Vitamin D

Sample for Vitamin D

1. Venous blood is needed to prepare the serum.
2. A random sample can be used.
3. The sample is stable at room temperature for 72 hours.
   1. The sample is stable at 22 to 25 °C.

Purpose of the test (Indications) for Vitamin D

1. Indicated in postmenopausal women to evaluate Vitamin D levels which are needed for the absorption of Calcium.
2. To evaluate the role of Vitamin D in osteoporosis.
3. To find the role of Vitamin D in the prevention of cancer.

History of Vitamin D

1. In 1822, it was found that rickets could be prevented by cod liver oil.
2. Rickets where there were muscles hypotonia and skeletal deformities.
3. After 100 years, it was found that the antirachitic factor in cod liver oil is vitamin D.
4. These antirachitic factors are collectively called vitamin D.
5. In 1925 led to the elimination of the widespread disease of nutritional rickets.
6. Vitamin D is now considered to be a hormone.

Pathophysiology of Vitamin D

1. Vitamin D is a fat-soluble vitamin, and it is a hormone-like steroid.
2. The naturally occurring fish liver oil is vitamin cholecalciferol (Vitamin D3).
   1. It is produced in the skin from ultraviolet activation of 7-dehydrocholesterol.
   2. 7-hydro-cholesterol in the skin by the sunlight (ultraviolet rays), converted into D2 and D3.
3. Vitamin D is found in two forms:
   1. Vitamin D2 (Ergocalciferol). It is a plant-derived vitamin.
   2. Vitamin D3 (Cholecalciferol).

  Vitamin D3 absorption:

1. In the diet, vitamin D is in two forms:
   1. Cholecalciferol (D3)
   2. Ergocalciferol (Vitamin D2).
2. 1. 25, (OH)2 D3 stimulates the intestinal absorption of Ca⁺⁺ and PO^//.
   1. For its absorption, bile salts are needed.
   2. It is stored in the liver and excreted in the bile.
3. Under the influence of the PTH, it helps for:
   1. Bone growth.
   2. Metabolism.

Vitam D sources are:

1. Diet is not the major source of vitamin D; the main source is skin exposure to sunlight.
2. Major dietary sources include irradiated foods and commercially prepared milk.
3. A dietary source of fish that is rich in Vitamin D.
4. The artificial source is milk, breakfast cereals, and supplement.
5. Small amount occurs in butter, egg yolk, liver,  salmon, sardines, and tuna.
6. Vitamin D2 is derived from plant sterols.
7. Vitamin D3 is provided by animals or of synthetic origin.
8. In normal adults, 90% of vitamin D is provided by endogenous photosynthesis in the skin, which may amount to 1.5 to 10 mg/day.

Vitamin D3 sources are:

1. Animal food.
2. Fatty fish.
3. Eggs.
4. Liver.
5. Butter.
6. Vitamin D3 is produced in the skin under the influence of sunlight.
   1. There is a special effect of ultraviolet light (ultraviolet B radiation).
   2. 7-dehydrocholesterol under the influence of ultraviolet-B light converted into vitamin D3.
   3. The wavelength of ultraviolet light is 270 to 300.
   4. These lights are present at sea level and not seen in the arctic circle.
7. An adequate amount of vitamin D3 forms when you are exposed to the sun for 10 to 15 minutes a week.
8. Don’t use sunblock.
9. Vitamin D formation depends upon the melanin contents. People with more melanin need more time.
10. Vitamin D from the skin or from food is converted into 1,25, dihydroxy vitamin D in the liver and kidney.
    1. 1,25, dihydroxy vitamin D is a hormonally active form of vitamin D and is released into circulation.
    2. It binds to a carrier protein (vitamin-D binding protein = VDBP) and goes to various target organs.

1. Vitamin D receptors (VDR) are present in the nucleus.
2. Binding of vitamin D3 to VDR of target cells, now VDR acts as a transcription factor.
3. This will ultimately lead to the absorption of Calcium in the intestine.
4. Activation of VDR in the intestine, bone, kidney, and parathyroid glands leads to the maintenance of calcium and phosphorus in the blood.

Functions of vitamin D:

1. Vitamin D’s major role is to regulate serum calcium and phosphorus in the blood by:
   1. Promoting their absorption of food in the intestine.
   2. By promoting the reabsorption of calcium in the kidneys.
   3. This will prevent Rickets from growing children.
   4. Prevents osteomalacia in adults.
   5. Prevents hypocalcemic tetany.
   6. Vitamin D corrects and maintains the concentration of ionized calcium.
   7. Vit.D inhibits parathyroid hormone secretion from the parathyroid gland.

2. Vitamin D promotes:
   1. The immune system by increasing phagocytosis.
   2. Anti-tumor activity.
   3. Immunomodulatory function.
3. Role in calcium absorption:
   1. It stimulates intestinal absorption of calcium and phosphorus.
   2. It stimulates the PTH-dependent reabsorption of calcium in the distal renal tubule.
   3. It helps PTH to mobilize the calcium from the bone.
   4. PTH, vitamin D, and calcitonin maintain a normal amount of Ca⁺⁺  in bone and plasma.

Deficiency of vitamin D leads to:

1. Rickets in the children in the growing age.
2. Osteomalacia in adults.
3. Prolonged deficiency causes osteopenia.
4. Hypocalcemia.

Toxicity of vitamin D:

1. Overdosage of vitamin D leads to metastatic calcification of soft tissues.
2. Hypervitaminosis of vitamin D (calcitriol) leads to hypercalcemia.
3. Increased level of vitamin D increases intestinal absorption and excessive bone resorption.
4. Increased vitamin D leads to increased calcium and suppresses the PTH.

Causes of Vitamin D deficiency are:

1. Inadequate dietary intake.
2. Inadequate sunlight exposure.
3. Malabsorption syndrome.
4. Liver or kidney disorders.
5. Metabolic hereditary disorders.
6. Vitamin D deficiency leads to:
   1. Bone softening diseases like:
   2. Rickets in children.
   3. Osteomalacia in adults.
   4. Osteoporosis.
   5. Recent evidence is that deficiency may be associated with cancers of the colon, breast, and pancreas.
   6. This may be associated with increased blood pressure and cardiovascular disease risk.

People at risk of Vitamin D deficiency are:

1. Infants on breastfeeding (human milk is deficient in Vit.D).
2. Occupation is when people are not exposed to the sun.
3. Individuals are too fatty with body mass index (BMI) >30 because Vitamin D is trapped in fatty tissues.
4. Malabsorption from GIT.
5. Patient with liver or kidney diseases.

Measurement of Vitamin D:

1. Measure 25-hydroxy D2 and D3 = Total Vit D.
2. Treatment is based on the total Vit.D level.

Normal Total Vitamin D:

Source 1

• 16 to 65 pg/mL
• Maternal concentration is 2-fold higher.

Another source

• 25-hydroxy vitamin D = 30 to 100 ng/mL

Other sources

1.  Indicate vitamin D deficiency = <20 ng/mL
2.  Insufficiency of vitamin D = 20 to 30 ng/mL
3.  Optimal level of vitamin D = >30 ng/mL
4. Toxic level of vitamin D = >200 ng/mL
   1. The recommended dose of vitamin D for adults is 5 µg/day.

Increased level of Vitamin D:

1. Excessive dietary supplement.
2. William syndrome. This is a rare genetic disorder.

Decreased level of Vitamin D:

1. Rickets.
2. Osteoporosis.
3. Liver diseases.
4. Renal diseases.
5. Inadequate dietary intake.
6. Inadequate exposure to sunlight.
7. Acute inflammatory diseases.
8. Familial hypophosphatemic rickets.

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