excess vitamin d

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Vitamin D

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Vitamin D
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Method of Action

Consequences of Deficiency

Deficiency Symptoms

Recommended Dietary Allowances

Properties and Uses

Toxicity Levels

Food Sources

Description

Vitamin D is a steroid hormone that exists in two molecular forms:
vitamin D-3 (cholecalciferol) found in animal skin, and vitamin D-2
(ergocalciferol) found in yeast. These two forms are created by the
action of the sun's ultraviolet rays on the biological precursors
7-dehydrocholesterol and ergosterol. Vitamin D is essential for
calcium and phosphorus metabolism, and it is required for the normal
development of bones and teeth.

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Method of Action

Vitamin D can be acquired either by ingestion of preformed vitamin D
or by the conversion of 7-dehydrocholesterol, after exposure to
ultraviolet light. Ingested vitamin D is absorbed with the aid of
bile. Vitamin D is then transported to the liver where it is converted
into 25-hydroxycholecalciferol. This compound is transformed in the
kidney into the physiologically active form
1,25-dihydroxycholecalciferol (1,25-DHCC). 1,25-DHCC is then
transported to the intestinal mucosal cells, bone, and skeletal muscle
where it is stored, regulating calcium absorption and mobilization.
Vitamin D aids the absorption of calcium from the intestinal tract by
stimulating the synthesis of calcium-binding protein in the intestinal
mucous membrane. It also aids the resorption of phosphate in the renal
tube. Vitamin D mobilizes phosphate from the bone to maintain serum
phosphate levels, and stimulates the active phosphate transport.

Vitamin A, choline, vitamin C, unsaturated fatty acids, and phosphorus
assist absorption of vitamin D. Mineral oil or insufficient sunlight
can prevent vitamin D absorption.

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Properties and Uses

Vitamin D's clinical application is in the treatment of rickets and
osteomalacia. Rickets can be prevented in newborns by administering
vitamin D in proper amounts early in, and throughout the growth
period. If rickets do occur, large doses of the vitamin are given.
Osteomalacia is prevented by adequate vitamin D, calcium, and
phosphorus in the diet. Vitamin D must come from food, adequate
sunlight, or concentrated supplements. The pain and weakness
associated with vitamin D deficiency will usually disappear after one
to two months of treatment.

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Consequences of Deficiency

Vitamin D deficiency creates a deficient deposition of hydroxyapatite
in the bones. This is due to inadequate absorption of calcium from the
intestinal tract, and from the retention of phosphorus in the kidney.
This inadequate mineralization of the bones causes rickets in infants
and children, and osteomalacia in adults. Rickets can cause delayed
closure of the fontanelles, softening of the skull, soft fragile
bones, enlargement of the wrist, knee, and ankle joints, poorly
developed muscles, restlessness and nervous irritability. Delayed
tooth development can be a sign of rickets. Some children develop
rickets with vitamin D supplementation. This may be due to a genetic
error in vitamin D metabolism, usually renal tubular dysfunction.

Insufficient sunlight can create vitamin D deficiency by preventing
the conversion of 7-dehydrocholesterol to cholecalciferol. This type
of deficiency is most common in countries with limited sunlight, or
where the population dresses in a manner that reduces the sunlight
exposure.

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Toxicity Levels

Vitamin D taken in excess can cause pathological changes in the body.
Signs of vitamin D toxicity include excessive calcification of bone,
kidney stones, calcification of soft tissue, headaches, weakness,
nausea, vomiting, constipation, polyuria, and polydipsia.

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Recommended Dietary Allowances

RDA for adult males: 200 IU

RDA for adult females: 200 IU

RDA for children 7 to 10 years: 200 IU

RDA for infants: 200 IU

RDA for pregnant and lactating women: 200 IU

Difficulties in establishing requirements for vitamin D arise from the
limited number of food sources available, lack of knowledge of precise
body needs, and degree of synthesis in the skin by irradiation. The
amount needed can vary between winter and summer in northern climates.
In addition, life-style determines the degree of exposure to sunlight
and would therefore influence individual need. This is especially true
of the elderly and invalids who do not go outside and therefore may
need supplementary vitamin D. Growth demands in childhood, during
pregnancy, and during lactation necessitate increased intake.

The daily recommendation for young adults is 7.5 mcg and older adults
5.0 mcg. The RDA standard is 10 mcg, or 400 international units (IU),
of cholecalciferol daily for children and for women during pregnancy
and lactation. One IU of vitamin D is equivalent to biologic activity
of 0.025 mcg of pure crystalline vitamin D-3 (cholecalciferol).

Adults over 22 years of age need only a small amount of vitamin D.
Under normal circumstances their need is met by the vitamin D
contained in an ordinary mixed diet and by exposure to sunlight.
Adults who work at night and those whose clothing or living customs
shield them from sunlight need somewhat more vitamin D in their diet.

No extra benefit is obtained from taking more than 400 IU daily except
for therapeutic reasons; then, dosages can range from 1,500 to 2,800
IU daily.

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Food Sources

· Fish Liver Oils · Egg Yolk · Herring · Kippers · Lard

· Mackerel · Salmon · Sardines · Shrimp · Tuna

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Summary Deficiency Symptoms

· Rickets In Children
· Soft Fragile Bones
· Enlarged Joints
· Bowed Legs
· Deformation of Bones In:
· Chest

Spinal Cord
· Pelvis
· Tetanic Convulsions In Infants
· Osteomalacia In Adults
· Inability of the Body to Metabolize Calcium

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