All life evolved with the electromagnetic frequencies from the sun and the earth, and these frequencies are considered essential to all life. Life itself synchronizes and harmonizes with these frequencies. But what happens when these frequencies are disrupted by modern technology?
With the growing use of energy saving lamps and the development of new lighting technologies, comes the long-term concern that some people who have conditions that react to light might be negatively affected by this shift.
Previous research by Northwestern scientists showed that people who received the majority of their bright light in the morning weighed less than those who were exposed to most of their bright light after 12 p.m. The researchers wanted to understand why. Mouse studies also have shown that mice kept in constant light have altered glucose metabolism and gain weight compared to control mice.
"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. But there was some more encouraging news, too.
"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.
Strikingly, the disruption to normal light and dark patterns and the circadian rhythm led to a reduction in the animals' skeletal muscle function as measured in standard tests of strength. Their bones showed signs of deterioration, and the animals entered a pro-inflammatory state normally observed only in the presence of pathogens or other harmful stimuli. After the mice were returned to a standard light-dark cycle for 2 weeks, the SCN neurons rapidly recovered their normal rhythm, and the animals' health problems were reversed.
The findings suggest that more care should be taken in considering the amount of light exposure people get, particularly those who are aging or otherwise vulnerable. That's important given that 75 percent of the world's population is exposed to light during the night. Constant light exposure is very common in nursing homes and intensive care units, and many people also work into the night.
"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."
They say they now plan to perform more in-depth analysis of the influence of distorted light-dark cycles on the immune system. They'd also like to investigate possible health benefits to patients exposed to more normal conditions of light and dark.
There are two groups of patients who react abnormally to light: those whose diseases are induced by UV/IR or visible light (the photodermatoses) and those who have a pre-existing skin condition which is made worse by light.
The part of the spectrum that plays the main role is UV light, so the main concern is with light sources that emit UV, such as CFLs. The severity of these diseases varies widely between patients and the amount of UV required to produce symptoms is also variable:
- Polymorphic light eruption (PLE): Usually affects females and flares up in spring or early summer and results in an itchy, red, spotty rash on skin exposed to sunlight. For most patients, artificial light sources do not induce this disease.
- Chronic actinic dermatitis (CAD): This affects males over 50 years of age and results in sensitivity to various allergens, to UVA, UVB and also visible light for some patients. UV from artificial light could induce the disease in people with moderate or severe CAD.
- Actinic prurigo (AP): This uncommon disease happens all year round but is particularly bad in spring and summer. Skin exposed to sunlight develops itchy, red and inflamed bumps. Severe cases may be at risk from CFLs or other UV-emitting sources.
- Solar urticaria: This skin disorder affects both males and females and if it develops into a generalized urticaria, it can result in anaphylactic shock, so it can be fatal. Severely affected patients may be at risk from CFLs and unfiltered halogen sources producing UV/visible radiation.
- Hydroa vaccineforme: This is a rare disease that affects both sexes and produces blisters and scarring on skin exposed to sunlight. Low energy artificial light sources that emit UVA, can affect some patients.
- Lupus erythematosus (LE): This affects all age groups in both sexes and arises in people who produce antibodies against the breakdown products of their own cells so patients are susceptible to agents that cause cell death. Some drugs and factors such as UV (mainly UVB) exposure can induce this disease. At least some patients are at risk from long-term exposure to UV from CFLs and unfiltered halogen lamps.
- Porphyrias are a rare group of diseases that are inherited but are also induced by environmental factors and all relate to the accumulation of the photosensitive pigment porphyrin within the skin. Artificial light sources, including incandescent bulbs, can cause skin reactions and even burns in the most sensitive patients.