c. Vitamin A.
(1) Vitamin A is essential for growth, especially in bone, reproduction, and
embryonic development. It appears to be essential for the integrity of epithelial cells. It
functions in the rods of the retina to form rhodospin that is necessary for night vision.
(2) Natural sources of vitamin A are milk, butter, eggs, green vegetables,
liver, and kidney.
(3) Common deficiency states are night blindness, keratinization (scales),
and dryness of the epithelium, particularly in the extremities, cornea, and conjunctiva.
Toxicities seen in overdoses are relatively nonspecifics including irritability, vomiting, dry
skin, pruritis, and loss of appetite, headache, gingivitis, and mouth fissure. Diagnosis of
overdose is usually made following the appearance of tender, deep tissue swelling on
the extremities and in occipital region of the head. Acute intoxication in infants is seen
by an increase in intracranial pressure.
d. Vitamin D.
(1) Vitamin D facilitates the absorption of calcium from the small intestine,
which is essential in the mineralization of bone and maintaining normal plasma calcium
(2) A few natural sources of vitamin D are liver dairy products and fish.
In adults, vitamin D deficiency is most likely to occur in times of increased calcium
requirements (pregnancy and lactation). This results in "adult rickets" or osteomalacia,
which is a decrease in bone density. Gross bone deformities occur only in advanced
stages of the disease.
(3) In children, because of reduction in absorption of calcium and
phosphate, the bones do not mineralize properly. Therefore, the bones are not able to
support the body weight-giving rise to the deformities of rickets.
(4) Toxicity or overdose is usually the result of "mega vitamin" therapy.
Initial signs and symptoms are those associated with hypercalcemia (weakness, fatigue,
headache, nausea, vomiting, and diarrhea). Prolonged hypercalcemia may result in
deposition of calcium salts in the soft tissues, most significantly in the kidney.
e. Vitamin E.
(1) There is much controversy over vitamin E therapy, but it appears to be
essential for normal growth maintenance. A biological antioxidant protects unsaturated
fatty acids and membrane structures. Natural diet sources include vegetable oils and