C for sight
As discussed earlier, a cataract occurs when protein in the eye’s lens clumps together, possibly in part due to the process of oxidation. Antioxidants such as vitamin C, vitamin E, and beta-carotene may help counteract this damage.
Vitamin C may be particularly important because this nutrient is concentrated in the lens of the eye much as lutein and zeaxanthin are concentrated in the macula. A number of studies have shown a link between relatively high intakes of vitamin C and a lower risk of developing cataracts. For example, researchers looking at a subset of women participating in the ongoing Nurses’ Health Study found that those women with intakes of vitamin C averaging about 350 mg a day were more than half as likely to develop two different types of cataracts compared to those with intakes below 140 mg a day. Women who took vitamin C supplements for 10 years or more also saw their risk of developing cataracts dip significantly compared to those who took supplements for a shorter period of time or not at all.
Again, knowledge is still evolving and it is too early for definitive recommendations. For example, both the timing and duration of vitamin C intake may be important. Cataracts usually develop over years and for vitamin C to be effective, intake may need to be high for a prolonged period.
However, there is no harm in consuming plenty of vitamin-C rich fruits and vegetables at any stage in life. While an intake of vitamin C of 350 mg such as that seen in the studies cited above is well above the current recommended dietary allowance for vitamin C of 75 mg per day for women and 90 mg per day for men, it is well below the tolerable upper intake level (the highest amount one can take before experiencing adverse health effects) of 2,000 mg per day. With careful choices, people who consume the recommended five to nine servings of fruits and vegetables a day can take in this amount through diet alone. Four ounces of orange juice, a cup of strawberries, a large kiwifruit, a cup of broccoli and a salad that includes a cup of romaine lettuce and 1/4 cup of red bell pepper, for example, provides more than 350 mg of vitamin C.
Vitamin C from supplements can also be included. Most multivitamin supplements contain at least 60 mg of vitamin C.
Fat and eye health
Scientists have also been scrutinizing the relationship between dietary fat and eye disease. Indeed, some scientists believe that the process of AMD is similar to that of cardiovascular disease; the same type of problem-causing plaques that form in the arteries leading to the heart may also form in the blood vessels in the eyes.
In one large survey of more than 110,000 volunteers, researchers found that people who consumed a high-fat diet were more likely to have AMD than those consuming a lower-fat diet. More than total dietary fat, what may be important is the type of fat and the ratio of one type of fat to another. Omega-3 fat, the kind found in fish, walnuts, almonds, and flaxseed, may decrease the risk of AMD. An increased risk of AMD may be linked to high intakes of certain fats found in some animal foods such as beef, pork, and lamb, and of the types of fat found in packaged baked goods and other commercially processed snack foods.
Scientists are still teasing out the nature of the fat–eye health relationship. Still, an overall low-fat diet that includes several servings of fatty fish each week and limits commercially processed baked goods and snack foods is likely to provide benefits. Even if the eyes aren’t helped, the heart certainly will be.
The Age-Related Eye Disease Study
Scientists have long been interested in whether supplemental doses of certain vitamins and minerals could affect the onset and progression of AMD and cataracts. Late in 2001, researchers released results from a large-scale, long-term study sponsored by the National Institutes of Health and known as the Age-Related Eye Disease Study (AREDS), which was designed to probe this relationship. Their evidence was compelling enough to cause the study authors to recommend a supplement formulation for people at high risk of developing advanced AMD.