CHICAGO (CBS St. Louis) – A new study sheds new light on losing weight…literally.

Researchers at Northwestern University found that people who were exposed to bright light in the morning had a significantly lower Body Mass Index (BMI) than those whose light exposure was later in the day.

“Light is a powerful biological signal and appropriate timing, intensity and duration of exposure may represent a potentially modifiable risk factor for the prevention and management of obesity in modern societies,” say study authors.

Participants in the study were asked to log their mealtimes and sleep times and were asked to wear a wrist device that monitored their movements.

Those who were exposed to daily light above 500 lux in the early part of the day had lower BMIs.

Room light is between 150-500 lux while outdoor light is more than 1,000 lux, even on cloudy days.

“The earlier this light exposure occurred during the day, the lower the individuals’ body mass index,” wrote co-lead author Dr. Kathryn Reid. “The later the hour of moderately bright light exposure, the higher a person’s BMI.”

The influence of morning light exposure on body weight was independent of other factors, like the level of physical activity, calorie intake, amount of sleep or age.

The study authors concluded that light exposure accounted for about 20 percent of an individual’s BMI.

“Our results suggest that the relationship between light and BMI is not simply a function of the accumulated minutes of light during the day, but more importantly the temporal pattern of light exposure above a biological threshold.”

Senior author Dr. Phyllis Zee wrote that most Americans do not get enough natural light in the morning because most of us spend much of our days indoors. “Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance.”

20 to 30 minutes of morning light is enough to lower BMI. “The message is that you should get more bright light between 8 a.m. and noon,” said Zee.

(TM and © Copyright 2014 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2014 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)

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