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.
Recommendation
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).
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