Vit Min

• Vitamins


  Organic compounds that are dietary essentials, required in small amounts through the diet as they cannot be synthesized in the body
• Deficiency states


  • Primary - results from inadequate intake
  • Secondary - due to physiologic or pathologic processes
• Groups who must be given vitamins

  • Growing children, and teenagers
  • Pregnant and lactating mothers
  • Critically ill; chronic alcoholic
  • Malabsorption problems
  • People who follow strict diets (e.g. vegetarians)
• Recommended Dietary Allowance (RDA)


  Also called Recommended Energy and Nutrient Intake (RENI) or Recommended Dietary Intake (RDI)
• Estimated Average Requirement (EAR)

  Estimated requirement of a vitamin so that 50% of the population will be able to meet the necessary amount
• RENI/RDA


  Recommended intakes of micronutrients that is set at 2 standard deviations above the mean (EAR)
• At 2 SD above the average amount required, 97.5% of the population will be able to meet the recommended amount and will not develop deficiency or toxicity
• Fat-soluble vitamins


  Vitamins A, D, E, & K. Hydrophobic compounds absorbed with lipids, can be stored in the body, and only Vitamin K has a coenzyme function
• Water-soluble vitamins


  1. complex Vitamins, Ascorbic acid (Vit C). Function mainly as enzyme/cofactors/coenzymes, do not require fat/bile for absorption, generally have no precursor and are not stored
• 1. complex vitamins


  • Energy-releasing vitamins (B1, B2, B3, B7, B5)
  • Hematopoietic (B9, B12)
  • Other (B6)
• Vitamin A


  Retinol is the active form, beta-carotene is the most abundant precursor, can be obtained from animal and plant sources
• Oxidation of Vitamin A

  1. Carotenoids from vegetables can be oxidized to 2 molecules of Retinol

  2. Retinal (retinaldehyde) is formed from retinol

  3. Further oxidation of Retinal will give the acidic derivative, Retinoic Acid
• Functions of Vitamin A

  • Growth and maintenance of epithelial tissues
  • Vision: Mediator in the visual process as a constituent of rhodopsin (rods)
• Vitamin A deficiency can lead to keratinization of the skin and mucosal linings, xerophthalmia, and night blindness
• Vitamin A toxicity can cause bone pain, scaly dermatitis, enlargement of liver and spleen, nausea, and diarrhea
• Vitamin D


  Precursor is 7-dehydrocholesterol, active form is 1,25-dihydroxycholecalciferol/Calcitriol, sources include saltwater fish, liver, egg yolk, and fortified foods
• Vitamin D Synthesis


  1. 7-Dehydrocholesterol is converted to Vitamin D3 (cholecalciferol) upon exposure to UV light

  2. Cholecalciferol is converted to 25-hydroxycholecalciferol in the liver

  3. 25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalciferol (calcitriol) in the kidney
• Functions of Vitamin D

  • Increases calcium and phosphate levels by stimulating calcium absorption in the intestines, calcium reabsorption in the kidneys, and calcium mobilization from bone
• 1. Dehydrocholesterol


  Converted into Vitamin D3 or cholecalciferol when exposed to UV light
• Vitamin D3 (cholecalciferol)


  Form that is prescribed (tablets) and also found in diet (milk and food)
• Vitamin D2 (ergocalciferol)


  Form from plant sources such as mushrooms
• Vitamin D synthesis


  1. Cholecalciferol transported to liver (stored) or converted into 25-hydroxycholecalciferol / calcidiol through hydroxylation reaction by 25-hydroxylase

  2. Transported to proximal tubules of the kidney to be activated and undergo another hydroxylation reaction through the action of 1-alpha-hydroxylase

  3. Product: 1,25-dihydroxycholecalciferol / Calcitriol (active form of Vitamin D)
• Vitamin D


  • Increases calcium and phosphate levels
• Vitamin D functions in the intestines

  • Absorption of calcium through stimulation of the synthesis of calcium binding protein in the brush border of the intestinal mucosa
  • Stimulates phosphate absorption
• Vitamin D functions in the kidneys

  Increases renal tubular reabsorption of calcium
• Vitamin D functions in the bone

  Mobilizes calcium and phosphate through bone resorption
• Rickets


  Continued formation of osteoid matrix and cartilage which are improperly mineralized, resulting in soft pliable bones
• Osteomalacia


  Adult demineralization of preexisting bone, causing bone to become softer and more susceptible to fracture
• Calcidiol or inactive form of Vitamin D is reported when requesting a Vitamin D assay, while Calcitriol or active form is not measured
• Renal osteodystrophy


  Bone problem secondary to abnormality in the kidney (patients suffering with kidney diseases)
• Kidney function in Vitamin D production


  1. Kidney is important for the final step of producing an active Vitamin D

  2. In chronic renal failure, the renal failure results in an inability to produce 1,25(OH)2D (Calcitriol)

  3. Decrease in calcium absorption

  4. Low calcium triggers reactions to normalize the calcium level

  5. Bone calcium becomes the only important source of serum calcium
• Hyperphosphatemia and hypocalcemia in later stages of chronic kidney disease

  Stimulate parathyroid hormone secretion, and the resulting hyperparathyroidism further accelerates the rate of bone loss
• Treatment for renal osteodystrophy

  1. Vitamin D supplementation

  2. Phosphate binding drugs (for hyperphosphatemia, given to patients with CKD or renal disease)
• Decrease in Vitamin D due to abnormal kidney function

  Leads to low calcium, low phosphorus, and release of parathyroid hormone
• Effect of parathyroid hormone on the kidney

  Increases conversion of calcidiol from liver to calcitriol, increases calcium reabsorption and phosphorus excretion
• Effect of parathyroid hormone on the intestines

  No direct effect, but indirect effect through increased calcitriol which stimulates calcium and phosphate absorption
• Effect of parathyroid hormone on the bones

  Increases bone resorption to mobilize calcium and phosphorus
• In patients who are no longer urinating, there is elevated phosphorus, hence administrating phosphate-binding drugs
• Fibroblast growth factor 23 (FGF23)

  Hormone released by the osteoblasts, activated in times of chronic kidney disease, inhibits the activation of calcidiol to calcitriol and inactivates existing calcitriol, contributing to the weakening of the bone and increasing the rate of bone fractures in patients with kidney diseases
• Cases of dietary Vitamin D deficiency

  • Low-income group
  • Elderly (sedentary and minimal exposure to sunlight)
  • Strict Vegetarians (if diet is low in Ca, high in Fiber)
  • Chronic Alcoholics
  • Diseases causing Fat Malabsorption or severe liver and kidney disease
  • Chronic steroid use