Evening Screen Exposure and Circadian Rhythms: Investigating Salivary Melatonin Suppression and Actigraphy-Based Sleep Patterns in 15- to 24-Month-Old Toddlers

Abstract

Studies suggest that pre-bedtime screen exposure disrupts the circadian rhythm by suppressing melatonin release in the pineal gland. This study investigates melatonin suppression in toddlers after screen exposure in the home environment. We hypothesized that viewing a video as opposed to viewing a picture book before bedtime would suppress melatonin release and disrupt subsequent sleep. Thirty-two toddlers aged 15 to 24 months participated in a within-subject design. On 2 consecutive evenings, caregivers exposed their toddler for 15 minutes to either a video on a touchscreen with the blue light filter deactivated or to a picture book, starting 45 minutes pre-bedtime. To determine melatonin concentration, caregivers collected 1 saliva sample before exposure (baseline) and 2 saliva samples 5 minutes (post_1) and 20 minutes (post_2) after exposure. Toddlers’ sleep–wake patterns were monitored using actigraphy. Multilevel models revealed that salivary melatonin increased from baseline to post_2 irrespective of touchscreen or picture book exposure. Changes in melatonin concentration from baseline to post-exposure measurement and sleep behavior did not differ as a function of exposure condition. Sleep behavior was unrelated to melatonin suppression scores. Contrary to expectations, our results suggest that viewing a 15-minute video on a touchscreen within an hour of bedtime is insufficient to suppress evening melatonin release and disrupt sleep under these experimental conditions in German toddlers. More studies with toddlers under naturalistic conditions are needed to understand the relevance of screen light-induced melatonin suppression as a mechanism to explain relationships between screen exposure and sleep health.