Working with mice, Small and teammates have established links between seasonal light exposure and metabolism that might ultimately be extended to humans. They report that “Except for latitudes close to the equator, seasonal variation in light hours can change dramatically between summer and winter. . . . We hypothesized that altering the seasonal photoperiod affects both the rhythmicity of peripheral tissue clocks and energy homeostasis. Mice were housed at photoperiods representing either light hours in summer, winter, or the equinox. Mice housed at a winter photoperiod exhibited an increase in the amplitude of rhythmic lipid metabolism and a modest reduction in fat mass and liver triglyceride content. Comparing melatonin-proficient and -deficient mice, the effect of seasonal light on energy metabolism was largely driven by differences in the rhythmicity of food intake and not melatonin. Together, these data indicate that seasonal light impacts energy metabolism by modulating the timing of eating.” So, the number of hours of light exposure that mice have at different seasons influences how they eat and burn energy.
Lewin Small, Leonidas Lundell, Jo Iverson, Amy Ehrlich, Morten Dall, Astrid Basse, Emilie Dalbram, Ann Hansen, Jonas Treeback, Romain Barres, and Juleen Zierath. 2023. “Seasonal Light Hours Modulate Peripheral Clocks and Energy Metabolism in Mice.” Cell Metabolism, vol. 35, no. 10, pp. 1722-1735, https://doi.org/10.1016/j.cmet.2023.08.005