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, the study has found.
The timing, intensity and duration of your light exposure during the day is linked to your weight.
“The earlier this light exposure occurred during the day, the lower individuals’ body mass index,” said Kathryn Reid, a research associate professor of neurology at Northwestern University’s Feinberg School of Medicine.
The later the hour of moderately bright light exposure, the higher a person’s BMI, he added.
The influence of morning light exposure on body weight was independent of an individual’s physical activity level, caloric intake, sleep timing, age or season.
It accounted for about 20 percent of a person’s BMI.
“Light is the most potent agent to synchronise your internal body clock that regulates circadian rhythms, which, in turn, also regulate energy balance,” senior author Phyllis C. Zee explained.
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.
“If a person does not 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 added.
Just like people are trying to get more sleep to help them lose weight, perhaps manipulating light is another way to lose weight, said the study published in the journal PLOS ONE.