Exposure to natural light in the morning may act as a metabolic signal that promotes lower build and weight control, according to a new study in young adults.
Circadian rhythms, in particular sleep time, have been associated with weight in several studies. Shorter sleep time has been associated with alterations in hormones that influence satiety (ghrelin and leptin), increased cravings for energy-dense foods, and higher weight. But light alone, depending on the period of exposure, could influence our metabolism, independently of eating behavior.
Measurement of light and caloric intake
In any case, this is what certain studies in animals suggest, and which now finds confirmation in humans. Kathryn Reid (Northwestern University in Chicago) and her colleagues conducted an experiment consisting in measuring, in 54 adults wearing a bracelet measuring exposure to light and sleep cycles. Caloric intakes were assessed using a 7-day intake record.
A positive factor in the prevention of overweight
The results report that light exposure time early in the day is associated with lower BMI, independent of sleep time and caloric intake.
For the authors, light is a powerful biological signal, and exposure at the appropriate time (in the morning) could represent a modifiable risk factor in the prevention and management of obesity and overweight in modern societies.
Reid KJ et al. Timing and Intensity of Light Correlate with Body Weight in Adults. PLoS ONE, 9(4): e92251.