(HealthDay News) – Sunny areas of the world have a lower prevalence of attention-deficit/hyperactivity disorder (ADHD), according to a study published in the Oct. 15 issue of Biological Psychiatry.

Noting that the prevalence of ADHD worldwide varies by region, Martijn Arns, PhD, from Research Institute Brainclinics in Nijmegen, Netherlands, and colleagues examined the association between the prevalence of ADHD and solar intensity using data from the United States and nine other countries.

The researchers found that solar intensity could explain 34–57% of the variance in the prevalence of ADHD. Areas with high solar intensity had a lower prevalence of ADHD, even after controlling for factors such as low birth weight and average income, but there was no association seen between solar intensity and the prevalence of autism spectrum disorders or major depressive disorder.

“In this study we found a lower prevalence of ADHD in areas with high solar intensity for both U.S. and non-U.S. data,” Arns and colleagues conclude. “The preventative effect of high solar intensity might be related to an improvement of circadian clock disturbances, which have recently been associated with ADHD.”

One author disclosed financial ties to the pharmaceutical industry.

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