Vitamin A (Vitamin A Palmitate)
see also Beta-carotene, Rhodopsin: Vitamin A is found in certain animal and milk products, fruits and vegetables (and as a commercial supplement) that is used as part of a nutritional treatment of RP.
Vitamin A actually refers to a family of similarly shaped molecules: the retinoids. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate (vitamin A palmitate), which is converted to an alcohol (retinol) in the small intestine. Vitamin A can also exist as an aldehyde (retinal), or as an acid (retinoic acid).
Based on the results of a six-year study of 600 patients with typical retinitis pigmentosa (RP), researchers concluded that, on average, the course of retinal degeneration was slower among patients receiving a daily vitamin A palmitate supplement (15,000 IU) than was the disease course among those not taking this dosage. There was about a 20 percent slower rate of decline of remaining retinal function (8.3 percent) per year in the 15,000 IU dose group versus the control (trace dose) group (10.0 percent), as monitored by electroretinographic (ERG) amplitudes. The results also suggested that the course of disease might be faster on averageamong patients receiving a daily high dose supplement of vitamin E (400 IU) than among those receiving a trace dose of vitamin E. It is recommended that most adult patients with the common forms of RP take a daily 15,000 IU supplement of vitamin A palmitate under the supervision of a doctor and avoid the use of high dose supplements of vitamin E, such as 400 IU.
It should be cautioned that regular long-term intake in excess of 25,000 IU vitamin A palmitate has been associated with liver toxicity. Side effects and complications from very high doses include liver toxicity, persistent headache, joint or bone pain, appetite loss, weight loss, nausea, vomiting, unusually dry skin, increased hair loss, and fatigue. When taken during pregnancy, high-dose vitamin A has also been associated with birth defects. In addition, since mutations in certain genes may cause the build-up of a toxin called A2E (a break-down product of vitamin A), vitamin A supplementation nutritional therapy is not recommended for some individuals with Stargardt disease. It is therefore recommended that individuals be given a yearly liver function test and that supplementation should be avoided by individuals who are pregnant or who have certain forms of Stargardt disease.
If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.