Every day, people are exposed to hours of artificial light from computers, office lights and even 24-hour lighting in hospitals.

Every day, people are exposed to hours of artificial light from computers, office lights and even 24-hour lighting in hospitals.

Now, new research in animals shows that excessive exposure to ��light pollution�� might be worse for you than previously known, taking a toll on muscles and bones.

Researchers at Leiden University Medical Center in the Netherlands tracked the health of rats exposed to six months of continuous light compared with a control group of rats living under normal conditions � 12 hours of light, followed by 12 hours of dark.

During the study, reported in Current Biology, the rats exposed to continuous light had less muscle strength and showed signs of early-stage osteoporosis. They also got fatter, and some markers of immune system health worsened.

While earlier research found excessive light exposure might affect cognition, the new research showed a surprising effect on muscles and bones.

��Not only did motor performance go down on tests, but the muscles themselves just atrophied, and mice physically became weaker after just two months,�� said Chris Colwell, a sleep specialist at the University of California-Los Angeles, who was not involved with the study.

The good news is the effects of light exposure appear to be reversible. When the study rats returned to their natural light-dark cycle, their health returned to normal after two weeks.

The data suggest more research is needed into the health effects of artificial light. One concern is the health of patients in hospital intensive care units, people in nursing homes and babies in neonatal units � places where artificial lights often are kept on for 24 hours a day.

��We keep the sickest people in our society under constant light conditions,�� Colwell said.

The research also might have implications for people exposed to the blue wavelength light emitted from computers, which might be more disruptive to the body than the light that comes from traditional artificial lights.