Scientists untangle the complicated link between ADHD and sleep

Scientists don’t know the exact cause of attention-deficit/hyperactivity disorder, or ADHD. Genes may play a role but can’t quite explain its prevalence. In the United States, an estimated 8.4 percent of children and 2.5 percent of adults have the mental health disorder. Many more — how many aren't known — live with ADHD traits, struggling with tendencies like inattention and impulsiveness, but not to the degree of a diagnosis.

As the CDC puts it, “there are many unanswered questions about ADHD.” However, one question scientists are edging toward answering is the question of ADHD and sleep. Research suggests for many people with ADHD, sleep may very well be the Alpha and the Omega — a hurdle associated with a circadian rhythm that differs from the norm and exacerbated by sleepless nights.

ADHD and sleep loss have a relationship of mutual reinforcement, explains Dr. Sandra Kooij, a professor at the Amsterdam University Medical Center and a specialist in adult ADHD. Circadian rhythm is delayed in approximately 80 percent of people with ADHD, she tells me. This is associated with later onset of the sleep hormone melatonin. In the average population, this onset happens at about 9:30 p.m. In people with ADHD, it happens around 11 p.m.

This may explain why people with ADHD so often sleep late, Kooij explains — often later than they actually want, and later than they should for their health. Many sleep disorders, in turn, are more frequent among people with ADHD compared to the general population with afflictions like restless leg syndrome, sleep apnea, and insomnia. And what trails behind a sleep disorder is sleep loss.

“ADHD and sleep loss usually come together and reinforce each other’s severity,” Kooij says. “Sleep loss has consequences that look like ADHD symptoms: lack of concentration, worse memory, irritability, craving for carbohydrates, and obesity.”

Recent research suggests individuals with high ADHD traits are also especially vulnerable to the negative effects of sleeplessness. A study published in Biological Psychiatry included 180 adult participants without an ADHD diagnosis, who were split into a group that was allowed to either have a night of normal sleep or no sleep at all. The next day, they were subsequently tested on measures of emotional control and executive control; executive functions are the mental processes that allow one to concentrate, exhibit self-control, and meet unanticipated challenges.

"ADHD and sleep loss usually come together and reinforce each other’s severity."

The goal of the study, co-author Dr. Predrag Petrovic tells me, was to answer two questions. First was the question of why some people are much more affected by sleep loss than others. The second was “to understand how top-down regulation works in the brain and what happens when it does not work properly.

Petrovic, a lecturer and senior physician at the Karolinska Institutet in Sweden, explains that ADHD is a typical example of dysfunctional top-down regulation. This has to do with the way the brain regulates functions. Bottom-up emotions are immediate responses, while top-down emotions are more of a conscious response. Executive functions, in turn, are a family of top-down mental processes.

The study revealed, overall, the sleep-deprived group performed worse on those tests, and people with high ADHD traits especially so. So, for example, if an individual who has problems with emotional instability on average did not sleep, they especially struggled with cognitive tasks that involve emotional regulation.

Why does this happen? Exhibiting high ADHD traits means one has an issue with regulating factors like inattention and inhibition. There’s a normal distribution of these symptoms across the population, but in order to have an ADHD diagnosis, you need “functional loss that is significant,” Petrovic explains. That doesn’t mean that the symptoms can’t cause you problems, but it does mean you’re not prohibited from having a “normal life.”

However, there is some evidence here that sleeplessness can tip the scale, and too little sleep could eventually result in a clinical situation.

“In this case, it is possible that you would not be classified as a patient when you have a normal sleep, but classify as a patient if you have a lack of sleep,” Petrovic says.

Why this is, he explains, basically comes down to having “less buffer capacity.” They are having to recover, already being a few steps back.

“Our hypothesis was that if you already have some suboptimal function in top-down regulation, you will also be more vulnerable to extreme situations for the brain after not sleeping,” Petrovic explains.

The real mystery, Kooij says, is whether these issues of sleep and ADHD occur because they both stem from the same biological question.

“Is ADHD in fact a sleep disorder? Or is the biological clock behind both problems?” she asks.

Knowing will take more research, although it’s known that the circadian rhythm change is a heritable trait. Time is pressing. Because these sleep patterns are seen across a lifetime, they can cause a lifetime of health consequences ranging from obesity due to sleep loss to chronic diseases like hypertension and cardiovascular disease.

“ADHD people happen to be physically jet-lagged due to the late sleep pattern, and I think this may be related to the many physical complaints they have,” Kooij says.

Is there a fix? People with ADHD or ADHD traits who struggle with sleep should consider two possible solutions: good sleep hygiene and chronotherapy.

Chronotherapy, Kooij explains, involves taking melatonin in the evening and bright light therapy in the morning. The timing of this matters, as does the timing of good sleep hygiene. It’s not only sleeping seven to eight hours and not much more, she says. It’s also about sleeping in the right time phase — between 11 p.m. and 7 a.m.

Sleep hygiene also involves limiting the use of light and screens at night.

“Throw out your smartphone and computer from the bedroom and get an old-fashioned alarm clock,” Petrovic says. “Don’t use smartphones and computers one to two hours before you go to bed.”