Vitamin D (Vitamin D2 and D3)

Sample

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)

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

Pathophysiology

1. Vitamin D is a fat-soluble vitamin and it is hormone-like steroids.
2. 7-hydrocholesterol 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).
   2. Vitamin D3 (Cholecalciferol).

4.   Vit.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.

5. Sources of VitamD2 are:
   4. A dietary source of fish that is rich in Vit.D.
   5. The artificial source is milk, breakfast cereals, and supplement.
6. Vit.D3 sources are:
   1. Animal food.
   2. Fatty fish.
   3. Eggs.
   4. Liver.
   5. Butter.
   6. Vitamin D3 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 the 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. The people with more melanin needs more time.
7. 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 released into circulation.
   2. It binds to a carrier protein (vitamin-D binding protein VDBP) and goes to various target organs.

4. 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.

8. Functions of vitamin D:
   1. Vit.D major role is to regulate serum calcium and phosphorus in the blood by:
      1. Promoting their absorption from food in the intestine.
      2. By promoting the reabsorption of calcium in the kidneys.
         1. This will prevent Rickets from growing children.
         2. Prevents osteomalacia in adults.
         3. Prevents hypocalcemic tetany.
         4. Vitamin D corrects and maintains the concentration of ionized calcium.
9. Vit.D inhibits parathyroid hormone secretion from the parathyroid gland.
10. Vit.D promotes:
    1. The immune system by increasing phagocytosis.
    2. Anti-tumor activity.
    3. Immunomodulatory function.
11. Role in calcium absorption:
    1. It stimulates intestinal absorption of calcium and phosphorus.
    2. It stimulates the PTH dependant 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.
12. 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.
13. 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 suppress the PTH.

Causes of Vit.D deficiency are:

1. Inadequate dietary intake.
2. Inadequate sunlight exposure.
3. Malabsorption syndrome.
4. Liver or kidneys disorders.
5. Metabolic hereditary disorders.

1. Vit.D deficiency leads to:
   1. Bone softening diseases like,
      1. Rickets in children.
      2. Osteomalacia in adults.
      3. Osteoporosis.
   2. Recent evidence is that deficiency may be associated with cancers of the colon, breast, and pancreas.
   3. This may be associated with an increase in blood pressure and cardiovascular disease risk.

People at risk of Vit.D deficiency are:

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

Measurement of Vit.D:

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

Normal Total Vit.D:

Source 1

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

Other sources

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

Increased level of Vit.D:

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

Decreased level of Vit.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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