Vitamin D can be manufactured in the skin on exposure to
sunlight, or obtained from the diet. It's important as a
protector against cancer, in ensuring a robust immune
system, as a regulator of blood pressure and in enabling
the proper secretion of insulin. But it is in its
interaction with the essential mineral, calcium, and
consequently vital role in the development and maintenance
of strong, healthy bones, that vitamin D is best known.
Adequate blood calcium levels are essential for the proper
functioning of the nervous system and a sufficient supply
of vitamin D is vital for the maintenance of these levels.
If blood calcium falls too low because of a deficiency of
the vitamin, the body will respond by withdrawing calcium
from the most immediately available alternative source,
which is the large quantities stored in the bones.
In extreme cases, thankfully now rare, though by no means
unheard of even in the developed world, the consequence of
this process is the deficiency disease known as rickets, in
which bones are stripped of minerals, become soft or
brittle and in the load bearing limbs may be bowed. Since
the demand for calcium is at its greatest in rapidly
growing bones, the disease is tragically most common in
infants and children.
Even fully formed adult bones, however, require a constant
supply of calcium for continuing repair and regeneration,
and deficiency may result in a progressive loss of bone
density, or osteoporosis, which is a factor in many of the
fractures commonly suffered by the older population.
Vitamin D deficiency has also been identified as a cause of
general muscular pain and weakness in both children and
adults, with consequently increased incidence of the falls
which so often lead to these fractures in already weakened
bones in the elderly.
Traditionally it has been assumed that sufficient vitamin D
for the avoidance of deficiency can be synthesised through
the exposure of the skin to sunlight. But the problem is
that a large proportion of the population in the affluent
world lives in latitudes 40 or more degrees above or below
the equator where there is very limited sunlight for six
months of the year. They work indoors in towns and cities
whose buildings in any case screen out a large proportion
of the available sunlight before it reaches ground level.
And when they do manage to get outdoors in the summer
months, they are increasingly inclined to smother
themselves in high factor sunblock.
In these circumstances the traditional view appears
questionable at best, if not downright complacent. And the
situation is even worse for the elderly, who may not only
enjoy even less exposure to the sun than the young, but are
less able to make use of that which they do obtain.
Unfortunately there are few good natural food sources of
vitamin D, and the best source, oily fish such as sardines,
mackerel and salmon is one which many people, and perhaps
children in particular, often find unpalatable. The
situation has improved somewhat with the fortification of
milk, orange juice, bread and some cereal products, but it
may still be difficult for individuals to ensure they
obtain a sufficient intake of the vitamin, particularly
because the amounts added to different foods and drinks are
very variable.
No Recommended Dietary Allowance (RDA) has been established
for vitamin D because the requirement will vary enormously
depending on the amount of exposure to sunlight enjoyed by
the individual. But the Food and Nutrition Board has
suggested 200 IU (5mcg) for infants, children, and adults
up to 50, rising to 400 IU for the 50-70s, and 600 IU for
the over 70s, as an "Adequate Intake" of the vitamin from
food on the assumption that none is being obtained from
sunlight.
These figures, however, are generally regarded as
conservative, and even for those individuals fortunate
enough to enjoy regular exposure to good quality sunlight,
a strong body of orthodox opinion recommends the intake of
400 IU (10 mcg) of vitamin D as part of a multi-vitamin and
multi-mineral supplement. Higher doses still, however, are
recommended for the over 65s, those with less than optimal
liver or digestive health, those living in less
advantageous climates and those who spend the majority of
their time in indoor occupations. The recommended
supplementary dose is a further 400 IU, for a total of 800
IU.
But some specialised nutritional practitioners and
therapists, of course, are inclined to recommend even
higher doses for optimum health. Although vitamin D is fat
soluble and therefore has the potential to accumulate in
the liver, this appears extremely unlikely to cause
problems in practice. The upper safe limit suggested by
the Food and Nutriton Board is 2,000 IU (50 mcg) but recent
research suggests that this is a very cautious figure and
that intakes of up to 10,000 units a day should present no
risk to generally healthy individuals.
For maximum effect, however, vitamin D supplementation
should be always be combined with adequate dietary calcium
- supplemented if necessary to achieve an intake of 1,000 –
1,200 mg per day of this essential mineral.
----------------------------------------------------
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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