Vitamin D is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body's liver and fatty tissues. Vitamin D acts as both a vitamin and a hormone. Two of the main sources of vitamin D are food and sunlight. The ultraviolet rays of the sun react with cholesterol present on the skin and create previtamin D3. This compound goes through a series of reactions involving the kidneys and the liver. The final product is vitamin D.

Vitamin D deficiency describes low levels of vitamin D in the blood. This condition can lead to a condition known as rickets in children. In adults, it can lead to osteomalacia. These are two forms of bone diseases that weaken bones. It is important to contact your doctor if you think you have vitamin D deficiency.

Weakened Bone
Weakened bone at hip
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Vitamin D deficiency can be caused by:

  • Inadequate intake of vitamin D in the diet
  • Lack of sunlight due to:
    • Having a darker skin color
    • Wearing clothes that cover most of the skin
    • Living in northern latitudes during the winter
    • Not being exposed to direct sunlight—Sunlight through windows, clothes, or sunscreen-covered skin is not enough for the body to synthesize vitamin D.
  • Conditions and procedures that affect the body’s ability to absorb vitamin D from the digestive tract (such as celiac disease, inflammatory bowel disease, bariatric surgery)
  • Conditions or medicines that affect the process of converting vitamin D to a form that the body can use, such as:
    • Anti-seizure medicines such (such as phenobarbital, phenytoin, carbamazepine)
    • Other medicines (such as rifampin, isoniazid, theophylline)
    • Severe liver disease
    • Chronic kidney disease
    • Vitamin-D dependant rickets (an inherited condition)
    • Hypoparathyroidism (underactive parathyroid)
    • Nephrotic syndrome (kidney condition)
    • Peritoneal dialysis