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The science of light therapy in a nutshell
Our understanding of the science of light therapy is very new and expanding rapidly. Cellular biologists, biochemists, histologists, biophysicists, psychologists and psychiatrists around the world are working to improve our knowledge. At the 2006 meeting of the Society for Light Treatment and Biorhythm Research (SLBTR) in Quebec over 34 papers were presented from all branches of science.
Light therapy first became an option for the treatment of seasonal onset depression (SAD) following the discovery in 1971 that very bright light could influence the control of the hormone melatonin. Melatonin is secreted by the pineal gland in the hypothalamus region of the brain. It is well documented that melatonin controls the body clock or circadian rhythm in mammals.
Melatonin production increases as light intensity falls and it is responsible for inducing sleep. The core body temperature is directly inverse to melatonin production and other physiological functions, alertness and vigilance are all directly related to the levels of melatonin in circulation.
Melatonin production is only suppressed by early morning sunlight and this action resets the body clock on a daily basis. Melatonin is produced from the feel good hormone serotonin and if there is no effective suppression of melatonin the subject experiences the combined effect of high melatonin and low serotonin with symptoms including depressed mood, lethargy, lack of energy, poor sleep patterns, loss of libido and carbohydrate craving.
2-5% of the population in northern latitudes experience clinical depression and meet the clinical definitions of Seasonal Affective Disorder. 40% of the population suffers sub-syndromal SAD usually defined as winter blues. There is growing evidence that the lack of bright morning light can also cause non-seasonal depression with all the attendant symptoms. Research in California confirmed that half the working population does not receive enough daylight to effectively suppress melatonin. A similar problem is experienced by the institutionalized eg the elderly, hospital in patients, prison populations etc.
Light deprivation symptoms are also experienced by those who live in conflict with their body clock such as night workers, shift workers and international travellers (jet lag). For physiological reasons the body clock is also shifted at two key life stages. It moves forward by 4 – 6 hours at puberty meaning that teenagers and students do not feel sleepy until the early hours and cannot wake before noon, with profound implications on their academic performance. Post-menopause and andropause the body clock shifts back leading to poor sleep patterns and a tendency to wake in the very early hours. Light therapy is proven to be effective in all these situations.
The mechanism of melatonin production and suppression has only been detailed over the last 4-5 years. The key receptors are non-image forming cells in the retina known as the intrinsically photoreceptive retinal ganglion cells (ipRGC).Unlike the rods and cones, these cells are scattered throughout the retina and occupy roughly 2% of the surface area of the retina. The ipRGC produce a protein called melanopsin. In addition to the control of melatonin production the ipRGC are responsible for the opening and closing of the iris in response to light intensity. In low light conditions the ipRGC send impulses along the optic nerve to an area of cells known as the Supra Chiasmatic Neurone (SCN) – this is the body clock. The SCN in turn controls the function of the pineal gland.
Research in the last year has confirmed that the SCN in man is just a small accumulation of specific neurons, but in mammals with pronounced circadian rhythms, such as rats, the SCN is a visible ovoid mass approximately 1/50th the size of the brain. Groundbreaking research in 2005/6 finally confirmed the biochemistry involved and discovered that it is extremely primitive and owes its action to processes found in invertebrate physiology.
Research in the last few years has also confirmed that melatonin suppression is under the control of very specific wavelengths of light. 460-470nm at the non-visible blue end of the spectrum activates the melanopsin in the ipRGC and green light at 540nm resets the receptor. Bright sunlight peaks at 470nm with a second smaller peak at 540nm suggesting that the primeval development of the process was very much determined by environmental factors.
These discoveries about the importance of specific wavelengths coincided with the discovery in 2001 of a method to produce a white light Light Emitting Diode (LED) which until that time had eluded science.
The white light LED produces light in a narrow range that peaks at 470nm with a second peak at 540nm, thus mimicking bright sunlight. White light LEDs produce next to no light in the yellow to red end of the visible spectrum. Furthermore, white light LEDs are totally free of ultra violet light and are therefore safe for long term therapeutic use.
It was soon discovered that white light LEDs were particularly effective in the suppression of melatonin and clinical trials have confirmed their effectiveness in the treatment of seasonal depression. The Litebook Company has secured worldwide patents for the use of white light LEDs for therapeutic purposes using ocular delivery methods.
Historically, SAD lights used daylight bulbs or fluorescent tubes to mimic daylight and had to achieve very high levels of intensity to have any therapeutic effect. The absolute minimum level of intensity is 3000 lux but SAD lights vie for position on the basis of intensity and lights of 10,000 lux or more are common. Unfortunately most of this light, and the energy to produce it, is wasted. A typical fluorescent SAD light would be the size of a small suitcase and use 85W of power. The Litebook elite is smaller than a paperback book, totally portable and operates off a rechargeable Lithium Ion battery producing 6W.
Lux is only an approximation of how we will perceive the intensity of a particular light source. For melatonin suppression, Lux appears to an inappropriate unit of measurement because it is the wavelength of the light not the intensity that is important. This is specifically demonstrated by the fact that most traditional devices emitting 10,000 Lux or more require a daily usage period of up to 2 hours, but The Litebook elite, with its 5000 Lux, achieves its objectives in just 15-30 minutes.
For more information and links to clinical trials visit www.litebook.com |
