: Lynn Celmer, 630-737-9700, ext. 9364, 
– A new study suggests that the timing of exposure to moderate levels of light may influence body mass index (BMI) and body fat.

Results show that people with more exposure to moderate or higher intensity light earlier in the day had lower body mass index and percent body fat than those with more of their moderate or higher intensity light exposure later in the day.

“These results emphasize the importance of getting the majority of your exposure to moderate or higher intensity light during the morning and provide further support that changes to environmental light exposure in humans may impact body weight regulation,” said study co-author Ivy N. Cheung, a doctoral candidate in the Interdepartmental Neuroscience program at Northwestern University in Chicago, Illinois.

The research abstract was published recently in an online supplement of the journal Sleep and will be presented Tuesday, June 9, in Seattle, Washington, at SLEEP 2015, the 29th annual meeting of the Associated Professional Sleep Societies LLC.

The study group comprised 23 healthy adults. The majority were female, with a mean age of 26 and a mean BMI of 29.  Subjects wore a wrist monitor for seven days to determine light patterns. Seventeen participants also had the total percentage of body fat measured using dual axis absorptiometry (DXA). Light data was binned into 2 minute epochs, smoothed using a 10-minute moving average, and then aggregated over 24 hours for each individual. The mean light timing above a threshold light level C (MLiTC) was defined as the average clock time of all aggregated data points above C lux with thresholds ranging from C=20-2,000 lux at 20 lux intervals. Height and weight were objectively measured to determine BMI.

The research was performed under the supervision of Dr. Phyllis C. Zee, MD, PhD, in the Circadian Rhythms and Sleep Research Laboratory at Northwestern University. The study was supported with funding by the National Institutes of Health (NIH).

Abstract Title: Mean Light Timing is Correlated with Body Mass Index and Body Fat in Adults
Abstract ID: 0211
Presentation Date: Tuesday, June 9
Presentation Type: Poster 53
Presentation Time: 4 p.m. to 6 p.m.

The SLEEP 2015 abstract supplement is available at

For a copy of the abstract or to arrange an interview with the study author or an AASM spokesperson, please contact AASM Communications Coordinator Lynn Celmer at 630-737-9700, ext. 9364, or

About SLEEP 2015

More than 5,000 sleep medicine physicians and sleep scientists will gather at SLEEP 2015, the 29th annual meeting of the Associated Professional Sleep Societies LLC (APSS), which will be held June 6-10 at the Washington State Convention Center in Seattle. The scientific program will include about 1,200 research abstract presentations. The APSS is a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society ( 

About the American Academy of Sleep Medicine
Established in 1975, the American Academy of Sleep Medicine (AASM) improves sleep health and promotes high quality patient centered care through advocacy, education, strategic research, and practice standards. With nearly 10,000 members, the AASM is the largest professional membership society for physicians, scientists and other health care providers dedicated to sleep medicine (