Researchers at Northwestern University's Feinberg School of Medicine in Chicago have found that exposure to bright light in the morning is linked to a significantly lower BMI.
The earlier participants saw daylight, the lower their body mass index. Conversely, those who weren't exposed to bright light until later in the day were significantly heavier in relationship to their height. This effect was independent of the number of hours’ sleep participants were getting. Most interestingly, the study showed that morning light lowers our BMI independently of how many calories we eat or how much exercise we're getting. It appears that the time we start our day directly affects our metabolic rate, accounting for an impressive 20 percent of our BMI score.
“Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance,” explained Phyllis C. Zee, M.D., director of the Sleep and Circadian Rhythms Research Program at Northwestern. “If a person doesn’t get sufficient light at the appropriate time of day, it could de-synchronize your internal body clock, which is known to alter metabolism and can lead to weight gain.”
According to Zee, the crucial hours we should be aiming to see bright light are between eight 8am and midday. No need to overdo it though; about 20 to 30 minutes of this early light is enough to affect BMI.
It isn’t just people who get up late who are at risk of upsetting their metabolism. The fact that most of us work indoors in poorly lit environments also contributes to the problem. The results of the study showed 500 lux to be "the magic number" in lowering BMI. This is about 200 to 300 lux higher than the artificial lighting provided in an average office.
The researchers believe that their findings could lead to a break-through in approaches to weight management, with the manipulation of light providing a whole new avenue in the treatment of obesity. In addition, lifestyle changes such as taking lunch breaks outside (weather permitting), could help get society in shape. Zee suggests that we should cultivate a good relationship with our body clocks from a young age, and is convinced that improved lighting and outdoor breaks in schools could “prevent obesity on a larger scale”.