More and more research is coming to light about the link between our sleeping habits and our weight. Chronic sleep deprivation has been linked to weight gain, and now it appears that the time you wake up also has a part to play.
A paper published in the Public Library of Science’s peer-reviewed resource PLOS One says that it is not only the amount of hours you sleep a night that matters, but the time you wake up too.
Those who were exposed to bright light before midday were found to have lower body mass indexes (BMI) than those exposed to more light after midday. The findings were independent of the number of calories consumed. One of the senior authors of the paper, Dr Phyllis C Zee said that as little as 20-30 minutes of sunlight before midday could affect BMI.
The key here is thought to be in the brightness of light, and the minimum brightness was revealed to be 500 lux (lux being the measurement of intensity of light at a specific distance from the light source). Light from outside typically rates at 1,000 lux on a cloudy day and 10,000 on a sunny day, while indoor light normally rates somewhere between 200 and 500 lux.
The study itself was small and used 54 volunteers who were aged just over 30. The participants documented their dietary intake and then wore wrist monitors to track light exposure and sleep patterns. While the study is considered relatively small, the findings still prove valuable.
The authors of the study suggest that when we confuse our bodies about it being day or night (for example by using blue-emitting electronic gadgets at night or by not getting enough light during the day), we delay the release of the hormone melatonin, which makes it difficult for us to sleep.
Less sleep is then thought to increase appetite as it raises the ‘hunger hormone’ ghrelin and reduces the amount of physical activity we do (as we are too tired). Being exposed to natural light in the morning helps to reduce melatonin levels and helps to regulate our circadian rhythms.