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.