Angelenos are blessed with an ample number of sunny days, thanks to Southern California’s Sunbelt location. A new study has reported another advantage to sun exposure; it found that exposure to early morning light can be extremely effective in keeping off excess poundage. The study was published April 2 in the journal PLOS ONE by researchers at Northwestern University, Feinberg School of Medicine in Chicago, Illinois.
The study authors note that studies have reported that morning light exposure affects body fat and the level of appetite regulating hormones; however, none have assessed the influence of both light levels and sleep on body weight in humans. Therefore, the conducted a study to determine whether the timing and intensity of light exposure (particularly in the morning) would relate to a lower body mass index (BMI) independent of sleep duration and timing.
The study group comprised 54 individuals (26 males; average age: 30.6 years) who were recruited from the community through advertisements for a study of circadian rhythms and sleep patterns. Light levels as well as sleep midpoint and duration were measured with a device by actigraphy (Actiwatch-L). The device digitally records gross motor activity (movement) that can be used to visualize rest activity patterns as well as light-intensity. The subjects wore the device for one week. BMI was obtained from self-reported height and weight. Caloric intake during the entire week was obtained from food logs.
The researchers found that individuals having the majority of the average daily light exposure above 500 lux earlier in the day was associated with a lower BMI; furthermore, every hour that exposure was delayed corresponded with a 1.28 unit increase in BMI.
Study leader Kathryn Reid, PhD explained that light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance. She noted that many individuals fail to obtain adequate light in the morning. She recommends that, in view of the study results, workplaces and schools should have more windows, and employees and students should be encouraged to spend morning breaks outside, Bright daylight provides exposure of 10,000 lux, and even on an overcast day light levels of 1,000 lux are present.