Insomnia as a risk factor for the development of depression and anxiety in primary care: a matched population-based cohort study

BACKGROUND: While insomnia, depression and anxiety disorders are most frequently diagnosed and treated in primary care, the longitudinal relationship between these phenomena remains elusive in this setting. The present study aimed to quantify the association of registered insomnia with subsequent depression or anxiety in primary care. METHODS: A matched population-based cohort study was conducted using International Classification of Primary Care (ICPC) and Anatomical Therapeutic Classification (ATC) codes extracted from medical records of 84 Dutch general practices. Patients without documented psychological or social problems, aged 18 to 65 years, with a registered insomnia diagnosis (ICPC: P06) or prescribed sleep medication (ATC: N05CD, N05CF, N05CH) were matched 1:1 to healthy controls on sex, year of birth, and general practice. Controls could be used more than once. The primary outcome measure was depression (ICPC: P03, P76, P76.02) or anxiety (ICPC: P01, P74, P74.01, P74.02) registration up to five years after the insomnia diagnosis. RESULTS: Patients with insomnia between 1 January 2010 and 1 January 2015 (n = 1535) and the control group (n = 1502) were followed for five years after the insomnia diagnosis. Patients with insomnia had a higher risk of depression or anxiety (odds ratio (OR) = 1.53, 95% confidence interval (CI) [1.18-1.98]). CONCLUSIONS: Patients with an insomnia diagnosis in primary care were at higher risk to develop depression or anxiety compared to healthy controls. This finding identifies insomnia as a potential marker for early detection and prevention of depression and anxiety in primary care.