Skip to content
My WebMD Sign In, Sign Up

Fitness & Exercise

Font Size

The Morning Light May Help You Stay Slim

Study found people tended to be leaner if they got sun exposure earlier, rather than later, in day

WebMD News from HealthDay

By Serena Gordon

HealthDay Reporter

WEDNESDAY, April 2, 2014 (HealthDay News) -- Spending time in the bright morning light may help you slim down, new research suggests.

The small study found that people exposed to more light earlier, rather than later, in the day tended to be leaner than their peers.

"We were very interested in looking at the relationship between lighting and how that may be affecting your weight," explained study senior author Dr. Phyllis Zee, director of the sleep disorders center at Northwestern University Feinberg School of Medicine in Chicago.

"This is an early study, but we did indeed see a fairly robust association between the amount of light and the timing of light, and weight," noted Zee. However, she was quick to point out that the study only found an association between early light exposure and lower weight, not a cause-and-effect link.

The study included 54 adults. Twenty-six were male, and the average age was 31. A special monitoring device -- worn on the wrist -- measured light exposure, sleep mid-point and duration of sleep for seven days.

Weight and height were self-reported. The researchers calculated body mass index (BMI) from those self-reported measurements. BMI is a rough estimate of a person's body fat. The participants also kept food logs during the seven days they wore the monitoring device.

Zee said the strongest association was seen in people exposed to light that was at least 500 lux, which is the equivalent of a well-lit indoor room. Outside on a sunny day provides 1,000 lux or higher, while most indoor rooms are about 200 to 250 lux, according to Zee.

But, the timing of the light also mattered. Those who were exposed to brighter light earlier in the day were the slimmest.

"For every hour later in the day that you reach 500 lux that translates to an increase of 1.28 BMI. The earlier the light exposure, the lower the BMI," said Zee.

There are a number of ways light might influence weight. One is by altering circadian rhythms -- the body's internal time clock -- to allow for better sleep. Morning light might also affect hormones that influence appetite regulation and metabolism, Zee said.

Even after the researchers controlled for other potentially slimming factors such as caloric intake, sleep duration/timing and the possibility that people getting early light exposure might be more active, light exposure still seemed to account for 20 percent of BMI, according to the researchers.

Does that mean people who live in sunnier climates would be thinner than their colder counterparts? Maybe, said Zee, though they didn't include such a comparison in the current study. "People tend to lose more weight in the summer, when you're getting more light earlier in the day," she added.

Healthy Living Tools

Ditch Those Inches

Set goals, tally calorie intake, track workouts and more, all via WebMD’s free Food & Fitness Planner.

Get Started

Today on WebMD

Wet feet on shower floor tile
Slideshow
Flat Abs
Slideshow
 
Build a Better Butt Slideshow
Slideshow
woman using ice pack
Quiz
 

man exercising
Article
7 most effective exercises
Interactive
 
Man looking at watch before workout
Slideshow
Overweight man sitting on park bench
Video
 
6-Week Challenges
Want to know more?
Chill Out and Charge Up Challenge – How to help your tribe de-stress and energize.
Spark Change Challenge - Ready for a healthy change? Get some major motivation.
I have read and agreed to WebMD's Privacy Policy.
Enter cell phone number
- -
Entering your cell phone number and pressing submit indicates you agree to receive text messages from WebMD related to this challenge. WebMD is utilizing a 3rd party vendor, CellTrust, to provide the messages. You can opt out at any time.
Standard text rates apply

pilates instructor
Slideshow
jogger running among flowering plants
Video
 
woman walking
Article
Taylor Lautner
Article