An interesting new study published by researchers at Northwestern University reported in PlOS One found that people who get up and out of the house in the a.m., are less likely to be overweight or obese, compared to those who get most of their exposure to outdoor light later in the day.
This study adds to the growing body of scientific evidence that suggests that hours of sleep and the body’s natural circadian rhythm play an important role in your metabolism, hunger and appetite regulation. This helps us better explain why shift workers and night owls are more likely to be overweight. It may also be why so many people gain weight in the winter months, when they get little exposure to natural light in the a.m.
In the study, 54 adults wore wrist monitors that tracked sleep time and duration and activity as well as the exposure to light and the intensity of the light. Their results found a correlation between exposure of light >500 lux and lower BMI values. Indoor lighting is between 150-500 lux while offices are usually around 200-300 lux. In comparison, the light at high noon could be around 120,000 lux and an overcast day will provide 1,000-2,000 lux.
Whether it’s light or dark out is what controls our internal body clock to regular circadian rhythms. If you aren’t getting exposure to light early in the day, it may set up hormonal changes in your body that drives up your appetite and may suppress your metabolism. The best time to get adequate exposure to sunlight (even if it’s cloudy out) is between 8 a.m. and noon. The researchers also found that just 20-30 minutes of morning light is adequate to help control your weight.
What you can do:
To put the results of this study into practice, consider shifting your sleep habits so that you get are awake and get outside in the early a.m., and strive to get at least 7 hours of sleep per night. If you can go for a walk, jog or even a swim practice in an outdoor pool, you’ll be able to help potentially shift your hormones to turn up fat burning and turn down the hormones that stimulate your hunger and appetite. And, to continue to turn down your hunger hormones, have a breakfast with 20-25 grams of protein each day.
Reid KJ, Santostasi G, Baron KG, Wilson J, Kang J, et al. (2014) Timing and Intensity of Light Correlate with Body Weight in Adults. PLoS ONE 9(4): e92251. doi:10.1371/journal.pone.0092251