Timing Light Exposure for Weight Loss

This Blog Originally Appeared on The Apeiron Center for Human Potential Website.

Life evolved on this planet under the rays of the sun. Since the advent of electricity, we have drastically altered our light environment and we are now just beginning to understand the consequences of it. Overexposure to light at night disrupts the natural circadian rhythm, a fundamental control system for nearly all the biochemical processes in our body. Our bodies work optimally when we are exposed to bright light during the day, and no light at night. In fact, every single cell in our body has circadian genes (CLOCK, BMAL1, CRY, PER and others) that regulate cellular function to some degree. 

The timing of neurotransmitters, hormones, and many other biochemical signals all wax and wane throughout the day, and the synchronized timing of these cycles is critical for good health. Imagine sitting down at a restaurant to eat a salad for lunch, and instead of having all the ingredients at once, the waiter brings out a plateful of lettuce. Then 20 minutes later, you get some tomatoes, then 30 minutes later the onions show up, and then an hour later you get a little cup of dressing as a chaser. Not so ideal, right? That’s analogous to what happens in your body when your circadian clocks are not synchronized with each other. Different biological electrochemical processes in your body are designed to function together, and when they are out of phase with each other, chaos can ensue.

Are there natural light health benefit? This and many other studies say yes.

A critical thing to understand is that there are multiple circadian clocks running in parallel in your body. You have a central circadian clock in a part of your brain called the super chiasmatic nucleus that takes most of its cues from photoreceptors in the eyes, and you have peripheral clocks in all the cells of your body. Not only is it important for the central clock to be in tune with a daily cycle, it is becoming more apparent in the research that the peripheral and central clock systems need to be in tune with each other. The overall health of your circadian rhythm depends on how in sync those two systems are with the daily cycle and with each other. What mediates this synchronization? Light!

Disrupted circadian rhythm has been shown to be associated with higher inflammation and osteoperosis, schizofrenia and bi-polar disorder, altered glucose metabolism, hypertension, and altered melatonin levels among other things. The daily cycle of melatonin and cortisol is great example of how hormones shift throughout the day and is regulated by light and dark exposure. Under ideal light exposure circumstances, Melatonin production peaks around 10-11 at night, and cortisol peaks around the time the sun rises to mobilize you out of sleep. For a more detailed look at this, see Sarah’s article on blue light and melatonin. Think of this example as a way to understand how nearly all the processes in your body change their intensity over time. 

Sleep research shows effects of morning light.But here’s the good news: You can use this knowledge to your advantage. Its not just about mitigating risk, but creating vibrant health. A study from Northwestern University showed that the time of day, the intensity, and the duration of your exposure to sunlight is linked to your weight. According to the study, people who had exposure to even relatively bright light in the morning had a lower body mass index (BMI).

“The earlier this light exposure occurred during the day, the lower individuals’ body mass index,” said co-lead author Kathryn Reid, research associate professor of neurology at Northwestern University Feinberg School of Medicine. “The later the hour of moderately bright light exposure, the higher a person’s BMI.”

The effect of morning light exposure on body weight was independent of an individual’s physical activity level, caloric intake, sleep timing, age or season.

“Light is the most potent agent to synchronize your internal body clock that regulates circadian rhythms, which in turn also regulate energy balance,” said study senior author Phyllis C. Zee, M.D. “The message is that you should get more bright light between 8 a.m. and noon.” About 20 to 30 minutes of morning light is enough to affect BMI.

The wavelengths of light present from the sun depend on the angle of refraction the sun makes as it moves through the sky. The photoreceptors in our eyes and skin are very sensitive to specific wavelengths of light which helps explains how the timing of light exposure can effect your metabolism. It is why blue light at night can be so detrimental, and why the naturally occurring spectrum of light from the sun at the right time can be beneficial.

So in order to keep off the pounds and function at your peak, make sure to get some sunlight on your eyes and skin within the first few hours of waking. The more skin exposed the better, as the peripheral photoreceptors in your skin help synchronize clock genes with the central “command center” in your brain. Personally, the first thing I do when I wake up is stand outside for a few minutes and then I eat breakfast outside on my porch where I can see the sun. I avoid wearing contacts or glasses until I leave the house to make sure I get the full spectrum of light from the sun. This is because the photosensitive pigments in our eyes such as Melanopsin and Rhodopsin are sensitive to UV A and B light. Most glass and contact materials block UV-B light.

Just as the ancestral or paleo community seeks to return to the the original ways we ate as a species, following this ideal in the way we interact with our light environment is a key to health. We cannot isolate food or exercise from the other parts of our lives and expect to see optimum functioning if we don’t optimize the other areas as well. While it may seem counter-intuitive at first that light effects us so deeply, put it in an evolutionary context and it all makes sense. Humans evolved with skin exposed to the sun and no artificial lights at night. As science makes more and more progress with understanding our relationship to light, more evidence is showing that these first principles are what will guide us to better health. So, go get some sun and synchronize your rhythm!

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