Body mass index trajectories in childhood and adolescence - Risk for non-affective psychosis

Abstract Background Underweight in early adulthood increases risk for schizophrenia, but the effect of early childhood underweight on psychosis risk is not well known. Methods We studied whether underweight or overweight in childhood and adolescence increases risk for non-affective psychosis or other psychiatric disorders in a population-based cohort study ‘Cardiovascular Risk in Young Finns’. Body mass index (BMI) trajectories were recorded in the years 1980, 1983 and 1986 (in 3–18 years of age), before the first hospitalization due to a psychiatric disorder. BMI was categorized as underweight, normal weight or overweight, using the BMI classification for children and adolescents. We formed DSM-IV based diagnostic groups of non-affective psychosis (n = 69, including a schizophrenia subgroup, n = 41) and affective disorders (i.e. mood and anxiety disorders, n = 112) based on the Care Register for Health Care. Groups were compared with subjects with no psychiatric diagnoses (n = 3310). Sex, age, low birthweight and mother's mental disorders were included in the analyses. Results Underweight, but not overweight, independently predicted later development of non-affective psychosis. The risk of psychosis was over two-fold (relative risk (RR) [95% CI] 2.31 [1.2–4.4]) and of schizophrenia nearly 2.5-fold (RR 2.44 [1.03–5.8]) after underweight in childhood/adolescence. Underweight or overweight in childhood and adolescence was not associated with mood or anxiety disorders. Conclusions These results support the hypothesis of non-affective psychosis as a neurodevelopmental disorder with somatic manifestations throughout childhood and adolescence.