Constant exposure to artificial lights can lead to a range of health consequences. Researchers conducted an experiment using mice found that exposure to excessive light has a serious impact on health, after animals are removed from the natural cycle of a day/night routine.
The experiment involved 134 mice, which experienced no darkness for 24 weeks. They were kept in brightly lit cages. By the end, the mice had lost about half their skeletal muscle function compared with controls. This was measured by grip endurance tests and their ability to cling to bars, while the signals of their internal body clocks were weakened. Their bones were affected too. The bulbous, spongy parts of their bones that are responsible for bearing most weight lost a third of their volume, and became 10% thinner, just as in the early stages of osteoporosis. There were also signs of increased inflammation, such as a rise in the number of neutrophil white blood cells - usually associated with stress or infection. The animals showed a 70% 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.
‘Excessive and untimely exposure to artificial light disturbs the body’s natural circadian rhythm and creates a host of health problems. The environmental light-dark cycle is important for health.’
In humans too, excessive exposure to artificial light disturbs the natural sleep patterns. Not to mention people in nursing homes and hospitals who often sleep with some lighting on, which they can't control and shift workers, who may find it hard to block out the day's light when they rest. Other people just sleep with the glow of their computer going at all times. This in turn leads to health problems ranging from mood disorders to diabetes. Sleep-deprived people may gain weight because their brains respond differently to high-calorie food and are at a risk of heart disease. People with disrupted rest due to sleep apnea show poor bone health. The medical group pointed out that brighter residential night time lighting is linked with reduced sleep, low sleep quality, sleepiness, impaired daytime functioning and obesity.
"Our study shows that the environmental light-dark cycle is important for health," says neuroscientist Johanna Meijer from Leiden University Medical Centre in the Netherlands. She added "We showed that the absence of environmental rhythms leads to severe disruption of a wide variety of health parameters." These included inflammatory response by immune system, muscle loss and osteoporosis. The premature aging and frailty in the mice can be traced to the light's harmful effect on their brains' circadian clock, according to the researchers.
The Study published in journal Current Biology
also said that the effects were reversible. After the mice were returned to a standard light and dark cycle for two weeks, their SCN neurons got back in normal rhythm, and their health problems improved.
It means that people experiencing prolonged light exposure - such as patients in intensive care or premature babies in neonatal units - can be helped by introducing periods of darkness. This could need extra measures like eye masks as even with eyes closed, light can pass through their eyelids and confuse their internal clock. The implications of this kind of research could mean that we need to monitor or regulate the way we use electric lighting and devices that provide artificial illumination as much as we keep an eye on other activities and substances that we think are detrimental to our health.