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Dim Light At Night Could Cause Weight Gain! Obesity epidemic has been a great concern for many countries around the world, especially those in the West. This is because the health care cost to deal with the consequence of obesity epidemic is rather huge. People who are overweight or obese are at a higher risk of getting chronic diseases including Type-2 diabetes, hypertension (high blood pressure), stroke and heart disease. For decades, sedentary lifestyle and unhealthy diet have been accused of causing overweight and obesity. Recently, a study on mice provided a new discovery on obesity: too much light at night might lead to weight gain. Researchers from Ohio State University found that mice exposed to a dim light at night over 8 weeks had a weight gain of about 50 percent more than those mice that lived in a standard light-dark cycle. There were no differences in activity levels or daily consumption of food for both groups of mice. Published in the ‘Proceedings of the National Academy of Sciences’ journal, the study reported that light appeared to have an effect on the metabolism that causes weight gain. There could be something regarding the light at night that had made the mice in the study want to eat at the wrong times to properly metabolize their food. Such results, if confirmed in humans, would suggest that late-night eating might lead to obesity.
In the study, mice were placed in one of the 3 lighting conditions. One group of mice were exposed to 24 hours of constant lighting, the other group was placed under a standard light-dark cycle including 16 hours of light and 8 hours of darkness, and the last group were housed under 16 hours of daylight and 8 hours of dim light. Compared with mice in the standard light-dark cycle, those in dim light at night had significantly higher increases in body mass, beginning in the first week of and throughout the study. At the end of the study, mice housed under dim-light-at-night condition had gained about 12 grams of body mass, comparing to 8 grams for those in the standard light-dark cycle. For mice in constant bright light, weight gain was also more than those in the standard light-dark cycle. However, the mice exposed to dim light were a more important comparison for humans. While mice that were exposed to dim light did not really eat more than others, they consumed more food at night. Realizing the timing of eating was important, researchers carried out a second study but with slight changes. Instead of having food available at all times, food was restricted to either the times when mice would normally be active or when they would normally be at rest. Results from this study showed that mice exposed to dim light at night did not have a greater gain in body mass than others when their food was restricted to times when they normally would be active. Overall, the finding supports the fact that timing of eating is critical to weight gain and also provides clues for causes of the obesity epidemic in the Western countries. Light at night is an environmental factor that might be contributing to the obesity epidemic in ways that people do not expect. The study, however, did not find significantly different levels of corticosterone in mice living in dim light and those living in a standard light-dark cycle. This indicates that changes in metabolism in the mice do not have to be triggered by changes in levels of corticosterone, a stress hormone that has been associated with changes in metabolism. It is the belief of researchers that the light could disrupt levels of hormone melatonin that is involved in metabolism. Furthermore, the lighting might affect the expression of clock genes, which help control when animals feed and when they are active. Late-night eating could be a particular risk factor for obesity if these results could be confirmed in humans. While maintaining body weight requires keeping caloric intake low and physical activity high, late-night eating might explain why some people who maintain good energy balance still gain weight.
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