Endocrine Abstracts

Introduction: Adolescents spend much time using blue-light emitting screen devices such as smartphones, tablets and computers. Blue light affects the central circadian clock in the suprachiasmatic nucleus (SCN) as well as melatonin secretion by the pineal gland. Screen use in adolescents strongly associates with reduced sleep quality and sleep duration. However, there is a lack of intervention studies that reduce blue light exposure due to screen use in adolescents.

Methods: We identified frequent screen users (use ≥ 4 hr per day, n=25) and infrequent screen users (use ≤1 hr per day, n=30) among Dutch adolescents aged 12–17 yr. In a 5-week randomized controlled crossover trial, the frequent screen users were assessed for 3 evening interventions of 1 week each, with 1-week washout periods: 1) during habitual screen use; 2) while wearing blue-light-blocking glasses; 3) while completely refraining from screen use. In a case-control sub-study, infrequent screen users were assessed for 1 week. In every measurement week, sleep was assessed using sleep diaries and actigraphy, and melatonin onset was assessed using at home 30-minute saliva sampling on the final evening of each intervention week. The trials were registered as NTR6712 (RCT) and NTR6722 (case-control).

Results: In frequent screen users, blue-light-blocking glasses as well as refraining from screen use induced an earlier mid-point of sleep compared to habitual screen use. Both interventions restored sleep times of frequent users to around those of infrequent users. In many subjects it was difficult to identify a clear-cut melatonin onset, but blue-light-blocking glasses reduced absolute melatonin levels compared to habitual screen use.

Conclusion: This is the first randomized controlled study in a real life setting showing that, among frequent screen using adolescents, blue-light-blocking glasses as well as abstinence of screen use restores their late sleep towards the earlier timing seen in infrequent screen users. These effects may be partly mediated via reduced melatonin suppression by blue light.