Light — Not Always Enlightening

The best scientists make connections between work and life. Rebecca Boyle wrote,

Randy Nelson, a circadian biologist at Ohio State University, has been studying light’s effects on depression and obesity since 2004, when one of his graduate students was hospitalized for a staph infection. The student complained bitterly about the bright lights in his room and in the hospital hallway, which robbed him of sleep and stressed him out.

Back at the lab, Nelson and grad student Laura Fonken brought in special rodents, and kept the lighting in their quarters relentlessly bright, like a maximum-security prison. The subjects became listless and depressed, with glitches in their learning abilities and memory, and they even lost their taste for sugar-water treats.

Then the researchers tried providing only a little bit of night illumination in the rat barracks — what in human terms would be the equivalent of leaving a computer or TV screen on in the bedroom. They got the same result — mopey rodents who were definitely not at the top of their game. Apparently, low-quality sleep affects organisms like low-quality food. It can keep a creature alive and functioning, but it is not capital-L Life.

And now the bad news

Also, the experimental animals got fat, and here is the scary part: “They were eating the same number of calories as their dark-sequestered mates.” What was going on? The answer Nelson and Fonken came up with was that light-activated messenger RNA molecules go around switching genes off and on, and this regulates circadian rhythms.

Messing with the process comes with a price tag. Without knowing every last detail, they concluded that the link could not be doubted. Just like malnourishment, sleep interference can, and will, find a way to forge an inevitable path toward obesity.


Epidemiologist Richard Stevens of the University of Connecticut explained to journalist Boyle the actions of the hormone melatonin, which lowers the body’s core temperature and induces drowsiness. In animals with backbones, from fish to humans, melatonin regulates the sleep-wake cycle and calibrates the metabolism. Stevens explained,

Production of melatonin should begin at dusk, when we are supposed to sleep. Light — not wakefulness itself, but light — shuts it off.

Over the next few years, some research here and there continued to link nocturnal artificial light with an increased risk of weight gain. It was hard to prove the particulars of causation. In 2019 a study showed that, for women middle-aged and above, illumination in the hours of darkness was paired with a higher likelihood of obesity. As it turns out, the light does not even need to be as bright or concentrated as a device’s screen. Apparently, damage can be done by seepage through and around curtains, and by clocks that glow in the dark.

A study led by Dr. Yong-Moon Park involved “almost 44,000 generally healthy women, ages 35 to 74.” What happened?

Many — about 17,000 — slept with a nightlight in the room, while more than 13,000 left a light on outside the bedroom and about 5,000 slept with a television or light on in the bedroom.

After almost six years of follow-up, women who slept with a television or light on in the room were 22 percent more likely to be overweight and 33 percent more likely to be obese than women who slept in total darkness without even a nightlight or the glow from an alarm clock.

Whether or not the subjects had “enough” hours of sleep, what made the difference was the artificial light during sleep time.

Your responses and feedback are welcome!

Source: “The End of Night,”, 04/01/14
Source: “Sleeping with lights or TV on tied to obesity,”, 06/10/19
Image by Evan/CC BY-ND 2.0

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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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