Light Exposure Timing Influences Metabolism

A randomized, controlled, crossover trial in overweight insulin-resistant volunteers in the Netherlands suggested that in contrast to Dim day–Bright evening condition, Bright day–Dim evening condition mostly elicited favorable metabolic outcomes. The trial included 14 overweight 40–75 years male and female, insulin-resistant volunteers between July 2018 and November 2019. Participants were randomly allocated to two 40 h laboratory sessions with different 24 h lighting protocols while staying in a metabolic chamber under real-life conditions: electric bright light (~1250 lx) during the daytime (08:00–18:00 h) and to dim light (~5 lx) during the evening (18:00–23:00 h) in the Bright day–Dim evening condition, or vice versa in the Dim day–Bright evening condition. Spending the day in bright light resulted in a greater increase in postprandial triacylglycerol levels following breakfast, but lower glucose levels preceding the dinner meal at 18:00 h, compared with dim light (5.0 ± 0.2 vs 5.2 ± 0.2 mmol/l). Dim day–Bright evening reduced the increase in postprandial glucose after dinner compared with Bright day–Dim evening (incremental AUC: 307 ± 55 vs 394 ± 66 mmol/l × min). After the Bright day–Dim evening condition the sleeping metabolic rate was identical compared with the baseline night, whereas it dropped after Dim day–Bright evening. Melatonin secretion in the evening was strongly suppressed for Dim day–Bright evening but not for Bright day–Dim evening. Distal skin temperature for Bright day–Dim evening was lower at 18:00 h (28.8 ± 0.3°C vs 29.9 ± 0.4°C) and higher at 23:00 h compared with Dim day–Bright evening (30.1 ± 0.3°C vs 28.8 ± 0.3°C). Fasting and postprandial plasma insulin levels and the respiratory exchange ratio were not different between the two lighting protocols at any time. The findings are in line with some previous studies and suggest that optimizing indoor light conditions to more closely mimic the natural light/dark cycle holds promise to prevent adverse effects on metabolism associated with the nowadays prevailing constant indoor lighting conditions. Source: https://link.springer.com/