A Good Dose Of Morning Sunlight Keeps Off The Pounds: Study
April 3, 2014

A Good Dose Of Morning Sunlight Keeps Off The Pounds: Study

Brett Smith for redOrbit.com - Your Universe Online

By most accounts, a healthy lifestyle should include a balanced diet, regular exercise, and – according to a new study published in the journal PLOS ONE – a long dose of bright light in the morning.

In the study, researchers from Northwestern University found that the time, strength and duration of light exposure is directly linked to body mass index (BMI), even after considering confounding factors.

"The earlier this light exposure occurred during the day, the lower individuals' body mass index," said study author Kathryn Reid, professor of neurology at Northwestern University. "The later the hour of moderately bright light exposure, the higher a person's BMI."

Light exposure accounted for approximately 20 percent of a person's BMI. The impact of morning light exposure was found to be separate from a person's physical activity level, caloric consumption, sleep habits, age or time of year.

"Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance," said senior author Dr. Phyllis C. Zee, a professor of neurology at Northwestern University. "The message is that you should get more bright light between 8 a.m. and noon."

"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," she added.

According to the study team, the predominantly indoor lifestyle of the typical American means they do not get enough normal light in the morning to have a decreasing influence on BMI, which they said was between 20 and 30 minutes of exposure. Americans also work in poorly lit environments, usually about 200 to 300 lux – much less than "the magic number" of 500 lux discovered to lower BMI in the study. On a cloudy day, outdoor light is greater than 1,000 lux. The study team said it is difficult to achieve even this level of light intensity with typical indoor lighting.

"Light is a modifiable factor with the potential to be used in weight management programs," Reid said. "Just like people are trying to get more sleep to help them lose weight, perhaps manipulating light is another way to lose weight."

For the study, the team recruited 54 volunteers with an average age of 30 years old. Participants wore a wrist actigraphy monitor that assessed their light exposure and sleeping patterns for a week in normal-living situations. Their calorie consumption was recorded for a week through the use of food diaries.

Zee said the study’s findings reinforce the importance that circadian rhythm plays in maintaining a healthy body.

"We focus on how too much light at night is bad; it's also bad not to get enough light at the appropriate time during the day," she said.

The neurology professor added that the exact mechanism behind this effect is unknown, however, in the mean time – people should be encouraged to get more exposure to light during the course of their day, such as installing more windows or taking more breaks outside.

"This is something we could institute early on in our schools to prevent obesity on a larger scale," Zee said.