image from Vista Eye Care
Dahunsi Ayomikun Nifemi (OD)
The health of the eye is reliant on the health of the body. There are about 50 known essential nutrients for the human body, which include the vitamins and about 20 minerals. Nutrition and the eye continues to be a field of very active research and the information available can be used as a guide for advising proper dietary habits and for considering vitamin and mineral supplements, rather than as firm recommendations. Some nutrients are likely to be toxic if taken in excess and so there is an upper limit for consumption that should not be exceeded.
Vitamins are today often referred to as micronutrients. Vitamin A is essential in the formation of the retinal photoreceptor pigments and vitamin A deficiency leads to defective night vision. Vitamin A is also important in maintaining the health of the ocular surface and keratomalacia occurs when the diet is grossly deficient in vitamin A. In common with vitamins C and E, vitamin A has anti-oxidant properties. Vitamin C is secreted into the aqueous humour where it is more concentrated than in other body fluids, suggesting its particular importance to the lens. The level of vitamin C in the aqueous increases with increased dietary intake, which suggests that the lens will feel the effects of increased vitamin C intake.
The development of cataract has been associated with a number of systemic diseases, including cardiovascular diabetic, renal and gastrointestinal (diarrhea), and with increased mortality. Similarly, hypertension is a risk factor for age-related retinal macular degeneration (ARMD). It is possible that vitamins and other nutrients may have a direct action in protecting the lens and retina, or separately in promoting the health of the body to benefit the eye indirectly. An extensive literature exists concerning the role of the anti-oxidant vitamins in the prevention of vascular disease.
It is likely that vitamin supplements given to populations with poor nutrition would have a Significant impact in preventing the development of cataract and that vitamin supplements given to persons with good nutrition would have a minor impact in preventing the development of cataract. It is also likely that vitamins would have a significant impact on those with good nutrition but at increased risk of cataract because of smoking. What is at present less certain is the effect of giving vitamin supplements to those persons already affected by cataract.
Other known vitamins have a role to play in eye health. Nicotinic acid (vitamin B3) and the other B vitamins (B1, B2, B6 and B12 are essential to the maintenance of optic nerve function. The effects of deficiency are not generally seen in Western populations, except in those taking excess alcohol or smoking excessively. The recommended daily allowance for adults is 1.4 mg of vitamin B1 (thiamine) and 1.6 mg of vitamin B2 (riboflavin).
The anti-oxidant vitamins A, C and E are present in green leaf foods, fruits, nuts and root vegetables. Pro vitamin A (beta-carotene) is present in dairy products, green plants and in yellow or orange fruits. Parsley and spinach are particularly rich sources and the best root vegetable for vitamin A is the carrot. Vitamin A is present in fruits, but fruits have a lower concentration than leaves.
About 20 different minerals are required for human health. Many of these are essential cofactors in enzymes catalyzing biochemical reactions providing the energy and synthetic capabilities upon which all life forms depend. These enzymes include those with anti-oxidant properties: glutathione peroxidase, superoxide dismutase and catalase. Only a sufficient intake of a mineral is required to satisfy all the available sites on the enzymes that need it, and it is unlikely that taking extra amounts of the mineral would have any further benefit.
Zinc plays a vital role in bringing vitamin A form the liver to the retina in order to produce melanin, a protective pigment in the eyes. Impaired vision, such as poor night vision and cloudy cataracts, has been linked to zinc deficiency. For natural dietary sources of zinc, try red meat, oysters and other shellfish, and nuts and seeds. When taking zinc, copper absorption is lessened. It’s recommended that zinc be combined with copper supplements. Essential fatty acids Omega-3 fatty acids are important for proper visual development and retinal function. Studies in pre-term and full term infants suggest that getting enough omega-3 fatty acids in the diet is essential for optimal visual development. Salmon, tuna and other cold water fish are the best sources of omega-3 fatty acids and can help reduce inflammation, enhance tear production and support the eye’s oily outer layer.
It’s believed that docosahexaenoic acid (DHA), a type of omega-3 fatty acid, helps in the development of retinal cells. It’s also thought to have a role in reducing inflammation and helping cells of the retina and the cornea heal and regenerate after damage due to light exposure and aging. Lutein and Zeaxanthin are carotenoids. Carotenoids are pigments found in plants and in your retina. Supplementing these pigments helps increase their density in your retina. They also absorb high-energy blue and ultraviolet light that can damage your eyes.
Proper nutrition can have preventive and protective mechanisms for people’s overall health‚ including ocular health. Pharmacologic doses of nutrients and supplements such as vitamins, minerals, and essential fatty acids can prevent or delay the onset of certain eye diseases. Eye care providers are perfectly positioned to identify, diagnose, and help prevent a multitude of health issues. They have the expertise to identify nutrition-related health issues and can consistently promote good nutrition.
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