Attention Deficit Hyperactivity Disorder (ADHD), which is associated with many sleep-related disorders, including restless-leg syndrome, sleep apnea, circadian rhythm disturbance and delayed sleep phase syndrome, was until now thought to be separate issues.
"There is extensive research showing that people with ADHD also tend to exhibit sleep problems," said Sandra Kooij, Associate Professor at VU University Medical Centre in Netherlands.
However, "based on existing evidence, it looks very much like ADHD and circadian problems are intertwined in the majority of patients", Kooij added.
According to the findings proposed at the 30th ECNP Congress in Paris, the association is because the day and night rhythm is disturbed, the timing of several physical processes is disturbed, not only of sleep, but also of temperature, movement patterns, timing of meals.
"If you review the evidence, it looks more and more like ADHD and sleeplessness are two sides of the same physiological and mental coin," Kooij said.
In 75 per cent of ADHD patients, the physiological sleep phase -- where people show the physiological signs associated with sleep such as changes in the level of the sleep hormone melatonin and changes in sleep-related movement -- is delayed by 1.5 hours.
Many sufferers benefit from taking melatonin in the evening or bright light therapy in the morning, which can help reset the circadian rhythm, Kooij explained.
Researchers are working to confirm this physical-mental relationship by finding biomarkers such as Vitamin D levels, blood glucose, cortisol levels, 24 hour blood pressure and heart rate variability, which may help "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", Kooij said.
"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," Kooij noted.