DHA, EPA stave off age-related vision loss

Want to keep your eyesight sharp as you age? Eating lots of fish packed with healthy omega-3 fatty acids could help, new research suggests.

Among 1,837 people who had early signs of age-related macular degeneration (AMD), those with the highest consumption of omega-3 fatty acids were 30 percent less likely to progress to the advanced form of the disease over a 12-year period than those with the lowest omega-3 intake, researchers found.

Dr. John Paul SanGiovanni of the National Eye Institute at the National Institutes of Health in Bethesda, Maryland, and his colleagues report their findings in the December issue of the American Journal of Clinical Nutrition.

AMD is a deterioration of the retina that is the leading cause of vision loss among older US adults. About 1.75 million Americans and 3.35 million Europeans have AMD severe enough to impair their vision, according to the researchers.

While there are some drug treatments for the disease, they add, these medications have limited effectiveness, are expensive, and can lead to serious complications. Because inflammation is likely to be involved in AMD progression, and omega-3 fatty acids have anti-inflammatory effects, they add, these nutrients have the potential to help slow the progress of disease.

To investigate, SanGiovanni and his colleagues analyzed data from the Age-Related Eye Disease Study, a clinical trial run by the National Institutes of Health to investigate nutrition-based approaches to preventing and treating AMD. All of the study participants were free of advanced AMD in at least one eye, but did have some degree of earlier stage disease.

Over the course of 12 years, about 20 percent of people in the current study developed "dry" AMD, in which the tissue at the center of the retina disappears. Another 32 percent developed "wet" AMD, or neovascular AMD, in which abnormal blood vessels grow in the macula. People who consumed the largest amounts of the two main dietary types of omega-3 fatty acids -- docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) -- were about 30 percent less likely to develop either wet or dry AMD than people with the lowest intake, the researchers found.

Those who consumed the most DHA and EPA got about 11 percent of their calories from omega-3s, compared to about 1 percent for people with the lowest intake.

"Our results, if confirmed by other studies and extended by clinical trials, may guide the development of low-cost, easily implemented, and widely accepted interventions to prevent the progression to advanced AMD," SanGiovanni and his team conclude.

SOURCE: American Journal of Clinical Nutrition, December 2009

Dr. Cinque's comments: I'm not much of fish-eater, but I do take a fish oil supplement every day. For those that don't want to take fish oil, there is a DHA supplement derived from algae. But, it takes a lot of concentrating to get even 100 mgs DHA into a capsule, which makes it expensive. But, if you're determined not to consume fish in any way, shape, or form, then that is your best option.

What about flax you may wonder? Flax contains another, shorter omega 3, alpha linolenic acid (ALA). The body can convert the 18 carbon ALA to the 20 carbon EPA and the 22 carbon DHA by a process known as "desaturation and elongation." However, there is a lot of controversy about how reliable this process is. I take my cues from Dr. Bruce Holob of the Omega-3 Institute in Canada, and I don't think there is anyone who is more knowledgable about it than he is. Dr. Holob points out that the earliest studies about human conversion of ALA to EPA and DHA only date back to the 1990s. He says that it's clear that a "moderate" net rise in EPA from feeding ALA does take place- so long as the omega-6/omega-3 ratio is kept very low at 3:1 or lower (and very few do that in real life). However, the net rise in DHA from taking ALA is practically zero, and that is true across all fatty acid ratios. For example, even providing more than 10 grams a day of ALA from flax, brought about practically no rise in the amount of DHA in breast milk among lactating females.

Isotope studies conducted by the USDA in 1994 showed an ALA to DHA conversion rate of 4 percent, meaning that you would have to consume 25 grams of ALA to get 1 gram of DHA. But, that study, the best showing to date, has been criticized as faulty and has never been confirmed. Subsequent isotope studies have shown much less conversion, and in males, practically no conversion at all- less than .1 percent (Powlowski 2001, Hussein 2005). Why men have a much harder time converting ALA to DHA than women is unknown. But, the next time some self-styled nutrition expert tries to tell you that your body can make all the DHA it needs, and all you have to do is eat plenty of grains and beans and vegetables, just realize that that individual is grossly and dangerously misinformed..................
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