There is no conflict of interest.
Highlights
- The study’s objective was to examine the impact of bright light exposure treatment on health outcomes.
- The study used a randomized controlled trial that assigned adults into a bright light treatment group or a control group. The primary data source was a circadian phase assessment. The authors used statistical models to compare the outcomes between treatment and control group members.
- The study found a significant relationship between bright light exposure during the night shift and higher overlap between melatonin secretion and scheduled sleep.
- This study receives a low evidence rating. This means we are not confident that the estimated effects are attributable to bright light exposure treatment; other factors are likely to have contributed.
Intervention Examined
Features of the Study
The study was a randomized controlled trial conducted at a laboratory in Boston, Massachusetts. The goal of the bright light exposure treatment was to time the light exposure correctly to help the body adjust to night shift work hours. Participants followed a schedule that simulated a counterclockwise shift of five 8-hour workdays followed by two days off. During their shifts, they worked on a computer task where the light exposure was increased at intervals. After their 8-hour shift, they could go home and sleep for 8 hours according to a sleep schedule aligned with their work hours.
The authors randomly assigned 29 non-shift working adults into a treatment or control group. The sample included 15 women and 14 men with an average age of 27.7 years. All participants were healthy, did not take any medication, and avoided alcohol and caffeine during the study. The treatment group received intermittent bright light exposure during their workday, while the control group experienced normal light levels. The primary data source was a circadian phase assessment conducted weekly at the end of each shift rotation to evaluate the timing of melatonin secretion in relation to their work and sleep schedules. The authors used statistical models to compare the differences in outcomes between treatment and control group members.
Findings
Health and safety
- The study found a significant relationship between bright light exposure and hours of overlap between melatonin secretion and the sleep schedule during the night shift. However, the study did not find a significant relationship during the evening or day shifts.
Considerations for Interpreting the Findings
Although the study was a randomized controlled trial, the study had high attrition. Also, the authors did not account for preexisting differences between the groups in group composition by race/ethnicity or control for the differences in their analyses as required by the protocol. These preexisting differences between the groups—and not the bright light exposure treatment—could explain the observed differences in outcomes. Therefore, this study is not eligible for a high or moderate causal evidence rating.
Causal Evidence Rating
Research Guidelines
Review Protocol: Living Systematic Annual Search and Review Protocol
Review Guidelines: Causal Evidence Guidelines