vitamin D

Examples of vitamin D in the following topics:

• Metabolic Functions

  • Vitamin D refers to a group of fat-soluble steroids responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc.
  • Vitamin D deficiency is associated with impaired bone development in children, which leads to the development of rickets and a softening of bones in adults.
  • Deficiency in vitamin D has been termed a modern disorder associated with both a poorer diet and reduced time spent outside.
  • Vitamin D is produced in the two innermost strata of the epidermis, the stratum basale and stratum spinosum.
  • Vitamin D from the diet or that is synthesized by the body is biologically inactive; activation requires enzymatic conversion in the liver and kidney.

• Osteomalacia and Rickets

  • Women who avoid sun exposure have very low levels of vitamin D.
  • Women who wear a burqa can have undetectable levels of vitamin D despite living in a sunny region.
  • The predominant cause is a vitamin D deficiency.
  • Vitamin D is required for proper calcium absorption from the gut.
  • Treatment involves increasing dietary intake of calcium, phosphates, and vitamin D.

• Onset, Duration, and Half-Life of Hormone Activity

  • Vitamin D is a hormone that has a half-life of one to two months.
  • If one obtains vitamin D solely through sun (UVB) exposure during the summer months, serum vitamin D levels will be critically low by late winter.
  • This is one reason why current recommendations are to take vitamin D supplements in order to maintain serum vitamin D levels throughout the year.

• Bone and Calcium Homeostasis

  • Supplementation with vitamin D and calcium slightly improves bone mineral density.
  • Vitamin D is converted to calcidiol in the liver.
  • Part of the calcidiol is converted by the kidneys to calcitriol, the biologically active form of vitamin D.

• Calcium and Phosphate Balance Regulation

  • In the typical Australian diet, there is about 1200 mg/d of calcium.
  • In addition, absorption is regulated by active vitamin D and increased amounts of this increase Ca++ absorption.
  • Absorption is controlled by vitamin D while excretion is controlled by parathyroid hormones.
  • However, the distribution from bone to plasma is controlled by both the parathyroid hormones and vitamin D.
  • This increases ionized calcium levels by increasing bone re-absorption, decreasing renal excretion and acting on the kidney to increase the rate of formation of active Vitamin D, thereby increasing gut absorption of calcium.

• Rheumatism and Arthritis

  • The discovery of the vitamin D receptor (VDR) in the cells of the immune system and the fact that activated dendritic cells produce the vitamin D hormone suggested that vitamin D could have immunoregulatory properties. 25(OH)D3 plasma levels have been found inversely correlated, with the RA disease activity showing a circannual rhythm (more severe in winter).
  • Recently, greater intake of vitamin D was associated with a lower risk of RA.
  • A significant clinical improvement was strongly correlated with the immunomodulating potential in vitamin D-treated RA patients.

• Paget's Disease

  • Along with osteomalacia, rickets, and osteoporosis, Paget's disease is associated with vitamin D deprivation.
  • If one chooses to avoid exposing unprotected skin to the UVB radiation of the sun, then one must compensate for this lack by taking vitamin D supplements or risk the development of one of these diseases.
  • In general, patients with Paget's disease should receive 1000–1500 mg of calcium, adequate sunshine, and at least 400 units of vitamin D daily.

• Liver Function

  • The liver stores a multitude of substances, including glucose (in the form of glycogen), vitamin A (1–2 years' supply), vitamin D (1–4 months' supply), vitamin B12 (1–3 years' supply), iron, and copper.

• Anticoagulants

  • However, they are also the main dietary source of vitamin K, which is necessary for blood clotting to occur.
  • However, if you are taking warfarin to prevent heart attacks, then it is necessary to control intake of leafy green vegetables since warfarin is an antagonist to vitamin K and could work improperly if the diet is high in vitamin K.
  • Coumadins such as warfarin are oral anticoagulant pharmaceuticals that antagonize the effects of vitamin K1.
  • Depletion of vitamin K by coumadin therapy increases risk of arterial calcification and heart valve calcification, especially if too much vitamin D is present.

• Absorption of Monosaccharides, Amino Acids, Dipeptides, Tripeptides, Lipids, Electrolytes, Vitamins, and Water

  • Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
  • The fat soluble vitamins A, D, and E are absorbed in the upper small intestine.
  • The factors that cause malabsorption of fat can also affect absorption of these vitamins.
  • If intrinsic factor is missing, then Vitamin B12 is not absorbed and pernicious anemia results.
  • Of the water soluble vitamins, transport of Folate and B12 across the apical membrane are Na+ independent, but the other water soluble vitamins are absorbed by Na+ co-transporters.