14 July 2017
Blue light is part of the visible light spectrum. It is present in sunlight, which also contains invisible ultraviolet rays (which we all know about because they tan or burn the skin) but the visible part is made up of red, orange, yellow, green and blue light and many shades in between of these colours depending on the energy and wavelength of the individual rays. Combined, this spectrum forms the "white light" part of sunlight.
Throughout our lifetime our eyes are exposed to a variety of visible and invisible light, not just from natural sunlight where most blue light exposure comes from, but from the perpetual presence of electric lights in our homes, fluorescent and LED lights in offices, our flat screen television and computer screens, mobile phones and other digital devices as well.
Blue light rays have the shortest wavelength (ranging from 380 to 510 nm) and the highest energy in the visible spectrum and because they scatter so readily in the atmosphere when they collide with water particles they confer that wonderful blue colour to the sky on a sunny summers day.
Unfortunately, however, the human eye lacks the ability to withstand penetration of visible blue light, which passes right through the cornea and lens to reach the retina. Over the course of time this can promote lasting damage to the light sensitive cells in the retina and can lead to changes identical to those of macular degeneration, one of the main causes of permanent visual loss.
This risk is considered to become even greater amongst the thousands of people undergoing cataract surgery because clouding of the ageing lens means that some blue light rays are filtered out and without it, after the surgery, the retina may become more vulnerable. (1) Cataracts and AMD are among the leading cause of visual loss and acquired blindness in the US and UK affecting the quality of life of millions of people. (2) Usually starting in people over 50 an estimated one in every 10 people over 65 develop signs of AMD. Whilst age, family history, smoking, ethnicity and nutrition may all contribute to it, a lifetime's exposure to lots of sunlight undoubtedly plays an important role. The light sensitive cells in the macula where incoming rays of light are most sharply focused, begin to break down causing central vision to deteriorate. This visual loss is usually gradual although occasionally rapid but the result is difficulty in reading, distortion of images, colours appearing less vibrant and people's faces becoming harder or impossible to recognize.
The challenge – blue light is necessary and to some extent desirable. There is good evidence for example that high-energy visible light enhances alertness, cognitive function and mood. (3-5) It forms a significant part of the diffused white light emitted by therapeutic light boxes used in the treatment of seasonal affective disorder, for example. The trick therefore is to enjoy its benefits but at the same time to minimize the damage it causes to the back of the eye. Therefore, attention has turned in recent years to good nutrition and in particular to the important role of lutein and zeaxanthin in helping to support eye health. (6-9)
Lutein and zeaxanthin are just two of several hundred carotenoids found in nature, in vegetables, fruit and in many other plants many of which have important antioxidant properties. This means they protect the body from harmful unstable free radicals responsible for inflammation. But unlike other carotenoids only lutein and zeaxanthin are found in high quantities in the macula, giving it its yellowish color. The depth of this color can be measured as macular pigment optical density (MPOD), which has recently become a useful biomarker for predicting disease and visual function. There is plenty of epidemiological evidence that the amount of macular pigment is inversely associated with the incidence of AMD. (10).
In nature, lutein and zeaxanthin absorb excess sunlight to prevent damage to plants especially from high-energy visible blue light. In the retina, lutein and zeaxanthin block passage of blue light to the retina thereby reducing light- induced oxidative damage forming the basis of the suggestion that higher intakes of these antioxidants may help to slow the progression of AMD. (11) Several studies appear to support this hypothesis showing that supplementation with lutein and zeaxanthin among other carotenoids, with or without long-chain polyunsaturated fatty acids (LCPUFAs), can increase MPOD, visual acuity and contrast sensitivity in patients with early AMD. (12,13,14)
With an increasingly aging population healthy enough to benefit from all of their senses and especially their eyesight, oral supplementation with lutein and zeaxanthin as an insurance policy for good visual acuity seems a wise choice. There are no reports of any toxic side-effects in the literature and while there is no current recommended daily intake, a general consensus is that 10 mg and 2 mg a day of lutein and zeaxanthin respectively is suitable especially for those with a low dietary intake of fruit and vegetables.
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