Cognitive ability in childhood and the chronicity and suicidality of depression.

BACKGROUND: There is inconsistent evidence regarding the influence of general cognitive abilities on the long-term course of depression. AIMS: To investigate the association between general childhood cognitive abilities and adult depression outcomes.
METHOD: We conducted a cohort study using data from 633 participants in the New England Family Study with lifetime depression. Cognitive abilities at age 7 were measured using the Wechsler Intelligence Scale for Children. Depression outcomes were assessed using structured diagnostic interviews administered up to four times in adulthood between ages 17 and 49.
RESULTS: In analyses adjusting for demographic factors and parental psychiatric illness, low general cognitive ability (i.e. IQ<85 v. IQ>115) was associated with recurrent depressive episodes (odds ratio (OR) = 2.19, 95% CI 1.20-4.00), longer episode duration (rate ratio 4.21, 95% CI 2.24-7.94), admission to hospital for depression (OR = 3.65, 95% CI 1.34-9.93) and suicide ideation (OR = 3.79, 95% CI 1.79-8.02) and attempt (OR = 4.94, 95% CI 1.67-14.55).
CONCLUSIONS: Variation in cognitive abilities, predominantly within the normal range and established early in childhood, may confer long-term vulnerability for prolonged and severe depression. The mechanisms underlying this vulnerability need to be established to improve the prognosis of depression among individuals with lower cognitive abilities. © The Royal College of Psychiatrists 2016.