Vitamin D

Written by Dale Kiefer | Published on July 25, 2012
Medically Reviewed by George Krucik, MD

What is Vitamin D?

Vitamin D, often called the “sunshine vitamin,” is an important nutrient. Its active form, called calcitriol, behaves like a hormone in the body. The body can produce 10,000 IU or more of vitamin D with little as 10 to 15 minutes of exposure to summer sunlight.

Vitamin D plays a crucial role in supporting and maintaining bone health. There are few natural food sources that contain vitamin D. Food manufacturers began fortifying milk and other products with vitamin D decades ago, aimed to wipe out rickets, a childhood bone disease.

Receptors for this important hormone are found in virtually every type of cell and tissue in the body. Receptors work like locks: the lock turns when the right key is inserted, prompting the cell to act in a certain way. Evidence shows that people with higher levels of vitamin D may live longer. Studies also suggest that a majority of Americans have insufficient or deficient levels of vitamin D.

Why Do You Need Vitamin D?

The presence of vitamin D receptors throughout the body hints at the importance of the vitamin. Research shows that vitamin D plays a crucial role in the health of the immune system, brain, heart and blood vessels, among other organs and systems.

Many doctors now monitor their patients’ vitamin D levels and prescribe supplemental vitamin D when levels are too low. A lack of vitamin D may increase your risk of developing numerous diseases and conditions.

Autoimmune diseases—such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis—may be linked to a vitamin D deficiency. Autoimmune diseases occur when the immune system attacks the body’s own tissues. Too little vitamin D has been linked to poor immune system function.

Vitamin D deficiency is also linked to a risk for type 2 diabetes, osteoporosis (a condition that results in brittle bones), heart disease, mood disorders, and even certain types of cancer. The active form of vitamin D helps control chronic inflammation. Ongoing inflammation has been linked to diseases such as hardening of the arteries (atherosclerosis), arthritis (painful, inflamed joints), and even cancer.

Supplementation Recommendations

Vitamin D may be taken as a supplement. Two forms are available: vitamin D3 and vitamin D2. Vitamin D3 is preferable, as it is better absorbed when taken by mouth.

Current government recommended dietary allowances for vitamin D range from 400 IU to 800 IU daily. Many experts argue that higher daily intakes than what’s recommended are required to achieve better health outcomes. Some experts even recommend taking 2,000 to 7,000 IU of vitamin D3 everyday.

Vitamin D Deficiency

The following factors can affect your vitamin D levels:

  • exposure to sunlight
  • the use of sunscreens
  • body mass
  • skin color
  • diet

People with dark skin don’t make vitamin D as easily as light-skinned people when exposed to sunlight.

Vitamin D dissolves in fat, and is stored in fat cells. Overweight people tend to have more vitamin D stored in fat rather than circulating in the blood. They may require higher doses of vitamin D3 to maintain optimal serum levels.

Vitamin D Toxicity

Vitamin D toxicity, resulting from taking too much supplemental vitamin D, is relatively rare. The amount of supplemental vitamin D needed to cause vitamin D toxicity is more than 10,000 IU per day, taken every day for months. The Tolerable Upper Intake Levels published by the U.S. government range from 1,000 IU per day for infants to 4,000 IU per day for adults. This amount is considered too conservative by some experts.

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Article Sources:

  • No authors listed] Vitamin D. Monograph. Altern Med Rev. 2008 Jun;13(2):153-6
  • Calvo MS, Whiting SJ, Barton CN. Vitamin D fortification in the United States and Canada: current status and data needs. Am J Clin Nutr. 2004 Dec;80(6 Suppl):1710S-6S.
  • de Boer IH, Levin G, et al. Serum 25-hydroxyvitamin d concentration and risk for major clinical disease events in a community-based population of older adults: a cohort study. Ann Intern Med. 2012 May 1;156(9):627-34.
  • Giovannucci E. Can vitamin D reduce total mortality? Arch Intern Med. 2007 Sep 10;167(16):1709-10.
  • Hewison M. Vitamin D and immune function: Autocrine, paracrine or endocrine? Scand J Clin Lab Invest Suppl. 2012;243:92-102.
  • Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81.
  • Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  • Rickets. (2010, Oct. 14) Mayo Clinic. Retrieved on May 14, 2012, from http://www.mayoclinic.com/health/rickets/DS00813
  • Simon KC, Munger KL, Ascherio A. Vitamin D and multiple sclerosis: epidemiology, immunology, and genetics. Curr Opin Neurol. 2012 Jun;25(3):246-51.
  • Tripkovic L, Lambert H, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012 May 2. [Epub ahead of print]
  • Vieth R, Bischoff-Ferrari H, et al. The urgent need to recommend an intake of vitamin D that is effective. Am J Clin Nutr. 2007 Mar;85(3):649-50.
  • Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988 Aug;67(2):373-8.

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