The FDA has defined the term “dietary supplement” as a product that is intended to supplement the diet that contains one or more “dietary ingredients.” Vitamins, minerals, amino acids, herbs or other botanicals, dietary substances, concentrates, metabolites, extracts or combinations of the preceding types of ingredients are all examples of dietary ingredients.¹

The sale of dietary supplements is big business. In 2009, Americans spent approximately $26.7 billion on them.² Some supplement manufacturers claim that their products resolve difficult health problems such as obesity, arthritis and even vision loss. However, in most cases, few or no clinical trials have been completed to determine their safety or efficacy. That is because the FDA only provides guidelines for the production of dietary supplements—a sharp contrast to the strict regulatory process the FDA has created for the development and production of prescription and over-the-counter drugs.³ Although dietary supplement manufacturers must register their facilities, they are not required to register individual products with the FDA and do not need FDA approval to sell their supplement.⁴ The FDA can take action against manufacturers of any unsafe dietary supplement product after it is sold.

Manufacturers are permitted to advertise their supplement as a product that addresses nutrient deficiency, supports health or is linked to a particular body function if there is any research to support the claim. Any label claim must contain the following disclaimer: “This statement has not been evaluated by the US FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.”³ But, many people do not read fine print. The National Institutes of Health (NIH) agrees that the current level of FDA regulation is inadequate. According to a 2006 NIH consensus statement, “current level of public assurance of the safety and quality of multivitamins and minerals is inadequate, given the fact that manufacturers (of dietary supplements) are not required to report adverse events and the FDA has no regulatory authority to require labeling changes or to help inform the public of these issues and concerns.”⁵

Vitamins and Vision
According to a 2007 National Health Statistics Report survey of adults and children in the U.S., nonvitamin, nonmineral or natural product dietary supplements were the most popularly identified.6 These included the natural product supplements of echinacea, ginkgo biloba, ginseng, feverfew and garlic, as well as, animal cartilage extracts, amino acid products and enzyme supplements.⁶

Several natural product supplements that claim to improve vision are manufactured from plants and berries rich in pigments. People have long believed that the European huckleberry (or bilberry) enhances vision. In fact, during World War II, Royal Air Force pilots were fed bilberry to improve their night vision.⁷ But, unlike many other supplements, clinical studies were performed on bilberry extract to evaluate its effect on vision. In a placebo-controlled trial (N=15), patients received 160mg of bilberry extract (25% anthocyanosides) three times a day for 21 days. The results showed no difference in night visual acuity or contrast sensitivity between placebo and treatment groups.⁸

The xanthophyll pigment lutein, a dietary supplement typically derived from marigolds, is also said to promote vision. Lutein and zeaxanthin are the primary macular pigments within the human retina.⁹ In one controlled trial, 225 nonsmoking patients with retinitis pigmentosa (RP) were monitored over four years and showed improvement with lutein dosing.¹⁰ Patients received either a 12mg lutein tablet or a placebo tablet and 15,000IU of vitamin A palmitate per day. Results suggested that combined lutein and vitamin A treatment (vs. vitamin A-only) slowed the loss of midperipheral visual field in adults with RP.¹⁰

Despite mixed results, there is a continued interest in the use of bilberry and lutein for the prevention and treatment of cataracts, macular degeneration and vision loss.¹¹ The National Center for Complementary and Alternative Medicines (CAM) sponsors research on CAM therapies (such as bilberry and lutein) to determine whether they are safe and effective treatments and to establish possible mechanisms of action.¹²
Unlike the natural product supplements bilberry and lutein, the FDA provides guidelines on the daily intake of vitamins, minerals and essential fatty acids. While the FDA recommends that individuals get their recommended dietary allowances of essential nutrients from the foods they eat, vitamin and mineral supplements  are indicated for those with known deficiencies.

Vitamin A deficiency has been linked to vision loss in developing nations.¹³ Analysis of this causality has created a strong argument for the use of vitamins—particularly those with antioxidant properties such as vitamins A, E and C—to treat eye disease. For patients with intermediate risk of developing advanced age-related macular degeneration (AMD), a recent study by the Age-Related Eye Disease Study (AREDS) found that consuming high levels of antioxidant vitamins (vitamins C and E and the vitamin A precursor beta-carotene) and zinc reduced the risk of AMD by approximately 25%.¹⁴ Thus, commercially available AREDS vitamin formulations may provide ocular benefits to patients who are at high risk for developing advanced AMD.¹⁵ But please keep in mind that due to the associated risk of cancer, vitamin A/beta-carotene-containing supplements such as AREDS are contraindicated in smokers.⁵ The relationship between AMD and supplements containing lutein, zeaxanthin and omega-3 fatty acids will be evaluated in the next AREDS trial, AREDS2.¹⁵ Like you, we are very interested in the results of this trial and other clinical studies examining vision and the use of supplements.

Does “Natural” Mean “Good?”
Although dietary supplements are very popular, generally their use is not based on controlled clinical trials demonstrating product safety and efficacy. For this reason, eye care practitioners should take it upon themselves to remind their patients who take supplements that “natural product” does not necessarily mean “effective product.” 

Glossary of Terms

Complementary and Alternative Medicine (CAM): “complementary medicine” refers to use of CAM together with conventional medicine; “alternative medicine” refers to use of CAM in place of conventional medicine.  Nonvitamin, nonmineral and natural products: types of dietary supplements taken by mouth containing a dietary ingredient. Examples include herbs or herbal medicine, other botanical products such as soy or flax products and dietary substances such as enzymes. Antioxidant: an agent that inhibits oxidation, protecting cells from the damaging effects of reactive oxygen species (ROS) and other highly reactive chemicals such as free radicals. Vitamin: compounds that facilitate biochemical processes; only vitamin A, D and K are made in the body from precursor molecules while all other vitamins must be ingested regularly. Vitamin A is made from its biochemical precursor beta-carotene. Mineral: an inorganic element occurring in nature such as calcium and iron; essential minerals are excreted daily and must be replaced regularly.

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