Evolutionary Psychiatry

The hunt for evolutionary solutions to contemporary mental health problems.

Sunlight and ADHD

Evidence that bright sunlight can ameliorate symptoms of ADHD

Evolutionary medicine is a way of looking at modern disease through the lens of our ancestral past. What sorts of differences in our modern lifestyle are causing problems with our bodies and brains that are primarily evolved for a Stone Age lifestyle? While I focus a great deal on diet, sunlight exposure and sleep are also extremely important to our health. A recent study (brought to my attention by Dr. Paul Whiteley) probes a remarkable association between sunlight intensity in a region and the diagnosis of ADHD.

ADHD more than many psychiatric diagnoses is what I would consider a “disease of civilization.” Nutrient deficiencies and food allergies have been shown to exacerbate the symptoms in some children, as well as sleep deficits. In addition, our expectation that everyone from young children in school to adults working on computers sit around paying close attention all day seems entirely modern. Certainly in the distant past young children played and hunted and gathered alongside their parents, and humans got to do a variety of tasks throughout the day, a lot of it in the sunshine and fresh air. 

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ADHD begins in childhood, with 5.3% of children worldwide affected. Genes are important as well as prenatal environment and, as I alluded to before, nutrition. The new study suggests that amount of sunshine in the environment could also play a significant role in changing the risk of having symptoms of the disorder. 78% of unmedicated adults and a third of unmedicated children with ADHD have a certain kind of unexplained insomnia. It is difficult for them to get to sleep, and their circadian rhythms seem to be delayed. Genes controlling melatonin signaling and circadian rhythm clock proteins are also known to be abnormal in some people with ADHD. 

Working on getting a good night’s sleep is an integral part of the treatment of ADHD, as even people without ADHD develop impaired attention and increased impulsive behaviors when sleep-deprived. Morning light therapy, melatonin supplementation, iron supplementation (can help restless legs if iron is low), and surgery to remove enlarged tonsils and adenoids (which can cause sleep apnea in children) have all been shown to be beneficial. Since all these sleep problems exist in children who are unmedicated, stimulant medicine is not the only cause of sleep problems in ADHD. However, stimulants can worsen sleep which is one of the downsides of using medication.

In our environments, bright sunlight is known to enhance and reinforce our own natural circadian rhythms, helping us to be alert during the day and to sleep better at night. Could bright sunlight, then, reduce the symptoms of ADHD? Researchers compared two datasets, one from the CDC mapping the prevalence of ADHD diagnosis in the United States, and a second from the National Renewable Energy Laboratory showing average sun intensity.

When the datasets were lined up, a higher sun intensity more or less correlated with lower rates of ADHD diagnoses. In fact, sun intensity itself could be responsible for about 34-41% of the variance in ADHD diagnoses in different areas in children in the US. The researchers did the same for two other datasets of world-wide sun intensity and non-US adult ADHD and found similar results. Of course there are other reasons for regional variability in ADHD diagnoses, but circadian rhythm is very plausibly an important factor.

The best natural way to reinforce circadian rhythm is to get some morning sunlight if you can, and avoid lights, particularly blue light common in smartphone and laptop screens, in the evening hours. These screens are particularly disruptive to circadian rhythm and signaling because they are relatively rich in the blue spectrum and are held close to the face. If you must use bright handheld or laptop devices at night, install f.lux which can remove the blue light, or wear orange blue-blocking glasses (orange safety glasses that cost around $11). It is possible that bright natural sunlight could ameliorate the effects of our digital world on our sleep cycles, lessening ADHD symptoms in sunny areas.

Emily Deans, M.D., is a psychiatrist with a practice in Massachusetts.

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