Friday, August 16, 2013
Vitamin A and Transverse Myelitis
As with most vitamins, keeping Vitamin A (retinol) levels within a normal range is important; too little or too much may cause problems.
Vitamin A occurs in dairy products like milk. It also occurs in eggs, fish, and animal liver (probably the richest dietary source of vitamin A). It does not occur in nature by itself, but many dark-green or dark-yellow plants (eg the carrot) contain 'carotenoids' (eg beta-carotene) that can be converted to vitamin A within the gut, and in turn converted in the body to ‘retinal’ and ‘retinoic acid’. Retinal is known to contribute to 'rhodopsin' (visual purple), the light sensitive pigment within both rod and cone cells of the retina. When in abundance, Vitamin A is stored in the human liver.
A diet rich in fruits, whole grains, nuts and vegetables (ie high in carotenoids) has been said to protect against lung cancer and maybe prostate cancer, but there is no evidence to date that supplements do protect against cancer; in fact two large-scale long-term studies have shown regular supplements (over and above good diet) were associated with increased cancer rates. There has been speculation that vitamin supplements (A, C, E, and copper and zinc) might improve the outcome for those at danger for, or with early, macular degeneration, but long term studies (eg the AREDS studies) have shown that Vitamin A (in the form of beta-carotene) is not required for the improvements, even though we know it contributes to night vision through rhodopsin.
Severe lack of vitamin A, which occurs in countries with starving populations, may lead to reduced ability to see clearly (often known as night blindness), and a dry or cloudy cornea. In addition, it can lead to changes in the skin (which becomes dry and scaly, with mucus secretion suppressed); reduced immune function against disease; reduced normal maintenance of heart, lung and kidney cells; reduced functioning of bone-remaking cells (osteoblasts/osteoclasts); reduced sperm production in men, and messed up hormone cycles in females; decreased synthesis of thyroid hormones, and elevated CSF pressure due to poor meningeal re-absorption of cerebrospinal fluid. There are some illnesses in the developing world that are known to lead to lowered Vitamin A - chronic chest infections, diarrhoea, measles, chickenpox and AIDS. In all of these we would seriously consider Vitamin A supplements very important.
However, excess Vitamin A and other retinoids can be toxic. This has been reported in Antarctic explorers (who had to survive by killing and eating the liver of their Huskie dogs) and Arctic explorers (who ate polar bear liver to survive). They were poisoned and died because the animals’ livers retained very high levels of the vitamin. Chronic intake of excess vitamin A has been reported to lead to increased intracranial pressure (pseudotumor cerebri), dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and death. Although hypervitaminosis A can be due to excessive dietary intakes (like our polar explorers), the condition is usually a result of consuming too much preformed vitamin A from supplements or therapeutic retinoids. It is worth noting that when people consume too much vitamin A, their tissue levels take a long time to fall after they stop, and liver damage from this is not always reversible.
So at this point, we may already be thinking we have to be careful and sensible about supplementing our diet for Transverse Myelitis, but I will come back to that later. First let us just look at when enough is enough...
The dietetics of Vitamin A
Because Vitamin A comes in different useful forms, we need some way of combining them all – particularly if you are taking supplements, and are not sure which form is in your supplement. So, Recommended Daily Allowances (RDAs) for vitamin A are given as mcg of Retinol Activity Equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids. (Don’t you hate all these acronyms!!). But there is more... Sorry this next bit is technical but crucial...
An RAE cannot be directly converted into an International Unit (IU) without knowing the source of vitamin A. So, an RDA of 900 mcg RAE for adolescent and adult men is equivalent to 3,000 IU if it is in a supplement as preformed vitamin A (retinol). However, this RDA is also equivalent to 6,000 IU of beta-carotene from supplements, 18,000 IU of beta-carotene from food, or 36,000 IU of alpha-carotene or beta-cryptoxanthin from food. Did you get all that?
Basically, a mixed diet containing 900 mcg RAE provides between 3,000 and 36,000 IU of vitamin A, depending on the foods consumed.
You should be aiming for a reasonable average amount of daily vitamin A, say about 5,000 IU for adults and children age 4 and older. Children in the first year of life probably need slightly more than half of this. Women may need slightly less overall, unless they are lactating in which case requirements may nearly double.
Just as a guide:
3 Oz of beef liver (pan fried) will give you 6,500 IU
1 whole sweet potato baked in its skin will give you about 1,400 IU
Half a cup of frozen Spinach boiled will give you about 550 IU
Half a cup of raw carrots will give you 450 IU
1 piece of pumpkin pie will give you nearly 500 IU
1 cup of soft serve ice cream will give you about 250 IU
1 cup of ricotta cheese will give you about 500 IU
Multivitamin supplements typically contain 2,500–10,000 IU vitamin A, often in the form of both retinol and beta-carotene. Up to 35% of the general population may be using supplements containing vitamin A in the belief they help vision, skin, and general recovery from illness.
In my last blog on Transverse Myelitis and Vitamins, I took the example of Multiple Sclerosis as possibly informative to us, given they are both serious problems with the myelin sheath. The following summary is taken from the ‘Overcoming Multiple Sclerosis’ site (http://www.overcomingmultiplesclerosis.org/Recovery-Program/Supplements/Other-Supplements/). I think we should take this seriously.
“The evidence is now clear, taking multivitamins, particularly the antioxidants vitamin E and A and beta-carotene, cannot be considered beneficial, or even safe, and should be avoided by people eating a healthy diet.”
“The very influential Nurses’ Health Study in the US, looking at the development of MS in over 176,000 US nurses, found no association between the intake of the antioxidant vitamins C or E, or dietary carotenoids (such as beta carotene) and the development of MS, either taken as vitamin supplements, or calculated from the foods they ate. Recent evidence has raised serious concerns about taking multivitamins regularly on the basis that they increase overall death rates in controlled clinical trials. They are not recommended in MS, although individual vitamins may be necessary for people following a vegan plus fish diet, including vitamin B12 and iron. B group vitamins in general are thought to be helpful for optimal brain function.’
The Bottom Line
If you have Transverse Myelitis, at this stage of our knowledge, there is no reason to be taking more Vitamin A than the average recommended Daily Allowance (RDA). As far as your disease process will allow (and we are all different), you will recover best if you eat a normal diet rich in Green and Yellow vegetables, Grains, Nuts, Fish and supplemented by a reasonable amount of milk products (milk, cheese, yoghurt and ice cream) and occasionally supplemented with good old (or heavily disguised) liver and bacon about once a fortnight.
Keep getting the physiotherapy, lots of natural sunshine and supplement your vitamin D in accordance with what your doctor or dietitian tells you.
PS. I do apologise for all the technical and/or unpronouncable words. I did try to keep them to a minimum (believe it or not).