ADHD is usually described in terms of attention problems, restlessness and impulse control. For many people with the condition, however, the body’s internal clock also runs late, and researchers say that part may be treatable. Between 73% and 78% of children and adults with ADHD fall asleep and wake up later than normal. In a few trials, treatments that moved their clocks earlier also eased ADHD symptoms.
What the review looked at
The findings come from a perspective article by Brandon Luu of the Department of Respirology at Queen’s Universityin Kingston, Ontario, and Nicholas Fabiano of the University of Ottawa. It was published in December in the journal Frontiers in Psychiatry.
The researchers reviewed earlier studies rather than carrying out a new one. They also stop short of calling ADHD a body clock disorder. Their claim is narrower: a large share of people with ADHD, though not all of them, live on a late clock. Doctors, they argue, could check for this and treat it alongside standard care.
Sleep problems are common
Insomnia and other sleep problems affect up to 80% of adults and up to 82% of children with ADHD. These problems appear even in people who have no other mental health condition.
Sleep laboratory recordings support what people report. Taking a long time to fall asleep and sleeping poorly remained linked to ADHD even after anxiety and depression were taken into account.
A body clock running 90 minutes behind
Much of the problem is timing. Everyone has a circadian rhythm, a cycle of roughly 24 hours that tells the body when to feel sleepy and when to wake up. In ADHD, that cycle tends to run late, and many people with the condition are night owls.
About three-quarters of adults whose ADHD began in childhood show measurable signs of a late clock. Their body temperature rhythm, their sleep timing and the evening rise of melatonin all run roughly 90 minutes behind those of adults without ADHD.
Melatonin release starts late
As evening approaches, a small gland in the brain begins to release melatonin, the hormone that signals to the body that night has arrived. Researchers time the start of this release using saliva samples taken in dim light.
- In children with ADHD, the release starts about 45 minutes late
- In adults with ADHD, it starts about 90 minutes late
Some studies found unusually high daytime melatonin in children with ADHD. It fell with methylphenidate, a common stimulant medication.
Cortisol normally peaks in the morning to help the body get going. In ADHD, it follows a flatter and later daily curve.
Even cells lining the inside of the cheek keep time. In people with ADHD, two genes at the core of the body’s clock switch on and off less strongly over the day. People with a weaker rhythm in one of those genes had more severe symptoms.
It is not clear which comes first. The authors noted that staying up late means more exposure to light at night, and that light could itself push these rhythms later.
Melatonin and light trials
In one trial of adults with ADHD, half a milligram of melatonin each night moved the start of their own melatonin release 88 minutes earlier, and their ADHD symptoms fell by 14%.
Children’s clocks responded too. In another trial, 101 children with ADHD and long-standing difficulty falling asleep took melatonin or a placebo nightly for four weeks.
- Melatonin moved their clocks 44 minutes earlier and added 20 minutes of sleep a night
- The clocks of children on the placebo moved 13 minutes later
However, the children’s behaviour and thinking scores did not change over those four weeks. When they later stopped taking melatonin, sleep moved later again in 92% of them.
Light has a similar effect. In a small pilot trial, adults with ADHD sat in front of a bright therapy lamp each morning for two weeks. The midpoint of their sleep moved 57 minutes earlier, and the further a person’s clock moved, the more their symptoms improved. Adults who received both light and melatonin had the biggest shift, of about two hours.
Routines helped children sleep
Some approaches need neither medication nor a lamp. In a 2015 trial of 244 children with ADHD, families met a psychologist or paediatrician twice, two weeks apart, to learn sleep strategies, followed by a phone call.
Six months later, the children had milder ADHD symptoms, better sleep, better behaviour and a better quality of life.
Stricter routines for night owls
A stricter routine has worked for night owls without ADHD. In one study, 22 healthy late sleepers got up two to three hours earlier, at the same time every day. They also:
- got morning light and cut evening light
- skipped late dinners
- avoided caffeine after 3pm
- exercised in the morning
Within three weeks, their clocks had shifted. Melatonin release started about two hours earlier, they woke 1.9 hours earlier, and their depression scores fell by about 58%.
Morning or evening exercise also appears to move the clock earlier in late sleepers. Neither approach has been tested in people with ADHD.
What the researchers recommend
Luu and Fabiano want doctors to start by asking people with ADHD about their sleep. Where someone shows signs of a delayed body clock, they suggest assessing their sleep patterns and, where possible, measuring melatonin release.
Treatment would then begin with habits:
- a fixed wake-up time
- bright light in the morning
- less light and screen time at night
- regular daily routines
Low-dose melatonin would be reserved for people whose melatonin release is known or likely to start late.
Questions that remain open
Some of the biggest questions are still unanswered. There is no evidence yet that treating the body clock alone makes ADHD go away. Researchers also do not know whether a late clock helps cause ADHD symptoms, or whether the symptoms push the clock later.
The authors are calling for trials that group people with ADHD by their body clocks. Such studies could show who responds to these treatments, and how long improvements in sleep take to show up in attention and behaviour.
With information from Earth.com
