Could simply exposing yourself to the right kind of light help you lose weight?

Researchers at Northwestern University think so. And they have the studies to back up their assertions. What’s more, we’re not talking about losing just a couple of pounds. The effect of light appears to be quite large.

These scientists believe our indoor artifical light environment is an important reason so many people are overweight. Added to that, we get our bright light at the wrong time, throwing off the body’s natural circadian rhythm, playing havoc with our blood sugar and warping the way our bodies use the calories in our food.

But you can do something about it and possibly make it easier to keep off extra pounds. . .

Circadian Rhythm

The Northwestern investigation shows that the length of your exposure to bright light, how intense the light is and the time of day you’re in the light is linked to how much you weigh.1

The research analyzed the relationship between light exposure and the weights of 54 men and women. The folks who experienced most of their daily exposure to bright light in the morning (even if it was only moderately bright light) had a significantly lower body mass index when compared to people who had most of their light exposure at a later time in the day. Body mass index – BMI – is calculated from an individual’s height and weight. It’s a frequently used gauge of healthy vs. unhealthy weight.

The relationship between body weight and exposure to morning light persisted in the researchers’ analysis even when taking into account how many calories a person ate, how long and at what times they slept every night, how old they were and the time of the year. The light exposure, say the scientists, accounted for a full 20 percent of every person’s BMI.

If that holds up, it’s a remarkable finding.

Good Lux and Bad

The physiological mechanism that makes light so important for body weight, according to the Northwestern U. researchers, is that it affects the body’s circadian (daily) rhythm, which influences the body’s metabolism — how fast it burns calories and how it distributes energy to the cells in the body.

“Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance,” said researcher Phyllis C. Zee. “The message is that you should get more bright light between 8 a.m. and noon.”

She adds that you only need about 20 to 30 minutes of strong morning light to help lower your BMI.

Zee also says that many Americans don’t get sufficient natural light in the early part of the day because we spend so much time indoors. Our offices and homes are poorly lit, often with only about 200 to 300 lux of light (lux is a measurement of illumination).

In contrast, being outdoors offers more than 1,000 lux of brightness even when it’s cloudy. And you need at least 500 lux in the morning to help keep your circadian rhythm on track.

Dim The Lights at Night

Another study by these researchers demonstrates that bright light at night should be avoided to help keep your blood sugar down and avoid insulin resistance – which is often a precursor to diabetes.2

“Our findings show that insulin was unable to acutely bring glucose levels back to a baseline level following a meal with bright light exposure in the evening,” says researcher Ivy Cheung. “The results of this study emphasize that our lighting environment impacts our health outcomes.”

So for lower weight and better blood sugar, turn off the video screens at night and get out in the sun in the morning. Your waistline will probably thank you.


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3973603/
  2. http://www.ncbi.nlm.nih.gov/pubmed/27191727