Updated 04 July 2014

Sunny regions have lower ADHD rates

Research indicates that regions that get the most sun have rates of ADHD diagnoses about half as high as regions that get the least.


Sunny days can be a big distraction for those who are tethered to their desks, but a new study suggests that sunlight may actually lower the prevalence of attention-deficit/hyperactivity disorder (ADHD).

Scientists mapped the number of ADHD diagnoses across the United States and in nine other countries. They compared those rates to the intensity of sunlight those regions receive year-round.

Regions that got the most sun had rates of ADHD diagnoses that were about half as high as regions that got the least, according to the research.

"The maps line up almost perfectly," said study author Martijn Arns, director of Brain clinics, in the department of experimental psychology at Utrecht University in Nijmegen, Netherlands.

In the United States, the sunniest states were in the Southwest and West and included Arizona, California, Colorado, Nevada, New Mexico and Utah. Rates of ADHD diagnoses in those states ranged from 6% to 8%. In the darkest states, which included a swath of the Northeast, rates of ADHD ranged from 10% to 14%.

The relationship between ADHD and sunlight held steady even after researchers adjusted their data to control for other factors that might account for differing rates of ADHD diagnoses, such as race, poverty and the male-to-female ratio in each area.

The role of vitamin D

Researchers even considered whether vitamin D, which is produced in the body after exposure to sunlight, might account for the differences, but they said a prior study ruled that out.

They also examined whether more sunlight might be tied to lower rates of other kinds of mental disorders, including depression and autism. It wasn't.

The researchers admitted that the link could just be a coincidence, and there isn't necessarily a cause-and-effect relationship between sunny climates and lower rates of ADHD diagnosis. But since some children and adults with ADHD have disrupted body clocks, which are regulated by light, they believe the relationship deserves further investigation.

Arns said about 80% of adults and about one-third of children with ADHD have trouble falling asleep at night. Some studies have found that these night-owl tendencies are driven by a delayed peak in the sleep hormone melatonin.

Melatonin seems to be especially disrupted by the blue wavelengths of visible light, Arns said. Energy-saving LED light bulbs, as well as the screens of tablets, smartphones and computers emit blue light. When people use those devices in the evening, it can delay melatonin release and disrupt sleep.

Body clocks on track

But Arns said people who live in sunny climates may get some natural protection from this sleep upset because they get a healthy dose of bright light in the morning, which keeps their body clocks on track.

He's currently exploring ways to test his theory.

An expert who was not involved in the study, which was published in the journal Biological Psychiatry, said he's not sure melatonin is the best explanation.

Children in sunny climates may spend more time playing outside, for example, said Dr Andrew Adesman, chief of developmental and behavioural paediatrics at the Steven & Alexandra Cohen Children's Medical Centre in New Hyde Park, New York.

"There's a small but growing literature talking about exercise as a way to moderate ADHD and hyperactivity," Adesman said. "There could be other variables that are responsible."

More information

Visit the US Centres for Disease Control and Prevention for more on ADHD.

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Dr. Shabeer Ahmed Jeeva is a specialist psychiatrist who has been practicing child and adult psychiatry for 30 years. He has vast experience in treating ADHD, and is also an ADHD patient himself. Dr. Jeeva trained and practiced in Canada as a child and adult psychiatrist and had lived there for 25 years. He had attended medical school at the Royal College of Surgeons in Dublin, Ireland (1970-1976). His professional experience and accreditation includes: Psychiatric residency at the University of Ottawa (Canada), Child Psychiatry fellowship at the University of Ottawa (Canada), Diploma in Psychiatry at the University of Ottawa (Canada), and Fellow of the Royal College of Physicians in Canada. Visit his website at:

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