Light therapy for the treatment of delayed sleep-wake phase disorder in adults: a systematic review

Delayed sleep-wake phase disorder (DSWPD) is characterized by sleep onset times, beyond the usual schedules and social conveniences, which potentially impacts on health as well as on school and professional performance. The most common treatment for DSWPD is the light administration (light therapy), through light devices, with or without behavioral instructions. Since there is no consensus in the literature about its efficacy and how it should be processed, this study aims to evaluate the light therapy effectiveness in the delayed sleep-wake phase disorder therapeutics. A systematic review was conducted using the MEDLINE/PubMed, Virtual Health Library Brazil, PsycINFO, Web of Science and Scopus databases along with a hand search until September 2020. The included studies presented participants diagnosed with insomnia or DSWPD, over 18-years old, treated only with morning light therapy, mentioning the light intensity (lux) used, and investigations with a control group. Studies reporting individuals with neurological or psychiatric disorders, shift-workers, or evaluating other sleep disorders were excluded. Among the 411 studies identified, five were selected for this review, resulting in a total sample of 140 individuals. Only two studies produced long-term results, showing that the benefits did not persist. In most studies, there were no statistically significant differences in the variables when comparing the intervention group and the control group. However, there were substantial clinical and laboratory advances in the sleep phase using light therapy when comparing phase advances for the same group concerning baseline values of sleep variables.