People exposed to morning light have lower body mass
A new Northwestern Medicine study suggests that timing, intensity, and duration of sunlight exposure during the day is directly linked to your weight.
The study included 54 participants (26 males, 28 females) at an average age of 30. To track their behavior, they wore a wrist actigraphy monitor that measured their light exposure and sleep parameters for seven days in normal-living conditions and their caloric intake was determined from seven days of food logs.
The study found that people who had most of their daily exposure to even moderately bright light in the morning had a significantly lower body mass index (BMI) than those who had most of their light exposure later in the day. Also, the influence of morning light exposure on body weight was independent of an individual's physical activity level, caloric intake, sleep timing, age or season. It accounted for about 20 percent of a person's BMI.
The research team says that the finding emphasizes the importance of “circadian health” in which exposure to light and dark is synchronized with your internal body clock.