According to "Foundations of Cellular Neurophysiology," the human visual system requires about 30 percent of the body's oxygen and about 25 percent of its nutrient intake to function properly. Nutrient-deficient diets and inactive lifestyles contribute to eye diseases in the United States, where the National Eye Institute estimates 9 million adults beyond the age of 40 suffer from macular degeneration and 20 million have cataracts. Vitamins A, C and E can reduce the incidence of these eye diseases and contribute to better vision.
Vitamin A
Vitamin A is an essential nutrient for the functioning of the human visual system. According to the book, "The Vitamins," vitamin A is utilized in the formation and maintenance of the delicate surface lining of the eye and eye lid, which provides a moist barrier against harmful debris, bacteria, viruses and other microorganisms. In addition, the surface lining provides lubrication necessary for blinking, which occurs about 10 million times per year. Prolonged vitamin A deficiency leads to xeropthalmia, or dry eye, which causes corneal damage, ulcers, scarring, and potentially, blindness.
Vitamin A, as retinol, is also essential for the synthesis of rhodopsin, which is a light-sensitive visual pigment in the retina needed for visual acuity in darkness. With the use of rhodopsin, humans can detect about 500 shades of gray in dark conditions. One of the early symptoms of acute vitamin A deficiency is impaired darkness adaptation, commonly called night blindness.
Vitamin C
The National Eye Institute notes that macular degeneration and cataracts are considered common eye diseases in the United States and are leading causes of impaired vision throughout the world. Both diseases occur more frequently and severely with advancing age, especially in economically disadvantaged areas, so it is theorized that cumulative oxidation damage and nutritional deficiencies are important causal factors.
Vitamin C, because of its powerful antioxidant properties and role in blood vessel and tissue integrity, has been investigated for its effect on eye diseases. A study reported in a 1999 edition of the "Journal of Clinical Epidemiology" reported that high blood levels of ascorbic acid, or vitamin C, was correlated to reduced incidence of cataract formation in older Americans, and the researchers concluded that vitamin C may be of importance for the prevention of cataracts. In addition, dietary vitamin C was also found to slow progression of macular degeneration.
Vitamin E
Vitamin E also displays powerful antioxidant properties and has also proven beneficial in preventing certain eye diseases. The National Institutes of Health states that there are several studies that show vitamin E reduces risk and slows progression of macular degeneration and cataract formation, as well increases lens clarity, but other studies that report conflicting data, so overall, firm conclusions about vitamin E effectiveness are difficult to establish. Vitamin E is proven, however, to promote blood vessel integrity and blood flow by reducing platelet cell aggregation, which are important for the small arteries being able to deliver oxygen and nutrients to the retina and other structures of the eye.
References
- "Foundations of Cellular Neurophysiology;" Daniel Johnston and Samuel Miao-Sin Wu; 1994
- National Eye Institute, National Institutes of Health: Summary of Eye Disease Data
- "The Vitamins, Third Edition;" Gerald F. Combs; 2007
- "Journal of Clinical Epidemiology"; Serum Ascorbic Acid and Other Correlates of Self-reported Cataracts Among Older Americans; J.A. Simon; December, 1999
- National Institutes of Health, Office of Dietary Supplements: Vitamin E and Eye Disorders
