Newborns with vitamin D deficiency had a 44% increased risk for schizophrenia in later life compared with those with normal vitamin D levels, according to study data reported in Scientific Reports.
“Much of the attention in schizophrenia research has been focused on modifiable factors early in life with the goal of reducing the burden of this disease,” John J. McGrath, MD, PhD, from the University of Queensland and Queensland Centre for Mental Health Research, Australia, said in a press release. “Previous research identified an increased risk of schizophrenia associated with being born in winter or spring and living in a high-latitude country, such as Denmark. We hypothesized that low vitamin D levels in pregnant women due to a lack of sun exposure during winter months might underlie this risk and investigated the association between vitamin D deficiency and risk of schizophrenia.”
To determine whether prenatal vitamin D deficiency affected the risk for schizophrenia diagnoses later in life, researchers from Denmark and Australia examined concentrations of 25 hydroxyvitamin D (25OHD) in neonatal dried blood samples from a Danish case-control study encompassing 2,602 people.
They derived quintiles for 25OHD based on the control sample, calculating incidence rate ratios (IRRs) to determine the link between neonatal 25OHD concentration and schizophrenia risk. In a previous study, McGrath and colleagues found that the lowest and highest quintiles were associated with increased risks for schizophrenia compared with the fourth quintile; therefore, the current study prespecified the fourth quartile as the reference category.
Neonatal vitamin D deficiency was associated with an increased risk for schizophrenia in later life, according to study findings.
The investigators also evaluated statistical models that combined 25OHD concentration and the schizophrenia polygenic risk score in a sample that combined the new sample with a previous study of 3,464 samples assayed and genotyped between 2008-2013.
The results showed that vitamin D deficiency was associated with a 44% increased risk for schizophrenia. Compared to the reference category, participants in the lowest quintile with 25OHD below 20.4 nmol/L — consistent with standard definitions of vitamin D deficiency — were at higher risk for schizophrenia in later years (IRR = 1.44; 95% CI, 1.12-1.85). None of the other comparisons were significant, according to the study.
“With respect to the population-attributable fraction, optimizing neonatal 25OHD status (ie, shifting the population to optimal levels within the reference category) could account for 8.4% of the incidence of schizophrenia in this setting,” the researchers wrote.
In the combined sample, McGrath and colleagues found that participants in the lowest and second-lowest 25OHD quintiles were at greater risk for schizophrenia compared with the reference fourth quintile (IRR = 1.52, 95% CI, 1.2-1.93; IRR = 1.31, 95% CI, 1.03-1.67). In addition, analyses confirmed that 25OHD concentration affected schizophrenia risk when included as a continuous variable (IRR = 0.92; 95% CI, 0.86-0.99), with higher 25OHD linked to lower risk.
“This study provides another piece of the jigsaw puzzle – and helps us understand what might cause schizophrenia. We have more studies underway to follow up these clues,” McGrath told Healio.com/Psychiatry. “While we wait for more data, pregnant women who are at risk of vitamin D deficiency (eg, during winter, high latitudes, those who do not go out in the sun) should talk to their local doctors to get the best advice on prenatal nutrition.” – by Savannah Demko
Disclosure: The authors report no relevant financial disclosures.