This is a review and hypothesis paper. The authors pulled together earlier research on sleep and body clocks in people with ADHD. They did not run a new study, and they looked at both children and adults.
Their main idea is that for a large subgroup with ADHD, part of the symptoms may come from a long-running sleep problem. The cause they point to most is a body clock that runs late, so the person cannot fall asleep at a normal hour. The review reports that a late body clock shows up in most children and adults with ADHD (73 to 78%). In adults, it was found in 78% when measured with a wrist movement monitor and a test of the body's own melatonin timing.
The authors also cite a trial in 101 children who had ADHD and trouble falling asleep. The children took either melatonin (3 to 6 mg) or a dummy pill before bed for 4 weeks. The melatonin group fell asleep about 27 minutes sooner and slept about 20 minutes longer. It did not change behavior, thinking skills, or quality of life.
The authors propose a new category where sleep is checked and treated alongside ADHD. They say it is still unknown whether sleep problems fully cause ADHD symptoms, and more research is needed.
Anyone considering melatonin should talk with a clinician about their own situation.
Source: Bijlenga D, Vollebregt M, Kooij J, et al.. The role of the circadian system in the etiology and pathophysiology of ADHD: time to redefine ADHD?. ADHD Attention Deficit and Hyperactivity Disorders (2019). doi:10.1007/s12402-018-0271-z
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