Context: Clues from the epidemiology of schizophrenia suggest that low levels of developmental vitamin D may be associated with increased risk of schizophrenia.
Objective: To directly examine the association between neonatal vitamin D status and risk of schizophrenia.
Design: Individually matched case-control study drawn from a population-based cohort.
Setting: Danish national health registers and neonatal biobank.
Participants: A total of 424 individuals with schizophrenia and 424 controls matched for sex and date of birth.
Main outcome measures: The concentration of 25 hydroxyvitamin D(3) (25[OH]D3) was assessed from neonatal dried blood samples using a highly sensitive liquid chromatography tandem mass spectroscopy method. Relative risks were calculated for the matched pairs when examined for quintiles of 25(OH)D3.
Results: Compared with neonates in the fourth quintile (with 25[OH]D3 concentrations between 40.5 and 50.9 nmol/L), those in each of the lower 3 quintiles had a significantly increased risk of schizophrenia (2-fold elevated risk). Unexpectedly, those in the highest quintile also had a significantly increased risk of schizophrenia. Based on this analysis, the population-attributable fraction associated with neonatal vitamin D status was 44%. The relationship was not explained by a wide range of potential confounding or interacting variables.
Conclusions: Both low and high concentrations of neonatal vitamin D are associated with increased risk of schizophrenia, and it is feasible that this exposure could contribute to a sizeable proportion of cases in Denmark. In light of the substantial public health implications of this finding, there is an urgent need to further explore the effect of vitamin D status on brain development and later mental health.