henry copeland:

Geographic variation in the prevalence of attention-deficit/hyperactivity disorder: the sunny perspective. - PubMed - NCBI

The preventative effect of high SI might be related to an improvement of circadian clock disturbances, which have recently been associated with ADHD. These findings likely apply to a substantial subgroup of ADHD patients and have major implications in our understanding of the etiology and possibly prevention of ADHD by medical professionals, schools, parents, and manufacturers of mobile devices.
- www.ncbi.nlm.nih.gov