If you’re watching your weight, you might consider getting up early and going outside. A new study from Northwestern University’s Feinberg School of Medicine showed that people whose exposure to bright natural light was mainly early in the day – between 8 a.m. and noon – had a lower body mass index than people whose light exposure occurs mostly in the late afternoon. All told, the difference in weight between early birds and not-so-early types could be as much as 30 pounds, stemming entirely from the influence and timing of their light exposure, the study found. The Northwestern researchers recruited 54 people, average age 30 who wore wrist monitors that tracked their light exposure and sleep time for a week. The study participants kept logs of what they ate and how often and how much they exercised. The researchers said that the light exposure could come from various sources, including through car windows. Bright light later in the day or at night has the opposite effect – it has been linked to obesity.
Phyllis Zee et al, “Timing and Intensity of Light Correlate with Body Weight in Adults, PLOS One, DOI: 10.1371/journal.pone.0092251