DEAR DOCTOR: Can lutein really help prevent, or treat, macular degeneration?
DEAR READER: Age-related macular degeneration, or AMD, is the leading cause of irreversible blindness in the elderly. It's a progressive disease affecting the macula, the central portion of the retina involved with central vision. Changes linked to AMD generally begin after the age of 40, and estimates suggest that approximately 50 million people worldwide suffer from some form of AMD. Further, rates of people with late stages of AMD are increasing.
Research has long suggested that diets high in lutein -- an antioxidant related to beta-carotene and vitamin A -- could reduce the risk of the disease. Like its better-known cousins, lutein is one of nearly 700 organic pigments called carotenoids that absorb light energy and act as antioxidants in plants, bacteria, fungi and algae. A special characteristic of lutein -- and of another carotenoid, zeaxanthin -- is that they accumulate in the retina of the eye and help form retinal macular pigment. This pigment absorbs damaging blue and near-ultraviolet light and thus protects the macula from light injury. In addition, these carotenoids' antioxidant effects help protect the eye from various types of damage.
A typical American diet contains 1 to 2 daily milligrams of lutein. It's found in high amounts in spinach, kale, parsley and romaine lettuce. It is found in lesser amounts in pistachios, asparagus, broccoli, green beans and eggs. One interesting aspect of eggs is that the fat content of eggs allows for better absorption of both lutein and zeaxanthin. Also, cooking oils and oils in salad dressing can increase the absorption of dietary lutein and zeaxanthin.
A 2012 analysis of six studies evaluated whether diets high in lutein and zeaxanthin had any effect on macular degeneration. The participants in the studies were followed from five to 18 years. None of the studies found any impact on the early changes associated with macular degeneration. However, the four studies that assessed impact on more advanced macular degeneration showed a 26 percent reduction among people with the highest dietary intake of lutein and zeaxanthin compared to those with the lowest intake.
The evidence for supplement use is less clear. One study, known as AREDS2, assessed the impact of 10 milligrams of lutein and 2 milligrams of zeaxanthin in supplement form among 4,203 adults over the age of 50 who already had the beginning stages of macular degeneration. After five years, those who took lutein and zeaxanthin had a 10 percent reduction in the rate of advanced AMD. Note that the study didn't include those without macular degeneration.
It's clear that lutein is helpful in the diet, but in regard to the prevention of macular degeneration, there is thus far insufficient evidence that taking a lutein supplement makes a difference for most people.
If you have been diagnosed with AMD or have a genetic susceptibility to the disease, you should certainly boost your dietary intake of lutein and zeaxanthin by increasing the amount of spinach, kale, lettuce and eggs in your diet. You should also exercise regularly and, of course, not smoke.
If you already have the early stages of macular degeneration, you should not only increase your dietary intake, you should consider supplements of both lutein and zeaxanthin.
(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)
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