With North Americans spending billions of dollars each year on nutritional supplements, researchers have analyzed popular eye vitamins to determine whether their formulations and claims are consistent with scientific findings. The findings: some of the top-selling products do not contain identical ingredient dosages to eye vitamin formulas proven effective in clinical trials. What’s more, claims made on the products' promotional materials lack scientific evidence.
The leading cause of blindness among older adults is age-related macular degeneration (AMD), a chronic disease that attacks the central part of the retina called the macula, which controls fine, detailed vision. The condition results in progressive loss of visual sharpness making it difficult to drive a car, read a book and recognize faces.
The exact cause of AMD is unclear, but factors such as genetics, family history, cigarette smoking, high blood pressure, excessive sunlight exposure, and a diet low in antioxidants are linked with a greater risk.
Recommended treatment for AMD at certain stages of the disease includes nutritional supplements. The landmark Age-Related Eye Disease Study (AREDS), published in 2001, found that a specific supplement formula containing high doses of antioxidants and zinc could slow the worsening of AMD in those who have intermediate AMD and those with advanced AMD in only one eye.
A follow-up study that concluded in 2011, called AREDS2, determined that the formula was still effective if one ingredient, beta-carotene (a form of vitamin A), was replaced with related nutrients, lutein and zeaxanthin. Beta-carotene was substituted in AREDS2 due to its link to increased risk of lung cancer in smokers. The two studies prompted a surge in sales of eye supplements marketed as containing the AREDS or AREDS2 formulas.
To test whether the products are consistent with the studies' findings, researchers compared the ingredients in top-selling brands to the exact formulas proven effective by AREDS and AREDS2. The researchers - based at Yale-New Haven Hospital-Waterbury Hospital, Penn State College of Medicine, Providence VA Medical Center and Warren Alpert Medical School of Brown University - identified the five top-selling brands based on market research collected from June 2011 to June 2012, and analyzed the brands' 11 products.
They found that, while all of the products studied contained the ingredients from the AREDS or AREDS2 formulas:
- Only four of the products had equivalent doses of AREDS or AREDS2 ingredients
- Another four of the products contained lower doses of all the AREDS or AREDS2 ingredients
- Four of the products also included additional vitamins, minerals and herbal extracts that are not part of the AREDS or AREDS2 formulas
In addition, while all 11 of the products' promotional materials contained claims that the supplements "support," "protect," "help" or "promote" vision and eye health, none had statements specifying that nutritional supplements have only been proven effective in people with specific stages of AMD. There were also no statements clarifying that currently there is not sufficient evidence to support the routine use of nutritional supplements for primary prevention of eye diseases such as AMD and cataracts.
"With so many vitamins out there claiming to support eye health, it's very easy for patients to be misled into buying supplements that may not bring about the desired results," said first author Jennifer J. Yong, M.D. "Our findings underscore the importance of ophthalmologists educating patients that they should only take the proven combination of nutrients and doses for AMD according to guidelines established by AREDS and AREDS2. It's also crucial that physicians remind patients that, at this time, vitamins have yet to be proven clinically effective in preventing the onset of eye diseases such as cataracts and AMD."
A results table of the analyzed products can be found at http://www.aao.org/newsroom/release/upload/Table-1-OcularNutritionalSupplements-InPress.pdf (PDF file).
The American Academy of Ophthalmology recommends ophthalmologists consider antioxidant vitamin and mineral supplementation, per the AREDS and AREDS2 trials, for patients with intermediate or advanced AMD. It also maintains that, based on the six-year timeframe of the AREDS trial, there is no evidence to support the use of these supplements for patients who have less than intermediate AMD.
Source: Ophthalmology, 2014.
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