Effect of the Interaction Between Depression and Sleep Disorders on Stroke Occurrence: A 17-Year Prospective Cohort Study in Korea

OBJECTIVE: Previous studies have provided inconclusive results on the association between depression and stroke risk, and the potential modifying effect of comorbid insomnia on this association remains unclear. Our study aimed to clarify the independent roles of depression and insomnia as risk factors for stroke and to investigate the possibility of an interaction effect between these two conditions on stroke incidence. METHODS: We used data from the Korean Genome and Epidemiology Study. The primary exposure was depression, measured by the Beck Depression Inventory. The secondary exposure was insomnia. The main outcome was the occurrence of stroke observed in biennial follow-up surveys. Cox proportional regression analysis was performed to estimate the effects of depression and insomnia on stroke incidence. We also conducted interaction analysis to investigate the interaction between depression and insomnia on stroke incidence. RESULTS: During 16 years of follow-up involving 3,301 individuals, we documented 172 cases of new-onset stroke (4.3 cases per 1,000 person-years). Cox proportional logistic regression analysis showed that severe depression significantly increased the risk of stroke (hazard ratio [HR]: 2.06, 95% confidence interval [CI]: 1.13-3.75), whereas mild and moderate depression did not increase this risk. Interaction analysis demonstrated that stroke risk was increased with only moderate (HR: 2.04, 95% CI: 1.04-4.00) and severe (HR: 3.01, 95% CI: 1.43-6.31) depression among individuals without insomnia. CONCLUSION: Although general depression does not significantly increase stroke risk, moderate-to-severe depression may increase this risk, particularly in individuals without insomnia.