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Vitamins A, D, E and K
Micronutrients for bones, muscles and nerves
The fat-soluble vitamins – A, D, E and K
– are needed in small amounts (as are all vitamins) for a variety of functions,
one of which is contributing to the growth and strength of your
bones. In
contrast to the water-soluble B complex and
C vitamins, which are used or
excreted soon after ingestion and can be stored only in minute quantities,
fat-soluble vitamins can be stored in the body wherever
fat is deposited.
However, because these vitamins are essential to so many physiological
processes, they should be included in your
diet frequently.
 Researchers have identified several important functions of vitamin A, including
assisting in the growth of bone tissue and of strong tooth enamel, one of the
best natural shields against tooth decay. This vitamin also aids in the division
and growth of body cells, helps maintain normal
vision in dim light and protects
the skin and the lining of the nose and throat from infection. In addition, some
research indicates that people whose diets include plenty of vegetables that
supply vitamin A have a lower incidence of certain forms of cancer, including
skin cancer, than people who consume less of these foods.
The vegetables that provide you with vitamin A do so through chemicals called
carotenoids – vitamin A precursors that your body converts to vitamin A. The
most abundant carotenoid is beta carotene, found in such vegetables and fruits
as spinach, broccoli, sweet potatoes, carrots, pumpkin, tomatoes, apricots and
peaches. Vitamin A itself is found in generous amounts in egg yolks, dairy
products, oily fish and liver – and it occurs not as a precursor, but in a form
called retinol that your body uses directly. This does not mean, however, that
these animal-derived foods are the best sources of vitamin A.
Animal-derived vitamin A is used in vitamin supplements, but any one taking
supplements should be careful. Doses that exceed 10 times the daily recommended
amount can be toxic, potentially causing tenderness or pain in bones as well as
liver and brain damage. Beta carotene and other carotenoids, however, are not
known to be toxic when you consume more than you need.
The Recommended Daily Amount (RDA) of Vitamin A is 800 RE for women– amounts
that are supplied by one large carrot.
 Vitamin D can be obtained from your diet, but it is also formed in your skin
when you are exposed to sunlight. The regulation of
calcium and
phosphorus
metabolism is vitamin D’s most important role. It promotes the intestinal
absorption of calcium, regulates the movement of calcium and phosphorus in and
out of bones and teeth, and maintains the proper levels of these two minerals in
the blood. By promoting an adequate blood level of calcium, vitamin D also
ensures the proper functioning of the nerves and
muscles.
Vitamin D occurs naturally in only a few common foodstuffs such as oily fish,
liver, eggs and butter, however, some milks and many
breakfast cereals are
fortified with this vitamin. No one should take vitamin D supplements without
medical supervision, since doses that contain more than 10 times the daily
recommended amount are extremely toxic.
Vitamin D is measured in micrograms. The RDA for women is 2.5
micrograms, which can be supplied by 35 grams of sardines.
 In contrast to vitamins A and D, vitamin E’s functions are not well delineated,
although many health and cosmetic claims have been made for it. What is known is
that vitamin E acts as an antioxidant, a substance that keeps oxygen from
combining with and altering fats. When the fats that are contained in cell
membranes react with oxygen, they break down into chemicals called peroxides,
and, consequently, the cell membranes are destroyed.
Because of its antioxidant function, some researchers believe that vitamin E may
play an important role in inhibiting the long-term cellular deterioration that
occurs as part of the ageing process and that may be due to oxidation. As a
protector of cell membranes, vitamin E may also keep blood cells from breaking
down. Among the good sources of vitamin E are oats, leafy green vegetables,
whole-wheat products, nuts and virtually all vegetable oils except coconut oil.
Vitamins E, which exists in several slightly different chemical forms, is
measured in tocopherol equivalents (TE); tocopherol is another name for the
vitamin. One milligram of vitamin E equals one TE. An estimated safe intake is 8 to 10 TE, which is supplied by 15 grams of corn
oil.
 Although your body does not make vitamin K directly, bacteria in your intestines
can produce this vitamin, which reduces the amount you need from dietary
sources. Used by your liver to make blood clotting factors, vitamin K is found
in spinach, kale, cabbage, cauliflower and liver, among other foods.
No RDA has been determined for vitamin K either. The suggested intake is 70 to
140 micrograms per day, the amount contained in 50 grams of spinach.
Other conditions also need to be satisfied; these include adequate intake of
other nutrients needed for bone formation, such as Calcium, vitamins C and K,
zinc and
copper, and a high mechanical demand on the skeleton through an
adequate level of
weight-bearing
exercise.
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