-sample Mendelian randomization study using large-scale genome-wide association data.
PubMed 34037671 · doi:10.1001/jamapsychiatry.2021.0959
What was done
A two-sample Mendelian randomization study evaluated the potential causal association between morning diurnal preference and major depressive disorder (MDD). Genetic proxies included up to 340 loci from meta-analyses of UK Biobank and 23andMe cohorts (n = 697,828), scaled against accelerometer-derived sleep midpoint measurements (n = 85,502 in UK Biobank). These variants were applied to MDD genome-wide association data from the Psychiatric Genomics Consortium and UK Biobank (170,756 MDD cases and 329,443 controls). The primary analysis used the inverse-variance weighted method to estimate the association of a 1-hour earlier sleep midpoint with MDD risk.
What was found
Genetically proxied morning diurnal preference corresponding to a 1-hour earlier sleep midpoint was associated with a 23% lower risk of MDD (odds ratio [OR], 0.77; 95% CI, 0.63–0.94; P = .01). The association remained similar when restricted to stringently defined MDD in the Psychiatric Genomics Consortium (OR, 0.73; 95% CI, 0.54–1.00; P = .05), but was not statistically significant when defined by hospital billing codes in UK Biobank (OR, 0.64; 95% CI, 0.39–1.06; P = .08). Sensitivity analyses indicated no significant horizontal pleiotropy (MR-Egger intercept [SE], 0.00 [0.001]; P = .66).
Why it matters
This study provides genetic instrumental variable evidence that earlier sleep timing may causally protect against major depressive disorder, identifying circadian alignment as a potential target for preventive interventions.
Limits
All analyses were restricted to individuals of European ancestry. Mendelian randomization reflects lifelong genetically proxied exposure rather than discrete behavioral interventions, some depression definitions relied on self-report, and the subgroup using hospital billing codes was underpowered.