Increases in the rates of childhood ADHD over the past two decades have lead to speculation that calcitriol deficiency (e.g., secondary to the increased use of sunscreen and/or increases in sedentary, indoor lifestyles in children) plays a causal/contributory role in the etiology of ADHD. To date, evidence of a direct link is lacking. One study showed higher maternal circulating Vitamin D levels in pregnancy are associated with lower risk of developing ADHD-like symptoms in childhood. On the other hand, another study did not replicate the above association, and a prospective study using umbilical cord samples stored at the time of birth reported no difference in serum vitamin D levels between ADHD group versus healthy controls. In terms of clinical trials, one randomized double blind study among adults with ADHD reported a beneficial effect of the intervention, measured with the Conners Adult ADHR rating scale, in comparison with placebo, but the intervention included the combination of vitamin D and several other micronutrients. An analysis of moderators of a positive response to ADHD behaviors did not reveal a significant predictive effect of vitamin D.