Diurnal Light Exposure and Rest-Activity Rhythms in Relation to MASLD: Insights From 2 Nationwide Cohort Studies

CONTEXT: Circadian rhythms may influence metabolic dysfunction-associated steatotic liver disease (MASLD), but the effect of personal light exposure and rest-activity rhythms on MASLD risk remain unclear. OBJECTIVE: To examine the associations between 24-hour light exposure, rest-activity rhythm (24-h-RAR), and the risk of incident MASLD, as well as how these factors influence genetic risk and life expectancy in individuals with MASLD. METHODS: This study used accelerometry data from both the National Health and Nutrition Examination Survey (NHANES) and UK Biobank cohorts. 24 h-RAR was assessed using nonparametric metrics, including activity level during the most active 10 hours (M10), activity level during the least active 5 hours (L5), relative amplitude (RA), M10 onset, and L5 onset. Light exposure was categorized into daytime and nighttime periods, with exposure durations recorded separately at different threshold levels. The primary outcome was MASLD, with secondary outcomes including fibrosis and cirrhosis. RESULTS: In the UK Biobank prospective analysis, each 0.1-unit and 1-unit increase in RA and M10 were associated with a 30% and 2% reduction of MASLD risk, respectively. In contrast, each 1-unit increase in L5 and delayed L5 onset were linked to an 8% and 21% increase of MASLD risk. Moreover, each additional hour of daylight exposure above 6000 lux was associated with a 9% lower risk of MASLD, while each additional 30 minutes of nocturnal light exposure above 30 lux corresponded to a 22% higher risk of MASLD. Additionally, a favorable 24 h-RAR profile and adequate light exposure were associated with a lower risk of fibrosis and cirrhosis, as well as improved life expectancy among participants with MASLD. Similar associations were observed in the NHANES analysis. CONCLUSION: Greater daytime light exposure, reduced nocturnal light exposure, and regulated RARs may protect against MASLD and prevent its progression to liver fibrosis and advanced liver disease.