V

vitamins and health Vitamins are organic
micronutrients essential for health and the body’s
proper growth, development, and function. They
interact with each other or with other biochemi-
cals in the body, functioning as cofactors or coen-
zymes to carry out activities of energy conversion
(METABOLISM) though do not themselves provide
energy to the body. With the exception of vitamin
D, dietary sources provide the vitamins the body
requires.
There are 12 vitamins that are essential for
health. The 8 B vitamins and vitamin C are water
soluble; the body cannot stockpile stores of them
(except in limited accumulations within the BLOOD
circulation and the LIVER) and thus requires regu-
lar consumption to maintain levels adequate to
support health. Most healthy people can obtain
the vitamins their bodies need for normal func-
tioning through dietary sources. Vitamins A, E, D,
and K are fat soluble; the body stores excess
amounts of these vitamins in adipose (fatty) tissue
and draws from these supplies when dietary
intake does not meet needs.
Vitamin deficiency may develop when dietary
consumption is inadequate, as a result of gastroin-
testinal disorders that interfere with nutrient
absorption or owing to interactions with medica-
tions. Chronic health conditions may drain the
body of important NUTRIENTS, including vitamins.
Untreated vitamin deficiency can cause potentially
serious health conditions such as SCURVY,RICKETS,
and NIGHT BLINDNESS.
Vitamin toxicity occurs most commonly as a
consequence of excessive vitamin supplementa-
tion and can have serious or permanent conse-
quences. Metabolic disorders and medications that
interfere with vitamin metabolism are also com-
mon culprits. Vitamin toxicity is more common

with the fat-soluble vitamins because they accu-

mulate in the body. Vitamin toxicity also is possi-

ble with extreme overconsumption of

water-soluble vitamins, usually the result of

higher levels in the blood circulation than the

body can excrete.

Vitamin toxicity is more likely to occur

when taking a multiple vitamin supple-

ment and individual supplements that

supply significantly greater than the

needed amounts of certain vitamins.

Vitamins A; E; and the B vitamins

niacin (B 3 ), pantothenic acid (B 5 ), pyri-

doxine (B 6 ), and folic acid (B 9 ) present

the greatest risk for toxicity.

Vitamin A (Retinol)

Vitamin A is essential for proper functioning of the

photoreceptor cells (rods and cones) of the RETINA,

maintains the health of the SKIN, and appears to

have some antiviral capabilities. It is also crucial

for growth and development in children. The liver

stores vitamin A, a fat-soluble vitamin, and

releases it into the blood circulation as the body

needs it. The primary dietary sources for vitamin

A are foods that supply beta-carotene, which the

body converts to retinol. Such foods include yel-

low vegetables and fruits, green leafy vegetables,

egg yolks, and fish liver oil.

Vitamin A deficiency results in disturbances of

vision, including impaired dark adaptation (slow-

ing of the ability of the eyes to adjust to changes

in lighting) and night blindness. In children, vita-

min A deficiency can stunt growth and impair

cognitive development. These developmental dis-

ruptions can have permanent consequences,

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