Exposure to bright light at night reduces melatonin production by 63% and reduces fat oxidation (during bright light exposure & sleep).

(Choi et al., 2022)

Our lives continue to get busier, and we work longer hours than ever. Chronic exposure to artificial light at night has been associated with higher body weight and a higher risk of obesity.

Choi et al., 2022, a randomized controlled crossover trial investigated the effect of exposure to light at night on energy metabolism. Two groups were assigned in random order to bright light (10,000 lux), or dim light (<50 lux) between 9.00 pm to 12.00 am. Later crossed over to the other condition after at least seven days. They slept in a metabolic chamber between 12 to 7 am.

Melatonin level was 63% lower in people exposed to bright light than dim light. The bright light group also experienced a decrease in fat oxidation (during light exposure and sleep) and an increase in carbohydrate oxidation during sleep.

This raises the question, does exposure to bright light later at night disrupt circadian rhythm and leading to changes in metabolism.

Authors’ conclusion – chronic bright light exposure at night may lead to obesity risk due to disturbances in circadian rhythms and macronutrient metabolism.

Reference:

Choi Y, Nakamura Y, Akazawa N, Park I, Kwak HB, Tokuyama K, Maeda S. Effects of nocturnal light exposure on circadian rhythm and energy metabolism in healthy adults: A randomized crossover trial. Chronobiol Int. 2022 Apr