Fattening Darkness: The dark side of artificial light.

When it comes to weight management, the timing of dining is pivotal, at least in rodents, food proved especially fattening when consumed at the wrong time of day, according to a study made by the Ohio State University in Columbus.As nocturnal animals, mice normally play and forage at night, often in complete darkness. With even dim chronic illumination of their night time environment, the animals’ hormonal dinner bells rang at the wrong time.Therefore, the mice began eating most of their chow during what should have been their rest period. The result: They fattened up and developed diminished blood-sugar control. 

It is not the light itself that made the mice fat. Rather the light at night disrupts a biological process called the circadian clock; this clock is in the brain of every mammal and tells the body, for example, when to sleep, when to eat and when to burn calories. The clock responds to the amount of light around, so if the light changes the clock may change, meaning that a body may get confused about what to eat and when to eat and how to burn calories.

In the study, the mice were divided into three groups. One group was exposed to the standard amount of light and dark: 16 hours of light and eight hours of darkness. The second group lived in light for 16 hours but spent the other eight hours in dimmed light. The last group lived in bright light 24 hours every day.

After one week into the experiment, the researchers noticed that the second and the third group (the ones exposed to dimmed and 24 hour light) started to gain weight. After 8 weeks the third group of mice weighted considerably more than the mice in the standard group. Since all 3 groups had the same amount of food and the same environmental situations, the big surprise is that the fatter mice did not gain weight because they ate more but because they ate at different times.Throughout the eight-week study, their caloric intake—and output through exercise—matched that of lean kin afforded a truly dark night.

Mice are naturally nocturnal. That means they are active at night, which is when they eat the bulk of their food. In the standard group, the mice ate only one-third of their daily food intake in the light. But mice in the dim-light group ate more than half of their food during the same time. That suggests that light at night resets the body’s biological clock and sends an „eat now“ signal to the brain at the wrong time. A dimly lit night somehow encouraged animals to down most of their food at a time when their biological clocks weren’t expecting it and when their bodies were unprepared to efficiently burn the incoming calories. Such data is very consistent with a growing realization that our lighted environment can damage our health in a number of different ways.

In a second set of experiments, some animals were allowed to eat at will; others could eat only during the light phase or only during the night phase. Animals exposed to dim light at night again grew faster and fatter, except when they were forced to eat during the night. Then they remained slim like those that had encountered eight hours of total darkness nightly.Although 5 lux is sufficient to alter a rodent’s circadian rhythms, the daily cycles orchestrated by an animal’s internal clock (it’s probably not relevant to humans), however, many people encounter much brighter light than that for hours every evening. If they continue to eat during these naturally dark periods, that food might encounter a sleepy metabolic system. Just as a low-temperature flame may fail to fully burn a log, a slow metabolic system may leave some calories unburned and then store the residual as fat.

While light at night appeared to reset the biological clock’s time-to-eat signals, other studies have shown that changing meal times can also reset the clock. As such, chronically dining at other than the times of day the species evolved to eat may amplify light’s disruption of the biological clock. What’s going wrong may involve the sympathetic nervous system, meaning the brain control that can prepare the body for fight when it’s stressed. Other related studies have shown that tinkering with this system diminishes healthy blood sugar control.

The similarly elevated blood sugar seen in the study’s dim-night mice suggests they are under stress and their sympathetic nervous system is being affected. Humans are not a nocturnal species, when eating at night (as nocturnal animals) we send emergency messages to the hypothalamus which answers with a discharge of stress hormones that make our body to store fat. Just because we’re not mice doesn’t mean we’re off the hook. The researchers noted in their study that around the world, there’s a connection in human beings between obesity and increased exposure to light at night. Some people have to work the night shift; others stay up in front of their computers or televisions.

Just by turning on the light of the bathroom in the middle of the night, sleeping with the television on or checking up the mobile phone in the middle of the night may increase the risk of gaining weight because of the light. Some light sources produce a high blue color in their spectrum; Melanopsin containing retinal ganglion cells are sensitive to blue light and project to the hypothalamus where they can control rhythms and eating behavior. But not only the light is the antagonist of the story, noise of the street, a snoring sleeping neighbor or sleeping problems are also sources for disrupting the normal development of our circadian cycle. The sleeping period is more important for loosing weight than the way of eating. Not getting enough sleep affects serotonin increasing the appetite and the preference for sweets, it also causes insulin resistance and abnormal increase in blood sugar after eating carbohydrates.

Altering our circadian rhythm means altering our daily rhythms. Some facts related to our rhythms and our behavior are: eating carbohydrates in the dawning fattens twelve times more than eating the same carbohydrates in breakfast; as example, having a hot dog with french fries after going out on the weekend and before going to sleep makes you gain more weight than if you have the same food during lunch time. Cholesterol is produced during nighttime, changing our light situations may compel our body to produce it in different times and then health problems may come with the time. Testosterone levels in our body rise early in the morning, that is the reason of why acne pimples mostly appear in the mornings.

Blood pressure, melatonin, serotonin, strength, among others are also involved with our circadian rhythm and the disrespect those rhythms bring consequences. Not sleeping enough or disrupting the sleeping process is unhealthy, those who work at night or don’t get easily sleep suffer of overweight cause by hyperinsulinism. Lack of sleep proved to increase appetite and anxiety for candies, fibromyalgia meaning extreme fatigue, body pain and headaches. Other consequences from the absence of sleep are abnormal levels of the uric acid, riglycerides and cholesterol, as well infertility and hair loss. Blue light has proved to stop the production of melatonin; melatonin is a powerful, protective neuroendocrine substance that as shown the ability to inhibit tumor growth and strengthen anticancer immune defenses. Darkness during the night is crucial to loose weight or at least to not gain weight. Having the right sleeping habits is not hard, for example, if you are going to get up in the middle of the night, it is better to use lights that are not overly bright. That’s because turning a bright light on even briefly may stopp melatonin secretion, which may not start up again for up to 20 minutes after the light is turned off. It may not reset your body clock, but it could get in the way of you getting back to sleep quickly. The eyes are photosensitive even when we sleep, ganglion cells in our retinas can absorb light photons through our eyelids (though they absorb less than when eyes are open). In short, if there’s a light burning somewhere, our bodies know it, even deep in sleep. To reduce light exposure when sleeping, remove electronics from the bedroom. If your alarm clock is bright, turn it around so it’s not facing you. If there are streetlights outside your window, shut the curtains and if there is still too much light, you might consider investing in blackout screens.

Yet, even when we set out to correct the imbalances in our artificially lit world, we can run into challenges. Light pollution, or light from poorly designed lighting systems that send light skyward (where it is unneeded and unwanted), occludes natural darkness in densely inhabited areas and thwarts our efforts to experience daily doses of darkness. As much as we want to live in a 24-hour day, we evolved with daily light and dark periods, and our circadian cycles are a constant reminder of this fact(1). Light pollution also robs us of experiencing moonlight and starlight. While there’s very little research on the human health effects of exposure to it, and the research so far shows no quantifiable connection between exposure to celestial light and our natural rhythms, the psycho-emotional benefit of experiencing that light is hard to deny.

Our brighter world comes with many advantages including gains in convenience, productivity, comfort and safety. We can influence these benefits for the best, however, that brighter world is only entirely improved when we understand how our bodies work in connection with natural cycles of light and dark, and when we know when to turn lights off as well as on.


(1) The International Dark-Sky Association (IDA), “Physiologically, humans need darkness”


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