Vitamin D (Vitamin D2 and D3)

What sample is needed for the estimation of 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.

What are the Indications for Vitamin D?

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

What is the history of Vitamin D?

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

How will you define Vitamin D?

1. These are a group of fat-soluble vitamins that affect calcium and phosphorus metabolism.
2. There is the effect of UV radiation on this vitamin.
3. Cholecalciferol (D3) in the liver is hydroxylated to 25-hydroxycholecalciferol.
4. In the kidneys, they are hydroxylated to dihydroxy metabolites.
5. PTH increases the production of 1,25,(OH)2 D3 in renal proximal tubules and causes increased intestinal calcium absorption.

How will you discuss the 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-hydrocholesterol in the skin is produced by sunlight (ultraviolet rays) and 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).

  What is the mechanism of absorption of  Vitamin D3?

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. Bile salts are needed for its absorption.
   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.

What are the Vitam D sources?

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 sources are milk, breakfast cereals, and supplements.
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, endogenous photosynthesis in the skin provides 90% of vitamin D, which may amount to 1.5 to 10 mg/day.

What are the Vitamin D3 sources?

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. Exposure to the sun for 10 to 15 minutes a week forms an adequate amount of vitamin D3.
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-dihydroxyvitamin D in the liver and kidneys.
    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 reaches various target organs.

11. Vitamin D receptors (VDR) are present in the nucleus.
12. The binding of vitamin D3 to VDR of target cells now acts as a transcription factor.
13. This will ultimately lead to the absorption of Calcium in the intestine.
14. Activation of VDR in the intestine, bone, kidney, and parathyroid glands maintains calcium and phosphorus in the blood.

What are the 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 increases 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 normal Ca⁺⁺  in bone and plasma.

What is the outcome of a deficiency of vitamin D?

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

What is the 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. An increased vitamin D level increases intestinal absorption and causes excessive bone resorption.
4. Increased vitamin D leads to increased calcium and suppresses the PTH.

What are the causes of Vitamin D deficiency?

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 (Bone-softening diseases like):
   1. Rickets in children.
   2. Osteomalacia in adults.
   3. Osteoporosis.
   4. Recent evidence is that deficiency may be associated with cancers of the colon, breast, and pancreas.
   5. This may be associated with increased blood pressure and cardiovascular disease risk.

What group of people are at risk of Vitamin D deficiency?

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

How will you measure Vitamin D?

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

What is the 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
5. The recommended dose of vitamin D for adults is 5 µg/day.

What are the causes of increased levels of Vitamin D?

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

What are the causes of decreased levels 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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