ADHD is a condition characterised by high levels of distraction, impulsiveness, an inability to remain still and a tendency to be abnormally talkative.
While there is no clear cause for ADHD, scientists have identified a number of risk factors for an ADHD diagnosis: genetics, low birth weight, pre-term birth, and exposure to environmental toxins like lead have all been contributed to ADHD.
According to Martjin Arns and his team from Utrecht University in the Netherlands, sunshine (or lack thereof) is also a risk factor for ADHD. The average worldwide prevalence of ADHD is estimated at 5-7%, but when plotted on a map, there are very distinct regions with higher prevalence — and these areas have lower sunlight intensity.
The researchers ruled out a number of other possible explanations for the geographic variability including low birth-weight, infant mortality levels, socioeconomic differences and latitude. But they said other unknown factors could contribute to lower incidence in sunny spots. Sunny states in the southeast, including Florida, don’t have low rates of ADHD. And often-less-than-sunny Illinois had an ADHD rate that was 6.2 percent — identical to California’s — according to a 2007 federal survey. Ohio’s rate, according to that same survey, was more than 13 percent.
Arns speculated that our biological clocks could 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,” said L. Eugene Arnold, an ADHD expert who worked on the study and a professor emeritus of psychiatry at Ohio State University. In theory, ample sunlight in some places could help make up for that, he said.
Arns wrote that vitamin D levels are an unlikely explanation for geographical variability, given another recent large study that showed no relationship between the vitamin and behavioural problems in children.
This study begs a lot of questions. Further research is definitely needed, so don’t consider a cross-country move, just to get to warmer weather.