By Maria Cohut

Researchers suggest that there may be a stronger link between ADHD and sleep problems than hitherto believed, and that the two may not be completely separate issues after all.

Data reported by the Centers for Disease Control and Prevention (CDC) indicate that approximately 11 percent of children aged 4 to 17 are diagnosed with attention deficit hyperactivity disorder (ADHD) in the United States.

Among the adult U.S. population, the National Institute of Mental Health report a 4.1 percent 12-month prevalence rate for the disorder.

ADHD is typically characterized by hyperactivity, a short attention span, and difficulties in self-organization. Sometimes, the disorder can be accompanied by one or several other conditions, including dyslexia, anxiety, and depression.

Another concern that has been flagged up in relation to ADHD is the existence of sleep problems, including sleep apnea and disturbed sleep patterns.

Mostly, ADHD and sleep disturbances have been treated as separate issues, but Prof. Sandra Kooij, from the VU University Medical Centre in Amsterdam, the Netherlands, believes that the two may be fundamentally interconnected.

Prof. Kooij explained for Medical News Today that, as a psychiatrist who specializes in ADHD, she has dealt with many cases in which the disorder seemed to be linked with sleep disturbances. This gave her the first impulse to look more closely into the connection.

She told us, "I am a psychiatrist specialized in adult ADHD since 1995, and from the beginning, the sleep problems that most people with ADHD suffer from intrigued me. Most of them had a similar pattern of late sleep onset, and difficulty getting up in the morning, leading to fatigue during daytime and role impairment."

"Sleep duration was usually short due to school or work obligations in the morning. This sleep loss seemed to increase the severity of ADHD symptoms as well," explained Prof. Kooij.

Most people with ADHD have sleep problems

Prof. Kooij and her colleagues have reviewed several studies that point to a link between sleep disturbances and ADHD, and they suggest that the evidence so far offers a strong basis for further evaluation.

"If you review the evidence, it looks more and more like ADHD and sleeplessness are two sides of the same physiological and mental coin," explains Prof. Kooij.

Prof. Kooij's investigation has revealed several interesting facts about the presence of sleep disturbances in individuals diagnosed with ADHD, and many of those have led her to form her hypothesis.

She notes, in the first place, that the majority of people diagnosed with ADHD also exhibit a disturbed sleep pattern. The physiological aspects of sleep are also affected which, in turn, could lead to other, more severe health implications.

"[W]e started to measure the onset of the sleep hormone melatonin in [the] saliva of people with ADHD with and without sleep onset problems. We found that late sleepers had their onset of melatonin 1.5 hours later than normal, correlating with the late sleep pattern," stated Prof. Kooij.

"[A]lso, their movement patterns and temperature during 24 hours were delayed," she added. "The next question was which other physical processes might be delayed, and what this would mean for their health in general."

People diagnosed with ADHD complain of a wealth of sleep disorders, such as:

restless legs syndrome, which is characterized by an urge to move one's legs during a state of rest, which disrupts normal sleep patterns

sleep apnea, in which abnormal - and disruptive - pauses in breathing occur during sleep

various circadian rhythm disturbances, referring to disruptions of the regular physiological cycle that naturally "times" sleep and wakefulness, including delayed sleep phase syndrome (DSPS)

DSPS is characterized by an impossibility to fall asleep before the small hours and increased difficulty in waking up in the morning.

Prof. Kooij told us that these disturbances can intensify the risk of other conditions, including obesity, hypertension, cardiovascular disease, diabetes, and cancer.

Some individuals with ADHD may therefore benefit from taking melatonin supplements, or from bright light therapy. Both approaches are recommended to people with sleep disorders but are also sometimes used to improve depression, especially in the case of seasonal affective disorder.

"We now aim to prevent this potential negative cascade of events for people with ADHD with lifetime sleep problems by advancing the late sleep phase using melatonin at night and/or light therapy in the morning, and measuring the effects on blood pressure, glucose levels, heart rate, and other biomarkers," stated Prof. Kooij

Photophobia, or oversensitivity to light, is also reported by 69 percent of adults diagnosed with ADHD. Prof. Kooij suggests that this oversensitivity leads them to wear sunglasses indiscriminately during the day, which, in turn, may increase the prevalence of sleep-related problems. She told us that she wondered whether "there is something going on in the eye that relates to ADHD and late sleep."

Prof. Kooij and her team are conducting research to find out which treatment may be most helpful in the case of sleep disorders. "[W]e try to find out if a low dose of melatonin (0.5 milligrams) in the evening is as good as higher dosages (3 milligrams), and which is best: melatonin, placebo, or melatonin plus light therapy in the morning," she said.

She also shared with us some tips for managing sleep disturbances, advising that people concerned about their sleep patterns should "stop using the light of screens after 10 p.m.," and that they should aim to "get up at the same time every morning, and if necessary, use a strong lamp to wake up [the] brain."

Where does the cause lie?

Should the link between ADHD and sleep disorders, Prof. Kooij is interested in finding out which way the causal relationship lies.

"If the connection is confirmed, it raises the intriguing question: does ADHD cause sleeplessness, or does sleeplessness cause ADHD? If the latter, then we may be able to treat some ADHD by non-pharmacological methods, such as changing light or sleep patterns, and prevent the negative impact of chronic sleep loss on health."

Prof. Sandra Kooij

She cautions that she and her colleagues do not suggest that disturbed sleep patterns are key to all ADHD diagnoses, but she still believes that the strong link requires more investigation.

"We don't say that all ADHD problems are associated with these circadian patterns, but it looks increasingly likely that this is an important element," she says.