Early risers have lower body mass index

There might be more advantages to being an early bird other than getting the worm — scientists have discovered that people exposed to bright light before noon had significantly lower body mass indexes (BMI) than people who get most of their light exposure later in the day.

The study, performed by scientists from Northwestern University, has been the first one ever to link an individual’s BMI, a measure of body fat based on height and weight (not to be confused with a measure of pure body fat), to the timing, intensity and duration of light exposure. The scientists studied 54 people of an average age of 30 in the Chicago area. Each participant wore a wrist monitor that measured their light exposure and sleep parameters for seven days under normal-living conditions. They recorded what they ate on food logs so the researchers could determine caloric intake over the seven day period.

The researchers found that those who were regularly exposed to more morning light between 8 a.m. and 12 p.m. had lower BMIs. The effect counts for roughly 20 per cent of BMI, even after accounting for variables such as age, physical activity level, sleep timing, season and caloric intake. They even discovered the minimum brightness threshold for having a lower BMI: 500 lux.

The scientists were not at all surprised by this — previous research from Northwestern as well as other universities show that light plays a role in regulating metabolism, hunger and satiety. The new discovery helps support the growing evidence that keeping our internal body clocks synchronized with the natural light-dark cycle is beneficial for our health. However, the exact mechanism of how exactly light affects BMI and body fat has not been discovered yet, so the relationship between morning light and a healthy body weight cannot be labeled as a direct cause and effect.

Even though the correlation between the brightness, duration, and timing of morning light exposure and BMI is still being debated, the Northwestern researchers hope that people will be able to benefit from the research. They see it as a potential factor in weight management programs where light manipulation could be another way to help people lose weight.

This is great news for all the morning larks out there, but what about us night owls? It is pretty tough for any of us to get our daily dose of bright light in the morning – the American lifestyle is predominantly indoors and the Hopkins lifestyle is predominantly in the library, where we work in poorly lit rooms that are usually about 200 to 300 lux, which is short of the magic number the study recommends: 500 lux. The scientists agree that it is difficult to achieve a level of 500 lux indoors, but even on a cloudy day, outdoor light is more than 1,000 lux of brightness.

This means that the best way to soak in early morning bright light would be to go out for a 20 to 30 minute walk or jog. Just sun bathing on the beach works too. Freshman Michael Guo agrees that it would be beneficial to wake up early and soak in some morning rays, but not if it means sacrificing a few precious hours of sleep on the weekend. “Honestly, I rather just catch up on some sleep,” Guo said in an interview with the News-Letter.