07/04/2014 09:35 BST | Updated 07/04/2014 09:59 BST

Is Bright Light The Key To Losing Weight? New Study Links Exposure To Lower BMI

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Although BMI (Body Mass Index) has come under scrutiny as to whether it is an accurate measurement of healthy weight, a new study has shown how your exposure to light (from the sun, not a bulb) affects it.

The length of exposure is important, but so is the time of day during which you clock your hours of sunlight.

"People who had most of their daily exposure to even moderately bright light in the morning had a significantly lower body mass index (BMI) than those who had most of their light exposure later in the day," reported North Western University, where the study was conducted.


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The authors, who came from the Feinberg School of Medicine in Chicago found "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," said The Independent.

BMI is a ratio calculated from a person's weight and height.

“Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance,” said study senior author Phyllis C. Zee, M.D. “The message is that you should get more bright light between 8 a.m. and noon.” About 20 to 30 minutes of morning light is enough to affect BMI.

Zee is the Benjamin and Virginia T. Boshes Professor of Neurology and director of the Northwestern Medicine Sleep and Circadian Rhythms Research Program at Northwestern University Feinberg School of Medicine. She also is a neurologist at Northwestern Memorial Hospital.

“If a person doesn’t get sufficient light at the appropriate time of day, it could de-synchronise your internal body clock, which is known to alter metabolism and can lead to weight gain,” Zee said. The exact mechanism of how light affects body fat requires further research, she noted.

If that isn't motivation enough to walk to work or take regular breaks outdoors, we don't know what is.

The study was published April 2 in the journal PLOS ONE.