Fewer children have attention-deficit hyperactivity disorder (ADHD) where sunshine is plentiful, according to new research published in the journal Biological Psychiatry
ADHD is a condition characterized by high levels of distraction, impulsiveness, an inability to remain still and a tendency to be abnormally talkative.
This is the first study showing a statistically significant link between sunshine — measured as “solar intensity” — and the disorder, said L. Eugene Arnold, M.D., an ADHD expert and professor emeritus of psychiatry at Ohio State University.
The study ruled out several other possible explanations for the geographic variability including low birth weight, infant mortality levels, socioeconomic differences and latitude.
However, the researchers noted that other unknown factors could contribute to lower cases of ADHD in sunny spots.
For example, some sunny states in the southeast — including Florida — don’t have low rates of ADHD.
And not-so-sunny Illinois had an ADHD rate that was 6.2 percent, identical to California’s. Ohio’s rate, according to that same survey, was more than 13 percent.
Study leader Martijn Arns of Utrecht University in the Netherlands speculated that our biological clocks may help explain the apparent connection with sun exposure. As people around the world spend more time in front of computers and hand-held devices in the hours leading up to bedtime, they’re getting less quality sleep.
“The blue light (from the devices) prevents the onset of melatonin, which naturally tells us to go to sleep,” Arnold said.
In theory, plenty of sunlight in some places could help make up for that, he said.
Arns said that vitamin D levels are an unlikely explanation for the results, since another recent large study showed no relationship between the vitamin and behavioral problems in children.
Prior research has found genetic predispositions that lead to ADHD, but researchers continue to investigate other factors that might contribute to the disorder.
“Nobody has thought to look at this before. I think it’s a very important paper,” said Russell Barkley, M.D., an ADHD expert and clinical professor of psychiatry and pediatrics at the Medical University of South Carolina, who was not involved in the sunlight research.
Problems with sleeping are known to interfere with attentiveness, so the idea behind the study makes sense, Barkley said.
He said the results could prove significant for children and clinicians if more research in a controlled setting shows a solid connection between light exposure and ADHD symptoms.
Source: Biological Psychiatry