The findings held up even when the amount of food and the physical activity of the mice were held constant, and the results could apply to people who eat meals late at night.
The researchers suggested that modern society's 24-hour-a-day schedule may be having an impact on metabolic function and weight gain.
Live Science reports:
"... [P]revious work has shown hormones that aid in metabolism are affected in humans exposed to light at night ... Night light could have reduced those hormones in mice, and coupled with a disruption in the mice's internal clocks, could have been responsible for their weight gain."
You may think nothing of turning on your bathroom light in the middle of the night or sleeping next to the glow of your clock radio. But powerful research is emerging that shows exposure to light during the night can seriously impact your body's internal clock, leading to metabolic changes and weight gain.
In fact, mice that were exposed to dim light during the night gained 50 percent more weight over an eight-week period than mice kept in complete darkness at night. They also had increased levels of glucose intolerance, a marker for pre-diabetes.
The weight gain occurred even though the mice were fed the same amount of food and had similar activity levels, and the researchers believe the findings may hold true for humans as well.
How Does Light Impact Your Weight?
When mice were exposed to night light, they ended up eating more of their food when they would normally be sleeping and this lead to significant weight gain. However, in a second experiment when researchers restricted meals to times of day when the mice would normally eat, they did not gain weight, even when exposed to light at night.
This suggests that the timing of your meals, for instance eating late at night when you'd normally be sleeping, may throw off your body's internal clock and lead to weight gain. In this case, the artificial light, such as a glow from your TV or computer, can serve as the imputes for keeping you awake and, possibly, eating, when you should really be asleep.
In other words, while it's typically thought that your biological clock is what tells you when it's time to wake up or go to sleep, light and dark signals actually control your biological clock. In turn, your biological clock regulates your metabolism.
So when your light and dark signals become disrupted it not only changes the times you may normally eat, it also throws your metabolism off kilter, likely leading to weight gain.
Why it's So Important for You to Sleep When it's Dark Out
Your biological clock, or circadian rhythm, has evolved over hundreds of generations to align your physiology with your environment, and your body clock assumes that, like your ancestors, you sleep at night and stay awake during daylight hours.
If you confuse the situation by staying up late and depriving yourself of enough hours of sleep, or even eating meals at odd hours (times at which your internal clock expects you to be sleeping), you send conflicting signals to your body.
One way this occurs is by altering levels of important hormones linked with appetite and eating behavior. When you are sleep deprived, your body decreases production of leptin, the hormone that tells your brain there is no need for more food. At the same time it increases levels of ghrelin, a hormone that triggers hunger.
In one study, researchers found people who received only four hours of sleep a night for two nights experienced:
- 18 percent reduction in leptin
- 28 percent increase in ghrelin
Also, the sleep-deprived subjects in the study seemed to eat more sweet and starchy foods, rather than vegetables and dairy products. Researchers suspected these cravings stemmed from the fact that your brain is fueled by glucose (blood sugar); therefore, when lack of sleep occurs, your brain searches for carbohydrates.
In short, sleep deprivation puts your body into a pre-diabetic state, and makes you feel hungry, even if you've already eaten.
Your sleep habits also directly influence weight gain around your abdominal area. This is the type of fat linked to heart disease, type 2 diabetes, strokes and other chronic diseases, so it's a matter that goes way beyond aesthetics.
Another Important Reason to Sleep in Total Darkness …
Your weight is not the only factor at risk if you frequently leave lights on at night.
A part of your brain called the Suprachiasmatic Nucleus (SCN) -- a group of cells in your hypothalamus -- controls your biological clock. And the cells that make up your SCN respond to light and dark signals.
Light actually travels through your eye's optic nerve to your SCN, where it signals your body's clock that it's time to wake up. Light also signals your SCN to initiate other processes associated with being awake, such as raising your body temperature and producing hormones like cortisol.
Meanwhile, when your eyes signal to your SCN that it's dark outside, your body will begin to produce melatonin. The level of melatonin produced is related to the amount of exposure you have had to bright sunshine the previous day; the less bright light exposure the lower your melatonin levels.
Melatonin is a hormone that helps you sleep and radically decreases your risk of cancer. There are many studies on this powerful association. The more your sleep is disrupted by light pollution, the lower your melatonin levels and the greater your risk of developing cancer becomes.
Melatonin is secreted primarily in your brain and at night it triggers a host of biochemical activities, including a nocturnal reduction in your body's estrogen levels. It's thought that chronically decreasing your melatonin production at night -- as occurs when you're exposed to nighttime light -- increases your risk of developing cancer.
In fact, one of the first studies linking cancer to light showed that blind women have a 36 percent lower risk of breast cancer compared to sighted women. Why? Because they are unreceptive to light. This means that their bodies maintain high melatonin levels at night regardless of how much light is in the room.
If you have to use a light at night, you should only use a red light or nightlight as that is the wavelength that will have virtually no influence on your pituitary gland to produce melatonin. When you are exposed to any other color at night your melatonin levels will drop like a rock and if this occurs regularly it will increase your risk of cancer.
Tips for Creating a Dark Sleep Sanctuary
Your body works best when it is exposed to predictable patterns of light and darkness. Unfortunately, once artificial light was developed less than a century ago, it varied the length of a day so that humans are now exposed to completely unpredictable patterns of light and dark.
The irregularity prevents circadian rhythms from adjusting to a pattern, and creates a state of permanent "jet lag."
The solution, of course, is to make your sleep-wake cycle, and your light-dark patterns, as predictable as possible by:
- Going to sleep as early as possible and waking up early
- Keeping your bedtime and wake times at the same times each night and morning
- Eliminating artificial light when it's time to sleep
Personally, I sleep in a bedroom that is so dark I can't see my hand in front of my face. Even the dim glow from your clock radio could be interfering with your circadian rhythm, and therefore also your weight and risk of cancer, so it's incredibly important to keep your bedroom dark.
To get your bedroom as dark as possible:
- Install blackout drapes
- Close your bedroom door if light comes through it, and even put a towel along the base to prevent light from seeping in
- Get rid of your electric clock radio (or at least cover it up at night)
- Avoid night lights of any kind
- Keep all light off at night (even if you get up to go to the bathroom) -- this includes the TV!
- If you can't get your bedroom dark enough, wear an eye mask to block out any stray light
These tips are incredibly simple, but they have the potential to make an enormous impact on your health and weight. I encourage you to do a "light check" in all of your family members' bedrooms to ensure they're each sleeping in the pitch-black environment that is best for optimal health.
If you are interested in finding more information on this fascinating subject, I highly suggest reading Lights Out: Sleep, Sugar, and Survival by T. S. Wiley and Bent Formby. The authors believe that it is light, not what we eat or whether we exercise, that causes obesity -- and diabetes, heart disease and cancer.