October 11, 2010
Researchers from Israel and the USA believe they have found evidence that demonstrates a link between obesity and metabolic disorders and exposure to LAN (light at night) in animal studies. In an article published in Proceedings of the National Academy of Sciences they found that mice exposed to dim light during their sleeping hours for a period of eight weeks had a 50% higher weight gain compared to mice that slept in the dark. Even reducing their food intake and making them do more exercise did not bring their weight down to that of the other mice that slept in the dark, unless they made sure the availability of food matched a mouse’s natural eating times.
The investigators, from the Departments of Neuroscience and Psychology, Ohio State University, Columbus, Ohio, and the Israeli Center for Interdisciplinary Research in Chronobiology, University of Haifa, explain as background information that the steady rise in the rates of obesity and metabolic disorders among humans have coincided with an increase in LAN and shirt work.
The 24-hour rhythm that regulates the state of our internal energy levels and metabolism is controlled by an internal biological clock that works in parallel with and responds to light information, the authors wrote. Our internal body clock (“circadian clock”) prepares us for predictable events, such as the availability of food and sleep. When the function of this clock is disturbed, our bodies experience a disruption in our metabolism and body-rhythms (circadian cycle).
Put simply – the predictability of light and day regulates our body clock, which regulates our metabolism. When the light and dark cycle is disrupted, so is our body metabolism, and also when we decide to eat.
The investigators assessed the effects of LAN on the BMI (body mass index) of male mice to see whether there might be a casual relationship between exposure to light during the night and obesity.
They found that mice exposed to light at night had considerably higher BMIs and lower glucose tolerance compared to mice kept in a normal day/night cycle (dark at night). The difference in BMI persisted even after their calorie intakes and total daily physical activity were altered.