Many Rp patients have been unwisely warned away from vitamin E based on a report that the benefits of vitamin A therapy are diminished when vitamin E is consumed at the same time. This is true, but there are many other metabolic functions for which vitamin E is essential. It is a very narrow view to advise RP patients away from vitamin E. There is more to the retina than just vitamin A.
Another area of the retina, the retinal pigment epithelium (RPE), which is dysfunctional in RP patients, requires selenium and vitamin E for proper function. The RPE consists of only 400,000 phagocyte cells lined up in a single-cell layer that ingest foreign particles and serve as a barrier between the photoreceptors and the blood supply (choroid). The rod (night vision) cells renew themselves by shedding about 10 percent of their used up vitamin A, a process that begins with light stimulus upon awakening in the morning. Normally the used up vitamin A passes through the RPE layer into the blood stream for disposal. If the used-up vitamin A and other cellular debris is trapped and oxidized (hardened) within the RPE layer, the RPE becomes clogged and nutrients and oxygen can no longer pass through to the hundreds of millions of photoreceptor cells serviced by a comparatively sparse number of RPE cells.
An antioxidant enzyme called glutathione peroxidase within the RPE layer is produced from selenium and vitamin E. The RPE layer becomes sick without glutathione peroxidase activity. The RPE layer also helps to convert and transport omega-3 fats, as found in cold water fish, into DHA, which comprises the myelin sheath that lines the photoreceptors. All nerve cells in the body crave DHA for proper function and a lack of DHA is a hallmark of RP and many other nerve disorders (schizophrenia, depression, multiple sclerosis, Alzheimer's etc.).
The liver normally stores a back-up supply of vitamin A unless it is malfunctioning. So the daily consumption of vitamin A is not as critical as is vitamin E and selenium. Typical daily consumption of vitamin E from the diet is only around 10 units; selenium around 50 micrograms. Adults reduce cardiovascular disease risks by consuming 100 or more units of natural-source vitamin E (labeled as d-alpha tocopherol). Rp patients should be reminded that RP could be considered a vascular disease because of the poor retinal blood circulation typical of this disease. Numerous studies point to the important role of vitamin E in maintaining retinal health. To solely consume vitamin A supplements is to deprive other parts of the retina of a necessary antioxidant nutrient-vitamin E. Photoreceptors also die without vitamin E.
It has long been known that vitamin A and E compete for absorption in the digestive tract when consumed at the same time. Both of these vitamins are fat-soluble and plentiful amounts of digestive enzymes improve absorption, which may be a problem among many RP patients. This reporter strongly recommends digestive enzymes for RP patients. This reporter's best advice is to consume vitamin E at a different meal other than vitamin A, to give the liver a chance to metabolize both of these nutrients separately. For those RP patients who are still wary of taking vitamin E, at least consume 200 micrograms of selenium daily. RP patients need need to recognize vitamin A has NOT been proven to save nor improve their sight, it has only been shown to slow down the progress of the disease by 7 years if a nutritional regimen is begun early in life. The water soluable form of vitamin A is recommended because it is easier to absorb, further evidence that digestive enzymes should be consumed along with these nutrients in a meal (not on an empty stomach).
Vitamin A palmitate is the preferred form of vitamin A because it is possible that RP patients may have problems converting beta carotene into vitamin A.
The drawbacks of the palmitate form of vitamin A is that it...
A) can build up to toxic levels in storage in the liver, but this is very
unlikely. Only 20 cases of vitamin A overdose are reported in the US annually and most cases are among those individuals with liver disease.
B) Beta carotene is a safer form of vitamin A in the sense that excess amounts are stored in the skin, preventing excess storage in the liver. However....
C) Alcohol should not be consumed as it interferes with vitamin A and zinc metabolism in the liver.
D) Both vitamin A palmitate, beta carotene, lutein and vitamin E are "fatty" vitamins (fat soluble) and thus compete for absorption in the digestive tract, storage in the liver and transport from the liver to the retina on cholesterol particles. Hence, the finding that vitamin E reduces the amount of vitamin A delivered to the retina. Best advice, take food supplements containing these nutrients at different times to avoid these problems.
E) The idea that vitamin E is toxic or somehow harmful is not backed by any science. The retina depends upon vitamin E as an antioxidant, particularly to protect other fats, such as the DHA from omega-3 fatty acids that line the rods and cone cells.
F) Yes, all of the current medical literature confirms that antioxidants work synergistically, that is, together they add up to more antioxidant protection.
Once an antioxidant like vitamin C becomes oxidized (often by sunlight in the eye) then vitamin A comes along and donates an electron to it and
reinvigorates its antioxidant action. Kind of like being brought back to
life. Vitamin C donates electrons to vitamin E and vitamin E donates