Vitamin A is one of nature's most valuable anti-oxidants,
and is also vital for preventing and fighting infection.
Well known animal sources are foods such as egg yolks, milk
and liver, along with the traditionally reviled fish liver
oils.
Plant sources, however, will be more palatable for many,
and may also have the advantage of providing additional
anti-oxidant activity.
"Carotenoids" is the generic term used to describe a large
range of more than 600 pigments synthesized by plants. In
modern Western diets those most frequently encountered are
alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein,
zeaxanthin, and lycopene.
Much attention has been focussed on alpha-carotene and
beta-carotene as these can be synthesised by the body to
form vitamin A, whereas this is not true of lutein,
zeaxanthin, and lycopene.
Alpha and beta-carotene from plant foods are readily
synthesised into vitamin A by the body. But only about 20%
of dietary alpha-carotene will be used in this way, the
remainder will function as a highly effective anti-oxidant
in its own right, particularly within the fatty membranes
of the body's cells. The same is true of the better known
beta-carotene, except that this is much more active in
terms of vitamin A provision, around 40% of dietary intake
being converted into vitamin A. Surplus beta-carotene
functions as an anti-oxidant in its own right, and also
provides a significant boost for the immune system.
Both alpha and beta-carotene are highly fat-soluble
anti-oxidants and therefore particularly effective in
protecting against free radical damage to the vital fatty
structures of the body's cells, such as the membranes.
Research also suggests that high levels of carotenoids in
the blood may help prevent the oxidation of Low Density
Lipids (LDLs), the so-called "bad cholesterol", which is
now heavily implicated in the development of the
atherosclerosis, or hardening of the arteries which is a
common precursor of cardio-vascular disease such as heart
attack and stroke. One study of 5,000 middle aged and
elderly adults showed a reduced heart attack risk of
between 45-55% for people following a high beta-carotene
diet, the higher figure being in respect of smokers within
the group.
Numerous studies, too, have demonstrated the potential of
beta-carotene as a weapon against cancer. This is probably
because of its general anti-oxidant function, but also
because of its proven role in keeping open the pathways
between cells, which are vital to allow the immune system
to kill off cancer cells in the early stages of the disease.
Conventional medical wisdom tends to accept the value of a
diet rich in carotenoids but, confusingly, argues that the
positive effects may be due to factors associated with such
diets other than the carotenoids themselves. But
alternative practitioners, of course, admit to no such
doubts and are convinced of the benefits – particularly of
the highly vitamin A active beta-carotene.
Whilst affirming the benefits of a diet naturally rich in
carotenoids - ie in the kinds of fruits and vegetables
detailed below, they insist that the maximum benefits of
alpha and beta-carotene, the latter particularly, can only
be secured through high dosage supplementation.
Practitioners argue that studies discounting the effects of
such supplementation are flawed because they have looked
only at dosages too low to be effective.
And certainly the dosages they recommend appear massive –
between 70,000 and 90,000 IU being proposed as the optimum
to assist in the fight against both heart disease and
cancer. To get this in perspective, these figures are
equivalent to around 42,000 and 54,000 mcg of beta-carotene
respectively, that's to say approximately 3 to 4 cups of
cooked carrots (around 13,000 mcg each).
Now, clearly an awful lot of fruit and vegetables need to
be consumed to achieve the kind of intake of beta-carotene
that the alternative practitioners recommend. And it also
needs to be noted that optimum absorption of carotenes
depends on the presence of a reasonable amount of dietary
fat. So chopping, pureeing, and cooking carotenoid rich
vegetables in oil is the ideal way to maximise the
bio-availability of these nutrients. But it's neither
convenient nor appetising. And whilst an 8 fl oz glass of
carrot juice provides around 22,000 mcg (37,000 IU) of
beta-carotene, would you consider giving up your morning
coffee in its favour? Me neither!
But apart from the convenience, another point in favour of
supplementation is that it appears not to be harmful in any
likely dosage. In fact the only side effect to have been
noted even from doses as high as 250,000 IU has been a
benign, if unflattering, "fake tan" skin pigmentation,
which very quickly vanishes upon the reduction of the dose.
So it appears that supplementation may do some good, is
extremely unlikely to do any harm, but for best results
should be taken as part of a normal daily diet already well
supplied with carotenoid rich foods.
----------------------------------------------------
Steve Smith is a freelance copywriter specialising in
direct marketing and with a particular interest in health
products. Find out more at
http://www.sisyphuspublicationsonline.com/LiquidNutrition/In
formation.htm
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