Reply to: The Geographic Variation in the Prevalence of Attention-Deficit/Hyperactivity Disorder the United States is Likely Due to Geographical Variations of Solar Ultraviolet B Doses and Race

      In his correspondence, Dr. Grant proposes an alternative explanation for our findings on the association between attention-deficit/hyperactivity disorder (ADHD) prevalence (PREV) and solar intensity (SI) (
      • Grant W.B.
      The geographic variation in the prevalence of attention-deficit/hyperactivity disorder in the United States is likely due to geographical variations of solar ultraviolet b doses and race.
      ). Whereas in our article we argue that the most likely mechanism is through effects on the circadian system, Dr. Grant proposes that the explanation of solar-related increases of vitamin D should be reconsidered. Indeed, the SI measure used in our analysis has both effects on the circadian system (via 464–484 nm blue light), as well as solar radiation changing 7-dehydroxycholesterol in the skin to vitamin D (via 290–315 nm ultraviolet B light). In our correlational analysis, these 2 effects could not be separated. We considered the vitamin D possibility before settling on circadian rhythm entrainment as the most likely hypothesis.
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        • Grant W.B.
        The geographic variation in the prevalence of attention-deficit/hyperactivity disorder in the United States is likely due to geographical variations of solar ultraviolet b doses and race.
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