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Researchers continue to find nutrition’s value in preventing — even treating — AMD
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HAMPSTEAD, N.C. — As research continues to reinforce the connection between nutrition and age-related macular degeneration (AMD), investigators are better understanding these nutrients and how they interact.
Of major interest in recent nutritional studies, said Edward Paul, OD, PhD, clinical director at Atlantic Eye Associates here, is “ground-shaking” information about the carotenoid lutein “that will really turn the way we look at nutrition on its ear.” In a yet-unpublished study, he said, lutein, which “is the new ‘buzz’ nutrient for treating macular degeneration, is found to actually compete with vitamin A in the small intestine for the same absorption receptor site.”
Competition may reduce absorption
What that means, said Dr. Paul, whose PhD is in nutritional medicine, is that for patients taking multivitamins with lutein, “We don’t really know how much lutein is being absorbed because vitamin A is competing for the same receptor site and is possibly robbing the patient of absorption.”
This study, he said, represents a “huge paradigm shift when you consider that we had been recommending lutein be combined with other antioxidants, which is a reasonable thing to recommend. But when these two nutrients are competing for the same receptor site, they’re neutralizing one another.”
He said that these two nutrients do not completely cancel each other, but “we do know from sound science that there will be reduced absorption of one or the other, and we believe that lutein is probably the one that will be the least absorbed.”
While Dr. Paul hopes this information will change what clinicians recommend in practice, this is not to downplay the importance of lutein. Robert Abel Jr., MD, clinical professor of ophthalmology at Thomas Jefferson University in Philadelphia and author of the Eye Care Revolution, said of all nutrients, lutein is the most well researched as far as its beneficial effects on the eye: “There is truly more information on lutein, regarding both its preventive and therapeutic effects for AMD.”
Lutein still key nutrient
Researchers are now engaging in the kind of long-term studies that will further solidify lutein’s place as a key nutrient for AMD, and the evidence continues to build, said Dr. Abel, who is on the Lutein Information Bureau’s advisory board. Recent studies have shown the carotenoid is effective not only for prevention of AMD but for therapy and improved contrast sensitivity; that it can help seniors attain contrast sensitivity similar to healthy adults aged 24 to 36; and that lutein and zeaxanthin levels inversely correlate with the risk for macular degeneration.
Lutein, Dr. Abel added, has been shown to be effective in the 445-nm wavelength, which is where the most sensitive and least numerous blue cones reside. “This is exactly where the lutein is deposited,” he said. “There’s a strong indication that this is an important carotenoid, especially because beta-carotene does not have a great presence in the retina.”
Although lutein and vitamin A appear to compete, Dr. Paul said in his practice he recommends that patients take lutein in a separate supplement at a different time of day than their normal nutritional supplements. “So I’m still having them take some kind of antioxidant or multivitamin or multimineral supplement, but then I’ll have them take, at a different time of day, the lutein. That way, we can be assured of optimal absorption.”
Dr. Paul recommends patients take a minimum of 12 mg of lutein per day “for it to be clinically effective.” In terms of diet, he added, that is the same as eating four large salad bowls of spinach each day.
Dr. Abel recommends patients with wet or dry AMD take 6 mg of lutein for several months and then 2 mg daily after that. “You can actually intervene with the dry form,” he said. Dr. Abel added that the problem with eating massive amounts of spinach is that oxylates can increase the risk of kidney stones, and vitamin K may interfere with anti-coagulation medications.
Patients should take DHA
Another nutrient that has become more prominent regarding eye health, Dr. Paul said, is the omega-3 fatty acid DHA, which is found primarily in oily fish such as tuna, mackerel and salmon. These fish are heart-healthy, Dr. Abel added, because they eat algae.
A recent New England Journal of Medicine study showed that people who had eaten canned tuna three times a week had an almost miraculous stabilization and — sometimes — even improvement in their visual acuity, Dr. Paul said, and the DHA in the tuna was responsible for this. DHA has already been deemed critical for good heart health and is recommended by cardiologists for patients with hypertension, Dr. Paul said, and “we now know it’s critical for retinal health, specifically macular health.”
DHA helps support cell membranes, Dr. Abel said. The eye’s receptors consist of at least 30% DHA, he said, and light stresses them, causing them to break down and build up. Dr. Abel said people should eat right, get plenty of sleep and be wary of antacids, which stop acid production “and decrease your metabolism of food right from the beginning of the cycle.”
Dr. Paul now tells his AMD patients that not only do they need to take a good antioxidant and a separate lutein supplement, but they also need to take 500 mg of DHA per day.
“We’ve known for years that DHA was good for neural health and eye health,” Dr. Paul said, pointing out that in Britain all baby formulas have DHA supplemented because it is known to be critical for neural development.
Several bioflavonoids also important
Practitioners should also recommend that patients take several bioflavonoids, including bilberry, grape seed extract and gingko biloba. Bioflavonoids, Dr. Abel said, strengthen capillaries by cross-linking collagen, and bilberry supposedly improves night vision.
“What is so critical about these is that bioflavonoids by and large have a much higher potency than some of the vitamin and mineral antioxidants by themselves when you talk about antioxidant activity,” Dr. Paul said. For example, he pointed out that grape seed extract is 60 times more potent per milligram than vitamin E: “You get more bang for your buck.”
Also, Dr. Paul said that bioflavonoids have been found to have a synergistic effect with vitamin C, boosting vitamin C absorption by 50%. So, he said “the take-home pearl” is that anyone taking vitamin C should be taking vitamin C with bioflavonoids.
While glutathione is instrumental in good retinal health, Dr. Paul said, there has not been a great deal of new research about its effect on the eye. “It’s a necessary nutrient, but so is vitamin B12,” he said.
However, glutathione is one of the most important antioxidants in the body, Dr. Abel said. “We essentially get it from anything that has protein in it.”
Nutrition no longer unappreciated
In general, the value of vitamins is now well recognized by eye care practitioners. For years, Dr. Paul said, traditional medicine, optometry and other health professions said “if you want to take vitamins, fine, but they’re probably not doing you all that much good. We know now that it is not a fact and everybody needs nutritional supplementation.”
However, he said optometry school and medical school educations are not addressing this adequately: “I’m finding that practitioners are absolutely starving for the proper information to tell their patients,” Dr. Paul said. “And what’s happening in many cases is that the patient is better educated than the doctor is.”
Dr. Abel agreed, saying, “Patients can be your best source of information.”
Dr. Paul said when he first began lecturing on nutrition a few years ago he would get small audiences of about 30 people, but now his lectures are packed and are among the most popular sessions at many conferences.
Dr. Abel acknowledged that the field is “creeping along,” and said the AREDS (Age-Related Eye Disease Study), a 4,600-patient study of nutrients and their effect on eye disease, may show that certain nutrients are significantly better than placebo, and, if so, “It will change the way eye care professionals think.”
Nutritional research is still enigmatic and difficult, Dr. Abel said: “It is a bottomless pit. The secrets of nature are only slowly being revealed.”
And Dr. Paul added, “We may only understand 1% of what is truly taking place at the molecular and absorption level. We’re still kind of throwing darts in the dark.”
The work in nutrition is so difficult because nutrients have — as the lutein-vitamin A relationship demonstrates — often surprising circumstantial effects on each other. For instance, Dr. Abel said too much zinc suppresses copper; beta-carotene and lutein compete; and fat-soluble items such as DHA, lutein and vitamins A and E must be taken with a meal.
“It’s important to step back and realize that you’re not just firing a single bullet,” Dr. Abel said, “but you’re looking for harmonious management, either as prevention, maintenance or therapy.
“I think we have a long way to go in discovering what works,” he continued. “I think we also cannot use one supplement to the exclusion of another.”
For Your Information:
- Edward Paul, OD, PhD, can be reached at PO Box 1200, Hwy 17 North, Hampstead, NC 28443; (910) 270-2800; fax: (910) 270-9100. Dr. Paul has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Robert Abel Jr., MD, can be reached at Delaware Ophthalmology Consultants, Concord Plaza, 3501 Silverside Rd., Naamans Bldg., Wilmington, DE 19810; (310) 477-2600; fax: (302) 477-2650. Dr. Abel has no direct financial interest for the products mentioned in this article. He is a paid consultant for Kemin Foods as chairman of the Lutein Information Bureau Advisory Board. He is also a paid consultant for Martek Biosciences, which distributes DHA.