“We found that even in non-seasonal animals, differences in light hours between summer and winter do cause differences in energy metabolism. In this case, body weight, fat mass and liver fat content,” says Lewin Small, who researched while a postdoc at Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen. He adds, “We found this mostly in mice exposed to winter light hours. These mice had less body weight gain and adiposity. They have more rhythmicity in the way they eat over 24 hours. And this then led to benefits in metabolic health.”
The study is the first of its type to investigate the effect of light hours on metabolism in mice, which are not considered seasonal animals because, like humans, they do not exclusively breed during certain seasons. Animals that reproduce at specified times build weight before the breeding season to conserve energy supplies.
Metabolism is Affected by Daylight Hours
The researcher was inspired to start the study because of the substantial diversity in daylight hours around the globe.
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“We study the influence of the time of day on aspects of metabolism such as exercise, obesity and diabetes. However, most studies that investigate this link do so assuming an equal length of day and night all year round,” says Lewin Small.
As a result, they wanted to know what seasonal light changes meant for metabolism. Most people on the planet experience a two-hour variation in light between summer and winter.
“I come from Australia, and when I first moved to Denmark, I was not used to the huge difference in light between summer and winter and I was interested in how this might affect both circadian rhythms and metabolism,” says Lewin Small and adds, “Therefore, we exposed laboratory mice to different light hours representing different seasons and measured markers of metabolic health and the circadian rhythms of these animals.”
Because the study used mice as the experimental participants, it is not possible to assume that the same holds for humans.
“This is a proof of principle. Do differences in light hours affect energy metabolism? Yes, it does. Further studies in humans may find that altering our exposure to artificial light at night or natural light exposure over the year could be used to improve our metabolic health,” says Juleen Zierath, Professor at the Novo Nordisk Center for Basic Metabolism Research (CBMR) and senior author of the study.
Lewin Small adds that the new knowledge is crucial for understanding how light and seasons affect eating behaviors, which may help us understand why some people gain more weight or if people gain more weight at certain times of the year.
“Differences in light between summer and winter could affect our hunger pathways and when we get hungry during the day,” he says.
References:
- https:doi.org/10.1016/j.cmet.2023.08.005
Source: Medindia
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