Attention deficit hyperactivity disorder (ADHD) is among the most prevalent childhood disorders; estimates suggest that approximately five to seven percent of people worldwide may have ADHD. Since ADHD is so pervasive, researchers have a lot of data at their disposal that allows them to investigate other factors that may be correlated with higher or lower rates of ADHD diagnosis. Researcher Dr. Arns and his colleagues noticed that maps displaying the prevalence of ADHD in the United States seemed to depict a pattern: there were higher rates of ADHD in places with less sunlight.

The research team went on to analyze the relationship between solar intensity, defined as the kilowatt hours/square meters/day, and ADHD prevalence. To assess solar intensity, the team obtained maps and data from national institutes. To tally the amount of people with ADHD in a region, they used self-reports of professional diagnoses for the United States, and diagnostic assessments for other countries.

After comparing various datasets, they found that there was a relationship between solar intensity and ADHD prevalence. They state that the solar intensity theory offers an explanation for the wide range of ADHD prevalence: 34 percent to 57 percent. The researchers controlled for factors such as low birth weight, average income, and latitude, but still found that sunnier regions apparently had a “preventative effect” in regards to ADHD.

According to Dr. John Krystal, editor of Biological Psychiatry, “The reported association is intriguing, but it raises many questions that have no answers. Do sunny climates reduce the severity or prevalence of ADHD and if so, how? Do people prone to develop ADHD tend to move away from sunny climates and if so, why?”

Although more research is needed to fully investigate the nature of this connection, the findings do suggest some interesting options that could potentially mitigate problems with ADHD. For example, Dr. Arns proposes that PC, tablet, and smartphone manufacturers could implement “time-modulated color-adjustment of screens,” which would limit exposure to blue light in the evenings.

This research is published in the journal Biological Psychiatry.

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