LEIDEN, Netherlands, July 15 (UPI) -- The right balance of light and dark is essential to health, new research suggests. Scientists have found mice that are subjected to a constant barrage of bright light suffer myriad health issues.
"We came to know that smoking was bad, or that sugar is bad, but light was never an issue," researcher Johanna Meijer, a neuroscientist at Leiden Medical Center, told Nature News. "Light and darkness matter."
A number of studies have found links between artificial light, sleep problems and a variety of health issues, including cancer, diabetes and cardiovascular disease. Several studies have identified a heightened risk of disease among night-shift workers.
But proving a direct connection between light and poor health has proven difficult.
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In the search for such a link, a team of researchers led by Eliane Lucassen flooded the cages of a group of mice with bright light. The experiment lasted 24 weeks. Though the mice could close their eyes when they slept, they were still exposed to significantly more light than during a normal day-night schedule.
Electrode implants tracked the neuronal activity of the mice. The electrodes revealed irregular patterns among the neurons that control the animals' pacemakers. The mice also augmented their sleep cycle, adopting a 25.5-hour day.
The constant light diminished their bone density, weakened their muscles and hampered their forearm strength.
Once exposed to a normal light-dark schedule, the neurons normalized and the mice returned to a 24-hour day. They also regained their strength, as well as proper bone density.
Researchers published their findings in the journal Cell Biology.
"These findings strongly suggest that a disrupted circadian rhythm reversibly induces detrimental effects on multiple biological processes," researchers wrote.
The scientists say more research is necessary to determine whether bright light has similar effects on humans. Meijer and Lucassen are planning to study the effects of bright light on grass rats, which are active during the day and sleep at night, unlike lab rats.
Even without additional research, the scientists say more and more findings all point to the basic fact that light exposure matters.
"Possibly this is not surprising as life evolved under the constant pressure of the light-dark cycle," Meijer said in a news release. "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."
