Huang M, et al. - Researchers investigated the temporal association between depression and heart rate variability (HRV) in this longitudinal twin difference study that included 146 veteran twins (73 pairs). Independent association of lower heart rate variability at baseline with increasing depressive symptoms at follow-up was noted. The opposite longitudinal association between baseline depressive symptoms and lower heart rate variability during follow-up was noted to be less strong and was mostly explained by antidepressant medication use. Findings thereby suggest autonomic dysregulation as a risk factor for depression, rather than a consequence.

Methods

• At an academic research center, researchers performed a longitudinal, cross-lagged twin difference study, with baseline assessments from March 2002 to March 2006 (visit 1) and a 7-year follow-up (visit 2) with participants recruited from a national twin registry.
• From the Vietnam Era Twin Registry, they recruited twins (n = 166), who served in the US military during the Vietnam War, and were discordant for depression at baseline.
• They measured depressive symptoms and HRV at both visits using the Beck Depression Inventory-II (BDI-II) and 24-hour electrocardiogram monitoring, respectively.
• They examined within-pair differences in multivariable mixed-effects regression models, and calculated standardized β coefficients for both pathways to assess the direction of the association.
• In monozygotic and dizygotic twins, they evaluated the associations separately.

Results

• All participants in the final analytic sample were men (N = 146), 138 (95%) of whom were white, and the mean (SD) age was 54 (3) years at baseline.
• Across all HRV domains and models (β coefficients ranging from -0.14 to -0.29), consistent associations between visit 1 HRV and visit 2 BDI score was noted; these associations were not explained by antidepressants or other participant characteristics.
• Similar scale of the association was noted in the opposite pathway, linking visit 1 BDI score to visit 2 HRV, with β coefficients ranging from 0.05 to -0.30; however, it was largely explained by antidepressant use.
• Researchers identified significant associations in monozygotic and dizygotic twins for the path linking visit 1 HRV to visit 2 BDI score in stratified analysis by zygosity, although the links were slightly stronger in dizygotic twins.