Night owls may be at greater risk for depression than early birds.
Previous studies have found a link between a person’s unique circadian rhythm, or chronotype, and depression, but none were able to tell whether sleep habits were a cause or an effect of the disease. This new prospective study, in the Journal of Psychiatric Research, is a step closer to establishing causality.
Researchers gathered health and behavioral data on 32,740 women whose average age was 55. Each categorized herself as a definite evening or morning type, a somewhat morning or evening type, or neither. All were free of depression at the start of the study, and over the following four years 2,581 of them developed depression, defined by antidepressant use or a clinical diagnosis.
After adjusting for marital status, living alone, being retired, alcohol consumption and other variables, the researchers found that compared to the intermediate types, morning people were 12 percent less likely to develop depression, and night owls 6 percent more likely to develop it. The relationship was linear: the more a woman tended toward the night-owl type, the more likely she was to develop depression.
“The effect is modest, a modest association for chronotype and incident depression,” said the
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