COPENHAGEN, Denmark — Most people assume it’s naturally easier to keep up with healthy routines during the summer. After all, the Sun is shining and the days are longer. Interestingly, new research actually suggests the winter months may promote healthier eating habits. Scientists at the University of Copenhagen explain that the amount of natural light exposure people get on a daily basis influences both how they eat and expend energy. This latest work also shows that eating habits in winter may be better for metabolic health than eating habits during the summer.
Importantly, this project only involved mice. Researchers examined the metabolism and weight of mice exposed to both winter light and summer light.
“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 carried out the research while a postdoc at Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen, in a media release.
“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 a 24-hour period. And this then led to benefits in metabolic health.”
This project was the first of its kind to examine light hour’s influence on metabolism in mice, which are not considered seasonal animals (just like humans) as they do not only breed during specific seasons. Animals that do breed during specific seasons usually gain weight before their breeding season to help save energy supplies.
The research team was inspired to conduct this research by significant variations in daylight hours seen across various regions of the world.
“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,” Small explains.
Consequently, study authors set out to determine what these seasonal light differences meant for the metabolism. While this research focused on mice, the findings may one day prove relevant for humans as well. Most people in the world live with at least a two-hour difference 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,” Small says. “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.”
Since the study was conducted using mice as the experimental subjects, researchers cannot say with any confidence that the same goes for humans at this point.
“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.
Small adds that this new knowledge is key to cultivating a better understanding of how eating patterns are affected by light and seasons, which may one day help humanity understand why certain people gain more weight, or if people tend to gain more weight during specific times of the year.
“Differences in light between summer and winter could affect our hunger pathways and when we get hungry during the day,” Small concludes.
The study is published in the journal Cell Metabolism.
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