Researchers have found that mice exposed to artificial light around the clock suffer a range of health consequences, according to a study published Thursday in the journal Current Biology.
Advertisement
The light-bombarded mice showed inflammation, muscle weakness and bone loss. In other words, the classic signs of frailty, which is typically a normal part of aging in people and animals—except that the mice in the study were not old.
Most of us do not live under uninterrupted light for six months like these mice did, but the findings highlight the consequences of meddling with the natural day-night cycle.
“We used to think of light and darkness as harmless or neutral stimuli with respect to health,” study co-author Johanna Meijer, of the Leiden University Medical Center in the Netherlands, said in a statement. But growing evidence from laboratories all over the world suggests the opposite, she added.
“Possibly this is not surprising as life evolved under the constant pressure of the light-dark cycle,” Meijer said. “We seem to be optimized to live under these cycles, and the other side of the coin is that we are now affected by a lack of such cycles.”
Advertisement
A Light-Powered Clock In The Brain
The premature aging in the mice can likely be traced to the nighttime light’s harmful effect on their brains’ circadian clock, according to the researchers.
After living for six months in brightly lit cages, the animals showed a 70 percent reduction of the normal rhythmic patterns in their brains’ central clock, a tiny group of 20,000 neurons in the hypothalamus called the suprachiasmatic nucleus (SCN).
Guided by the information from light-sensitive cells in the eyes, the SCN controls daily hormonal activities in the body over a 24-hour cycle. In the case of the mice, the SCN constantly received signals from those light-sensitive cells for six months. (Even with the eyes closed during sleep, a portion of the light still reaches the cells on the retina.)
Though mice are not people, a host of other studies suggest that light has similar effects on our own circadian clock: Too much exposure to artificial light breaks our natural sleep patterns. This in turn leads to health problems ranging from mood disorders to diabetes. Shift workers, for example, have an increased risk for heart disease. Sleep-deprived people may gain weight because their brains respond differently to high-calorie food. People with disrupted rest due to sleep apnea show poor bone health.
Turn The Darkness Back On
As for the darkness-deprived mice, they exhibited less strength and lower skeletal muscle function in standard tests. Their bone density decreased, and they showed signs of an activated immune system.
Advertisement
The good news, researchers said, was that those effects were reversible.
Two week after the mice were returned to a normal light-dark cycle, their SCN neurons got back in normal rhythm, and their health problems improved.
People don’t need to be part of a study to experience a disturbed day-night cycle. Up to 80 percent of the world’s population lives under artificial light during the night. Light pollution may grow even more as energy-efficient but high-intensity LED streetlights replace traditional street lamps, a Science research article noted last month.
Recently the American Medical Association also warned against the health effects of LED streetlights. Rich in blue light, LEDs may have up to five times greater impact on circadian rhythms than conventional street lamps, according to the AMA.
The medical group pointed out that brighter residential nighttime lighting is linked with reduced sleep, low sleep quality, sleepiness, impaired daytime functioning and obesity.
Advertisement
So shut the light out, and if you can’t, invest in an eye mask.
Our 2024 Coverage Needs You
It's Another Trump-Biden Showdown — And We Need Your Help
The Future Of Democracy Is At Stake
Our 2024 Coverage Needs You
Your Loyalty Means The World To Us
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
The 2024 election is heating up, and women's rights, health care, voting rights, and the very future of democracy are all at stake. Donald Trump will face Joe Biden in the most consequential vote of our time. And HuffPost will be there, covering every twist and turn. America's future hangs in the balance. Would you consider contributing to support our journalism and keep it free for all during this critical season?
HuffPost believes news should be accessible to everyone, regardless of their ability to pay for it. We rely on readers like you to help fund our work. Any contribution you can make — even as little as $2 — goes directly toward supporting the impactful journalism that we will continue to produce this year. Thank you for being part of our story.
It's official: Donald Trump will face Joe Biden this fall in the presidential election. As we face the most consequential presidential election of our time, HuffPost is committed to bringing you up-to-date, accurate news about the 2024 race. While other outlets have retreated behind paywalls, you can trust our news will stay free.
But we can't do it without your help. Reader funding is one of the key ways we support our newsroom. Would you consider making a donation to help fund our news during this critical time? Your contributions are vital to supporting a free press.
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. Would you consider becoming a regular HuffPost contributor?
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. If circumstances have changed since you last contributed, we hope you'll consider contributing to HuffPost once more.