Timing of exposure to light influences Body Mass Index

The timing of exposure to moderate levels of light may influence body mass index (BMI) and also body fat, says a new study.

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 PhD student at Northwestern University in Chicago, Illinois.

The study was presented at the 29th annual meeting of the Associated Professional Sleep Societies LLC in Seattle, Washington. For the study, 23 healthy adults, the majority being female, with a mean age of 26 and a mean BMI of 29, were recruited. They wore a wrist monitor for seven days to determine light patterns.

Seventeen participants also had total percentage body fat measured using dual axis absorptiometry (DXA). Light data was sent into 2 minute epochs, smoothed using a 10-minute moving average, and then aggregated over 24 hours for each individual.

Height and weight were objectively measured to determine BMI.