Mar 10, 2015

What Everyone with a Retinal Disease Should Know about Vitamin A

Science Education

In the retina, vitamin A is an essential ingredient in the complex biochemical process that makes vision possible.

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Photo of a woman's eye.

If you think of your retinas as the engines that power your vision, then vitamin A is their fuel. Without vitamin A in our diets, we wouldn’t see.

In developed countries, typical diets provide enough of the nutrient for good vision and general health. However, according to the World Health Organization, Vitamin A deficiency is a public health problem in more than half of all countries, especially in Africa and Southeast Asia, impacting young children and pregnant women in low-income areas the most. As many as 500,000 vitamin A-deficient children become blind every year.

In the retina, vitamin A is an essential ingredient in the complex biochemical process that makes vision possible. Known as the visual cycle, the process involves the conversion of light into electrical signals, which are sent to the brain, where they’re formed into images.

It begins when proteins called opsins are made light-sensitive by metabolized vitamin A in the retina’s photoreceptors. When light hits the back of the eye and is absorbed by the opsins, they trigger the formation of electrical signals.

Vitamin A Palmitate as a Potential Therapy for Retinitis Pigmentosa
Eliot Berson, M.D., at Massachusetts Eye and Ear Infirmary (MEEI), Harvard Medical School, conducted Foundation-funded clinical studies of vitamin A palmitate as a therapy for retinitis pigmentosa (RP). He found that it slowed vision loss, and its effect was enhanced when combined with docosahexaenoic acid (DHA), a healthy fat abundant in coldwater fish, such as tuna and salmon, and the antioxidant lutein. Dr. Berson used a vegetarian DHA supplement in his studies.

There are important considerations to be made before embarking on vitamin A palmitate therapy. First, do not take the high level of vitamin A palmitate (15,000 IUs) recommended by Dr. Berson without doctor supervision. It can be toxic to the liver, and a test should be performed on a regular basis to ensure that it isn’t.

Second, Dr. Berson evaluated the nutrient for only RP and some forms of Usher syndrome (RP with hearing loss). Vitamin A palmitate should not be taken for a retinal disease that was not part of his study.

Before supplementing with vitamin A palmitate, I recommend that you read the Foundation’s Vitamin A Packet to learn about the diseases included in the study, as well as many other important considerations and caveats.

Determining Who Might Benefit Most from Vitamin A Palmitate Therapy
One of the big challenges in identifying therapies for RP and Usher syndrome is they’re actually a family of diseases. Collectively, mutations in more than 60 genes can cause the conditions. So, in essence, more than 60 diseases fall under the RP-Usher umbrella.

Because each gene plays a different role in the retina, when they’re defective, they cause vision loss in different ways. While some emerging treatments are cross-cutting and may work independent of the genetic defects, many only target specific genetic defects and disease pathways.

While Dr. Berson’s study group as a whole had their vision loss slowed by the therapeutic regimen, only some patients benefitted, and it wasn’t clear if genetic profiles were a factor. Most of the patients in Dr. Berson’s studies did not have their disease-causing gene mutation indentified when they enrolled.

To determine if certain genetic profiles benefitted more than others, the Foundation is funding Eric Pierce, M.D., Ph.D., at MEEI, to genetically test some of the participants to see if there is any correlation between their mutations and changes in vision.

He’s also studying reduced doses of vitamin A palmitate in children to determine if they can achieve benefits similar to those in adults.

Vitamin A is Harmful for People with Inherited Macular Diseases
Do not take any vitamin A supplement if you have Stargardt diseaseBest diseasecone-rod dystrophy or any other form of an inherited macular degeneration. These conditions result from the accumulation of toxic waste products from the processing of vitamin A. In animal studies, vitamin A supplementation led to more waste and accelerated vision loss.

For age-related macular degeneration, a supplement evaluated in the Age-Related Eye Disease Study (AREDS) is often prescribed to reduce risk of vision loss. The original formula had beta carotene, a form of vitamin A, but in the updated formula, AREDS2, it has been replaced by lutein and zeaxanthin. That’s because beta carotene increases risk of lung cancer in current and former smokers.

An Important Reminder
Do not take vitamin A without doctor supervision and reading the Foundation’s Vitamin A Packet.