It has long been known that vitamin A is necessary for vision. In fact, insufficient amounts of vitamin A can result in night blindness in adults and children whose diets lack vitamin A are at risk for destruction of the cornea ­ a common cause of blindness in developing countries. Recent research, however, indicates that vitamin A is not the only nutrient important to good eyesight. The Nursesą Health Study and the Health Professionals Follow-up Study has yielded new information on the relationship between diet and two common eye ailments - cataracts and macular degeneration.

Surprisingly, cataracts have become so common that cataract surgery is now a major contributor to the rising cost of health care. But, what exactly is a cataract? A cataract develops when the lens thickens to the point that it is no longer able to reflect light. Proteins coagulate into an opaque mass resembling something like an egg white, which prevents light from entering.

Another common but potentially more serious eye ailment is macular degeneration. The macula, located at the back of the eyeball, allows our eyes to focus on fine details. A mild form of macular degeneration may be a normal part of aging, but severe macular degeneration is now the most common cause of non-correctable blindness in the U.S.

Using data collected from the Nursesą Health Study and the Health Professionals Follow-Up Study, researchers have been able to track rates of cataract and macular degeneration. In the case of cataract, we looked at incidence of cataract extraction and also gathered information from ophthalmologists. To study macular degeneration, we included only people who had suffered a demonstrable loss of vision from this condition. Please see reference list at the end.

An analysis of these groups revealed a startling fact. After age, the first and most powerful predictor for the development of cataracts and macular degeneration was not related to diet at all - in fact - it was cigarette smoking. Smokers who smoked 25 cigarettes per day ­ the equivalent of one pack - had approximately 2.5 times higher risk of developing cataracts or diminished vision due to macular degeneration than those who did not smoke. Unfortunately, the risk of developing cataracts remains even after quitting.

So, how do dietary factors affect vision? Beyond the well-known vitamin A are there other nutrients that can offer protection against eye disease? Based on the researchers findings, carotenoids such as alpha and beta carotene and lycopene proved only marginally helpful in reducing risk of cataract. The exception was a type of carotenoid called lutein (and a closely related compound, zeaxanthin) found in leafy green vegetables such as kale, spinach and broccoli. In fact, lutein consumption appeared to lower risk by as much as 20% in two separate studies among men and women. Also, in a related analysis conducted by our colleague, Dr. Johanna Seddon, higher consumption of lutein was associated with lower risk of macular degeneration. How might it work? Lutein is concentrated in the retina and the macula and absorbs the blue part of the light spectrum; there it may lessen the effects of oxidative stress at the back of the eye. Also, lutein is the only carotenoid found in the lens, where it may perform a similar antioxidant function.

What can we do to reduce the risk of developing cataracts or macular degeneration? First of all, stop smoking ­ even sufficient amounts of lutein in the diet failed to protect smokers. Otherwise, eat plenty of leafy greens such as kale, spinach, broccoli and, of course, carrots. While the studies I have described will need further confirmation, including greens in our daily diet is prudent and will be an excellent source of many micro nutrients. How much is plenty? About one or one-half servings per day appears to be desirable. Interestingly, cooked spinach or other greens ­ with a little olive oil and vinegar - is preferable to raw spinach. As anyone who has cooked spinach knows, a large amount quickly boils down to a more modest portion. Thus, by cooking the spinach you are actually getting more spinach and also more lutein. This is because the process of cooking breaks down the cell structure while the oil aids in absorption.

Why are these findings important? In the past it was thought that not much that could be done to prevent eye disease. The findings from the Nursesą Health Study and the Health Professionals Follow-Up Study make it clear that there are things that we can do, such as eating leafy greens, protecting our eyes from the sun, and, of course, not smoking. And, this could be only the beginning - it is likely that researchers will continue to uncover other dietary and lifestyle factors that affect eyesight.

REFERENCES

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