|
Eat Well and Protect Your Eyes from Age-Related Diseases
By Wendy Priesnitz
Turns out mother was right when she told you to eat your carrots. There is growing evidence that the intake of certain foods and nutrients may help maintain eye health, a key quality-of-life concern for older persons.
In addition to vitamin A, for which a role in eyesight is well established, evidence suggests that vitamins C and E and the carotenoids lutein and zeaxanthin may be linked to a reduced risk for age-related eye diseases, in particular, age-related macular degeneration (AMD) and cataracts.
Cataract extractions are one the most common surgical procedures. Epidemiologists at the National Eye Institute in the United States have estimated that if the progression of cataracts could be delayed by ten years, the number of cataract extraction surgeries per year would be reduced by forty-five percent.
AMD is the leading cause of acquired blindness among the elderly. The exact cause of the breakdown of cells in the macula is not yet known; however, as with cataracts, the risk of AMD increases with age. Dry AMD can develop into the more severe wet AMD if blood vessels from the choroid begin to grow pathologically into the macula. Wet AMD can rapidly cause blindness due to the leakage of blood into the subretinal space. Laser treatments may retard or halt the process, but rarely can recover lost or damaged vision.
Vitamin C
There are logical reasons to suspect that vitamin C may play a role in eye health. First, the antioxidant properties of vitamin C may be particularly useful in protecting the lens. The lens and aqueous humor are isolated from the blood supply and contain few cells to provide repair mechanisms when oxidative damage occurs. Vitamin C is a small, water-soluble molecule that can penetrate the layers of the lens, providing the body with a means of delivering chemical protection into this isolated area.
Secondly, the active accumulation of vitamin C in the lens and aqueous humor is striking: Vitamin C concentrations are 20 times higher here than those found in plasma. Interestingly, vitamin C concentration correlates poorly with normal dietary intake. Only very high or very low vitamin C intakes appear to notably change the concentration in the lens.
Research has found consistent associations between higher dietary or plasma vitamin C levels and a reduced risk for cataracts, espeically among long-term smokers and people with hypertension. This implies that vitamin C may mitigate the impact of other cataract risk factors, rather than independently reducing cataract risk.
Length of usage also seems important. In one study, the need for cataract surgery was lower among women who used vitamin C supplements for ten years or longer, while a similar association between dietary intake alone and cataract risk was not found. In contrast, an association between vitamin C supplement use and cataracts has not been found in studies of shorter duration.
Vitamin E
Vitamin E is an essential nutrient for nervous system and reproductive function, as well as for antioxidant protection of all cell membranes. Unlike vitamin C, vitamin is not specifically concentrated in the eye as compared to other tissues.
Epidemiological studies have found a fairly consistent correlation between plasma vitamin E concentrations and cataract risk, whether reduced risk at high plasma concentrations, increased risk at low concentrations, or consistent risk associations across different populations.
One study found that vitamin E, along with other nutrients, helped some people who had moderate age-related macular degeneration, reducingd the risk of developing advanced age-related macular degeneration by 25 percent.
Lutein & Zeaxanthin
Carotenoids, the yellow to red pigments found in plants – including those carrots your mother encouraged you to eat for eye health – have long been of interest to the nutrition community because of the body’s ability to convert a few of these compounds into vitamin A.
Most of them have recently become more interesting to researchers due to their function as antioxidants, protecting cells from oxidative damage or potentially regulating cellular processes that monitor oxidation.
Two such compounds are lutein and zeaxanthin. They often occur together in the same food sources, and in many studies are reported together. Both lutein and zeaxanthin are associated with a reduced risk of both AMD and cataracts.
The eye concentrates these carotenoids in a layer of retinal tissue that comprises the macula region. Their biological function in the eye is not fully understood, but two potential functions have been proposed. One is based on the fact that lutein and zeaxanthin absorb near-to-UV blue light, the most damaging wavelength of light that actually reaches the retina. Secondly, lutein and zeaxanthin provide antioxidant defense against free radicals, and conditions in the macula are highly favourable for free radical formation.
In research studies where eyes were examined post-mortem from people who had AMD, it was found that these individuals’ eyes had significantly less lutein and zeaxanthin than those without AMD.
Increased macular pigment density has been demonstrated using spinach as a lutein-rich food and corn as a zeaxanthin-rich food, lutein dietary supplements, and bilberry extract as a low-dosage lutein supplement.
The link between lutein, zeaxanthin and AMD risk has been examined in two major studies. One study, which examined associations between nutrition and neovascular or “wet” AMD among people aged 55 to 80 found that AMD risk was significantly lower with increasing serum concentrations of lutein and zeaxanthin. Dietary intake of spinach or collard greens (which are particularly rich sources of lutein and zeaxanthin), was associated with lower AMD risk.
Recent research also indicates that easy-to-obtain levels of lutein and zeaxanthin intake can significantly lower risk of developing cataracts.
How Much?
Vitamin C: Whereas virtually everyone obtains the scant amount needed to prevent scurvy (10 to 15 mg), not as many people obtain the 200 mg needed to maximize levels in plasma and tissues, and thus provide optimum eye protection. Many researchers feel you should consume significantly more vitamin C. For example, 500 mg was the daily dose of vitamin C used in studies that showed a reduced risk of cataracts. One cup of fresh squeezed orange juice yields between 75 and 124 mg of vitamin C. Sweet red peppers will provide 283 mg per one cup serving, and a cup of broccoli yields 82 mg.
Vitamin E: Most people average 13 IU per day from their diet. A quarter cup of almonds will add just over that to your diet, while a bowl of cereal with wheat germ yields around 27 IU. The RDA for Vitamin E is 22.5 IU. Intakes as low as 100 to 200 IU have shown benefits to eye health. The American Optometric Association recommends 400 IU/day.
Lutein & Zeaxanthin: Epidemiological evidence indicates that approximately 6 mg per day are associated with reduced risk for AMD and cataracts. The American Optometric Association recommends 10 mg of lutein and 2 mg for zeaxanthin. A cup of raw kale yields 40 mg of lutein and zeaxanthin, while the same quantity of cooked spinach will add 7 mg. to your diet. Many of the same fruits and vegetables that are good sources of vitamin C are also good sources of lutein and/or zeaxanthin, such as spinach, orange peppers, tangerines, Brussels sprouts, and squash. Peas and corn are other good sources.
Wendy Priesnitz is Natural Life Magazine's editor, and the author of 13 books.
|
