Attention-deficit-hyperactivity-disorder (ADHD) is a frequent psychiatric disorder present in childhood, where sleep-problems are a prominent, pervasive and clinically important feature. However, our understanding of whether sleep-problems mimic or exacerbate daytime ADHD-symptom expression remains insufficient.

Research examining sleep and daily activity in toddlers with early signs of ADHD might help identify early risk factors.

To investigate whether disturbed sleep patterns and daily activity level is associated with early signs of ADHD in toddlers.

Twenty-four toddlers from the Danish Odense Child Cohort scoring above the 93rd percentile on the ADHD scale of the Child Behaviour Checklist for ages 1½–5 were categorized as cases and compared to 25 age and gender-matched controls scoring below the 50th percentile. Daytime and nocturnal activity for 49 toddlers were assessed through seven days of actigraphy. Parents completed Children's Sleep Habits Questionnaire (CSHQ) and the ADHD Rating Scale IV Preschool Version (ADHD-RS).

Actigraphic data revealed an increased night-to-night variability, prolonged total sleep time, fewer sleep interruptions and fewer minutes in moderate-to-vigorous-physical activity (MVPA) in cases compared to controls. Increased night-to-night variability was found significantly associated with higher total scores on both the CSHQ and ADHD-RS. Further, fewer minutes in MVPA were associated with a higher parent-reported motor activity on the ADHD-RS.

Findings show that early signs of ADHD are associated with irregular sleep patterns and lower daytime activity, as illustrated by actigraphy. Studies investigating early ADHD risk factors could lead to a preschool ADHD risk index to help guide future early intervention.

The authors have not supplied their declaration of competing interest.