Functions of Vitamin D1

From: Holick, Michael.  Am J Clin Nutr 2004;79:362–71.

Vitamin D is a fat soluble vitamin synthesized from cholesterol by the skin where it is exposed to ultra-violet B radiation (sun exposure).  Once vitamin D is synthesized it is altered by the liver and kidney into its active form.  Small amounts are obtained from dietary sources.  Recent research points to a vitamin D deficiency epidemic in the U.S.  Sunscreens (to include make-up) with an SPF (sun protection factor) of greater than 8 inhibit the synthesis of vitamin D.  Not only is vitamin D necessary to maintain normal calcium levels, but it helps with the maintenance of  the neuromuscular system and the immune system.  In addition, vitamin D has genetic effects by regulating cell growth and differentiation.  Some vitamin D deficiency associated diseases include rickets, osteomalacia, osteoporosis, and cancer.  Recently, new research has identified vitamin D playing a role in the prevention of diabetes.  Vitamin D is a very safe and effective treatment to use in lieu of the flu shot.

Signs & Symptoms of Deficiency:

  • Poor immune function
  • bow legs (softening or malformation of the bones)
  • Muscle pain
  • Muscle weakness
  • Poor growth
  • Skin lesions (eczema)
  • Acne
  • Chronic infection
  • Sinus infections

Vitamin D has been shown to be beneficial in the following conditions:

  • Cancer
  • High blood pressure
  • Type I and Type II Diabetes
  • Osteoporosis
  • Rickets
  • Osteomalacia
  • Autoimmune diseases
  • Multiple Sclerosis

Drugs or additives that may deplete or interfere with Vitamin D metabolism:

  • Alcohol
  • Corticosteroids
  • Olestra (a food additive found in many fat free products)
  • Mineral oil (when taken consistently in higher doses)
  • Cholestyramine
  • Colesevelam (Welchol)
  • Colestipol
  • Statin medications – Although these medications have not been shown to directly decrease vitamin D levels in research studies, they inhibit cholesterol synthesis which could potentially effect vitamin D production.
  • Long term therapy with anti-convulsant medications is thought to interfere with the liver and kidneys ability to activate vitamin D.
  • Isoniazid and Rifampicin (Antibiotics) are also thought to interfere with the liver and kidneys ability to activate vitamin D.

Laboratory testing for Vitamin D:

  • 25 OH-D is the most accurate way to measure this nutrient
  • Lymphocyte proliferation assays (Spectracell labs)

Food Sources:

  • Sunlight is the best source of natural vitamin D.  However; the following foods also contain some vitamin D – Liver, cod liver oil, herring, salmon, mackerel, sardines, tuna, eggs, andfortified dairy products.

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