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.
Vitamin D is found in some foods, but the main sources are vitamin D-fortified milk 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 in the kidneys and the liver, and the final product is vitamin D.
Vitamin D's functions:
In children with low vitamin D levels, the supplement can improve bone mineral density. While the evidence does not give a clear answer, it has also been suggested that vitamin D supplementation may reduce the risk of osteoporosis and seasonal flu in children, and high blood pressure and some forms of cancer.
Vitamin D has also been found to improve pain symptoms in patients with low vitamin D levels.
Here are the guidelines for vitamin D intake:
|Age Group||Recommended Dietary Allowance or Adequate Intake (IU/Day)|
|Pregnant or nursing women||600|
IU: international units
The American Academy of Pediatrics recommends supplementation for all children who do not receive at least 400 IU of vitamin D daily. Breastfed babies may require a supplement within the first few days of life. Bottle-fed babies who do not consume enough vitamin-D fortified formula may also need the supplement, as well as any child who does not get plenty of vitamin D in their diet.
As seen above, requirements for pregnant women are the same as for healthy adults, though some believe that pregnant mothers should take more vitamin D than recommended. Furthermore, some experts believe that people at highest risk for vitamin D deficiency, such as older adults or those with limited sun exposure during the winter months, should take 1,000 IU or more daily. However, since the risk of vitamin D toxicity increases with higher doses, such recommendations ought to be discussed individually with a physician.
Symptoms of overt vitamin D deficiency are rare today, but can include the following:
More mild vitamin D deficiency is thought to be relatively common, especially in higher latitudes, and may lead to increased risk of osteoporosis.
Since vitamin D is stored in the body and not excreted in the urine like most water-soluble vitamins, it is possible for it to accumulate and reach toxic levels. Here are safe upper level intakes for vitamin D:
|Age Group||Upper Level Intake (IU/Day)|
|9 years and older||4,000|
|Pregnant or nursing women||4,000|
Symptoms of toxicity:
It is unlikely for sunlight and diet to cause vitamin D toxicity.
If you have problems with any symptoms related to vitamin D toxicity, take less vitamin D supplements.
Fortified foods provide the most vitamin D. Examples of foods that may be fortified with vitamin D are:
There are not many foods that are natural sources of vitamin D. Of those foods that have vitamin D naturally are (most to least):
A relatively small amount of sun exposure can provide adequate vitamin D. In a study of naval personnel in submarines, six days of sun exposure proved capable of supplying enough vitamin D for 49 sunless days. However, the actual synthesis of vitamin D through sunlight is affected by season, latitude, time of day, cloud cover, smog, use of sunblock, and skin pigmentation.
The following populations may be at risk for vitamin D deficiency and may require a supplement:
Here are tips to help increase your intake of vitamin D:
Academy of Nutrition and Dietetics
Office of Dietary Supplements
Bischoff-Ferrari HA, Willett WC, Wong JB, et al. Fracture prevention with vitamin D supplementation. JAMA. 2005;293(18):2257-64.
Calcium and vitamin D for treatment and prevention of osteoporosis. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated June 25, 2013. Accessed October 1, 2013.
Duplessis CA, Harris EB, Watenpaugh DE, et al. Vitamin D supplementation in underway submariners. Aviat Space Environ Med. 2005;76:569-75.
Vitamin D. Office of Dietary Supplements. National Institutes of Health website. Available at: http://ods.od.nih.gov/factsheets/vitamind.asp. Updated June 24, 2013. Accessed October 1, 2013.
Vitamin D intake and supplementation. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated June 25, 2013. Accessed October 1, 2013.
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.
4/5/2010 DynaMed's Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010;91(5):1255-1260.
2/11/2011 DynaMed's Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Winzenberg T, Powell S, Shaw KA, Jones G. Effects of vitamin D supplementation on bone density in healthy children: systematic review and meta-analysis. BMJ. 2011;342.
7/28/2011 DynaMed's Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Bjelakovic G, Gluud LL, Nikolova D, et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst Rev. 20116;(7):CD007470.
3/6/2013 DynaMed's Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Schreuder F, Bernsen RM, van der Wouden JC. Vitamin D supplementation for nonspecific musculoskeletal pain in non-Western immigrants: a randomized controlled trial. Ann Fam Med. 2012 Nov-Dec;10(6):547-55.
Last reviewed October 2013 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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