A team of Iranian researchers recently published a meta-analysis seeking to determine what, if any, association there may be between low Vitamin D levels and ADHD in children and adolescents.
Combining the results from thirteen studies with 10,334 participants, they found that youth with ADHD had “modest but significant” lower serum concentrations of 25-hydroxyvitamin D than normally developing children. The weighted mean difference was just under 7 nanograms per milliliter. The odds of obtaining such a result by chance would be less than one in a thousand (p < .001). There was little to no sign of publication bias. Between-study heterogeneity, however, was very high (I2 = 94).
These results suggest an association. But are low serum levels of Vitamin D a cause or effect of ADHD? Causation is vastly more difficult to establish than association. To begin to tease this out, the researchers identified four prospective studies that compared maternal Vitamin D levels with the subsequent development of ADHD symptoms in their children. Two of these used maternal serum levels, and two used umbilical cord serum levels. Together, these studies found that low maternal Vitamin D levels were associated with a 40% higher risk of ADHD in their children. Whether maternal serum or umbilical cord serum measurements were used had little or no effect on the outcome. Study heterogeneity was negligible. But the authors noted that this result “should be considered with caution” because it was heavily dependent on one of the prospective studies included in the analysis. All of which suggests a need for further prospective studies.
In the meantime, the authors suggest it would be prudent to increase sun exposure and Vitamin D supplementation given the prevalence of Vitamin D deficiency.
Yadollah Khoshbakht, Reza Bidaki, and Amin Salehi-Abargouei, “Vitamin D Status and Attention Deficit Hyperactivity Disorder: A Systematic Review and Meta-Analysis of Observational Studies,” Advances in Nutrition, vol. 9, issue 1, p. 9-20 (2018).