“Our study shows that the environmental light-dark cycle is important for health,” says Johanna Meijer of Leiden University Medical Center in the Netherlands. “We showed that the absence of environmental rhythms leads to severe disruption of a wide variety of health parameters.”
Those parameters included
- pro-inflammatory activation of the immune system,
- muscle loss, and
- early signs of osteoporosis.
The researchers say that the observed physiological changes were all indicative of “frailty” as is typically seen in people or animals as they age.
“The good news is that we subsequently showed that these negative effects on health are reversible when the environmental light-dark cycle is restored,” Meijer says.
To investigate the relationship between a loss of the light-dark cycle and disease, Meijer and colleagues, including Eliane Lucassen, exposed mice to light around the clock for 24 weeks and measured several major health parameters
Studies of the animals’ brain activity showed that the constant light exposure reduced the normal rhythmic patterns in the brain’s central circadian pacemaker of the suprachiasmatic nuclei (SCN) by 70 percent.
“We used to think of light and darkness as harmless or neutral stimuli with respect to health,” Meijer says. “We now realize this is not the case based on accumulating studies from laboratories all over the world, all pointing in the same direction.
Possibly this is not surprising as life evolved under the constant pressure of the light-dark cycle.
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.“
The bottom line, according to the researchers is
“light exposure matters”