Definition

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.

Causes

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 medications that affect the process of converting vitamin D to a form that the body can use, such as:
  • Anti-seizure medications
  • Severe liver disease
  • Chronic kidney disease
  • Vitamin-D dependant rickets (an inherited condition)
  • Hypoparathyroidism (underactive parathyroid)
  • Nephrotic syndrome (kidney condition)
  • Peritoneal dialysis

Risk Factors

Risk factors include:

• Limited sun exposure
• Darker skin color
• Kidney disease
• Restricted activity, such as due to hospitalization
• Injury due to a severe burn
• Malabsorption disorder, such as celiac disease
• Obesity
• Certain types of diets, such as macrobiotic diet
• Liver conditions
• Babies who are breastfed or do not consume enough formula that is fortified with vitamin D

Wearing sunscreen may be a risk factor for vitamin D deficiency. But, organizations like the American Academy of Dermatology (AAD) recommend that you use sunscreen to protect your skin from UV exposure, a known risk factor for skin cancer.

Symptoms

If your vitamin D deficiency is mild to moderate, you may not have any symptoms. If you have a severe deficiency, you may experience:

• Bone and muscle pain
• Muscle weakness
• Hip pain
• Fractures
• Difficulty walking, walking up stairs, and getting out of a chair
• Falls

Diagnosis

You will be asked about your symptoms and medical history. A physical exam will be done.

Your bodily fluids may be tested. This can be done with blood tests.

Your bones may be tested. This can be done with bone tests.

Treatment

Talk with your doctor about the best plan for you. Treatment options include:

• Vitamin D supplementation—High doses of vitamin D are given for 6-12 weeks. This is followed by a lower dose of the vitamin. The doses are continued until blood levels return to normal.
• Calcium supplementation—Calcium plus vitamin D supplements may be given to increase D levels. This can also improve bone strength in older women with low vitamin D.
• Light therapy—Exposure to sunlight or UV radiation can increase D levels. Vitamin D3 is produced in the skin when it is exposed to these light sources.

Prevention

To prevent vitamin D deficiency, take these steps:

• Eat a healthy diet. Foods are not naturally high in vitamin D. Many foods are enriched with vitamin D, such as milk, juices, and cereal.
• Take a vitamin D supplement if recommended by your doctor. Your baby may need a supplement if he is breastfed or does not consume enough formula that is fortified with vitamin D. Children may also need to take a supplement if they are not getting enough vitamin D in their diets.
• Follow your doctor’s guidelines on getting enough sun exposure.
• If you or a family member has any of the above risk factors, talk to the doctor about other ways to avoid becoming deficient in vitamin D.

Office of Dietary Supplements—National Institutes of Health http://ods.od.nih.gov

Health Canada http://www.hc-sc.gc.ca

American Academy of Dermatology. Position statement on vitamin D. American Academy of Dermatology website. Available at:
http://www.aad.org/Forms/Policies/Uploads/PS/PS-Vitamin%20D.pdf
Updated November 14, 2009. Accessed December 22, 2014.

Dietary supplement fact sheet: vitamin D. Office of Dietary Supplements website. Available at:
http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Updated November 10, 2014. Accessed December 22, 2014.

Pfeifer M, Begerow B, et al. Vitamin D and muscle function. Osteoporosis Int. 2002;13:187-194.

Plotnikoff GA, Quigley JM. Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific musculoskeletal pain. Mayo Clin Proc. 2003; 78:1463.

Tangpricha V, Pearce EN, et al. Vitamin D insufficiency among free-living healthy young adults. Am J Med. 2002;112:659-662.

Vitamin D deficiency in adults. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated October 26, 2014. Accessed December 22, 2014.

Wagner CL, Greer FR, American Academy of Pediatrics Section on Breastfeeding, American Academy of Pediatrics Committee on Nutrition. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122:1142-1152.