To determine if you have a vitamin D deficiency; if you are receiving vitamin D supplementation, to determine if it is adequate
When you have an abnormal calcium, phosphorus, and/or parathyroid hormone level; when you have evidence of bone disease or bone weakness; when you are at high risk of deficiency or a healthcare practitioner suspects that you might have a vitamin D deficiency; prior to starting drug treatment for osteoporosis; periodically to monitor treatment of vitamin D deficiency
A blood sample drawn from a vein in your arm
Vitamin D is a family of compounds that is essential for the proper growth and formation of teeth and bones. This test measures the level of vitamin D in the blood.
Two forms of vitamin D can be measured in the blood, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. The 25-hydroxyvitamin D is the major form found in the blood and is the relatively inactive precursor to the active hormone, 1,25-dihydroxyvitamin D. Because of its long half-life and higher concentration, 25-hydroxyvitamin D is commonly measured to assess and monitor vitamin D status in individuals.
Vitamin D comes from two sources: endogenous, which is produced in the skin on exposure to sunlight, and exogenous, which is ingested in foods and supplements. The chemical structures of the types of vitamin D are slightly different, and they are named vitamin D2 (ergocalciferol, which comes from plants) and vitamin D3 (cholecalciferol, which comes from animals). The D2 form is found in fortified foods and in most vitamin preparations and supplements. Vitamin D3 is the form produced in the body and is also used in some supplements. Vitamin D2 and D3 are equally effective when they are converted by the liver and the kidney into the active form, 1,25-dihydroxyvitamin D.
Some tests do not distinguish D2 and D3 forms of the vitamin and report only the total result. Newer methods, however, may report levels of both D2 and D3 and then add them together for a total level.
The main role of vitamin D is to help regulate blood levels of calcium, phosphorus, and (to a lesser extent) magnesium. Vitamin D is vital for the growth and health of bone; without it, bones will be soft, malformed, and unable to repair themselves normally, resulting in diseases called rickets in children and osteomalacia in adults. Vitamin D has also been shown to influence the growth and differentiation of many other tissues and to help regulate the immune system. These other functions have implicated vitamin D in other disorders, such as autoimmunity and cancer.
Based on data from the National Health and Nutrition Examination Survey, the Centers for Disease Control and Prevention (CDC) reports that two-thirds of U.S. population has sufficient vitamin D, while roughly one-quarter are at risk of inadequate vitamin D and 8% are at risk of deficiency, as defined by the Dietary Reference Intake (DRI) set by the Institute of Medicine.
People at higher risk of deficiency include the elderly or obese people, people who don't get enough sun exposure, people with darker skin, and people who take certain medications for long periods of time. Adequate sun exposure is typically estimated to be two periods per week of 5-20 minutes. People who do not have adequate sun exposure may obtain the vitamin D that they need from food sources or supplements.
A vitamin D test is used to:
When calcium is low and/or a person has symptoms of vitamin D deficiency, such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia), 25-hydroxyvitamin D usually is ordered to identify a possible deficiency in vitamin D.
The test may be requested when an individual is known to be at risk of vitamin D deficiency. Older adults, people who are institutionalized or homebound and/or have limited sun exposure, those who are obese, who have undergone gastric bypass surgery, and/or who have fat malabsorption are at an increased risk of a vitamin D deficiency. Also included in this group are people with darker skin and breastfed infants.
25-hydroxyvitamin D is often requested before an individual begins drug therapy for osteoporosis.
This testing may be ordered when kidney disease or abnormalities of the enzyme that converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D is suspected. Rarely, this test may be done when calcium is high or a person has a disease that might produce excess amounts of vitamin D, such as sarcoidosis or some forms of lymphoma (because immune cells may make 1,25-dihydroxyvitamin D).
When vitamin D, calcium, phosphorus, or magnesium supplementation is necessary, vitamin D levels are sometimes measured to monitor treatment effectiveness.
Although there are differences among vitamin D methods, most laboratories utilize similar reference intervals. Because toxicity is rare, the focus has been on the lower limit and what cut-off for total 25-hydroxyvitamin D (D2 + D3) indicates deficiency.
A low blood level of 25-hydroxyvitamin D may mean that a person is not getting enough exposure to sunlight or enough dietary vitamin D to meet his or her body's demand or that there is a problem with its absorption from the intestines. Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.
There is some evidence that vitamin D deficiency may increase the risk of some cancers, immune diseases, and cardiovascular disease.
A high level of 25-hydroxyvitamin D usually reflects excess supplementation from vitamin pills or other nutritional supplements.
A low level of 1,25-dihydroxyvitamin D can be seen in kidney disease and is one of the earliest changes to occur in persons with early kidney failure.
A high level of 1,25-dihydroxyvitamin D may occur when there is excess parathryoid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make 1,25-dihydroxyvitamin D outside of the kidneys.
High levels of vitamin D and calcium can lead to the calcification and damage to organs, particularly the kidneys and blood vessels.
If magnesium levels are low, they can cause a low calcium level that is resistant to vitamin D and parathyroid hormone regulation. It may be necessary to supplement both magnesium and calcium to regain normal function.
It depends on your age and sex. In 2010, the Institute of Medicine set the Dietary Reference Intake (DRI) for both calcium and vitamin D. For details, see the report: DRIs for Calcium and Vitamin D.
Yes. The amount of vitamin D produced by the body may be insufficient, especially when there is limited exposure to sunlight and routine use of sunscreens. Since dietary vitamin D is found naturally only in a few foods, such as cod liver oil, dietary intake would not be sufficient for most people. However, in the United States, vitamin D is routinely added to milk, fortified cereals, and fruit juices to ensure adequate dietary availability. Fortification of milk and infant formula has been a real success story in the United States, drastically reducing the rate of juvenile rickets and making it a relatively rare occurrence.
Maybe. Although all milk is fortified, many dairy products are not, or are to a lesser extent.
Yes, there is a topical form of vitamin D cream that is used to treat psoriasis. Research is being done in other areas, including the potential use of vitamin D to help control autoimmune conditions.
Since absorption of calcium is dependent on vitamin D, many manufacturers of calcium supplements add vitamin D to assure optimal calcium uptake. If you have adequate amounts of vitamin D from other sources, the additional vitamin D is not necessary. The amount of vitamin D in these tablets is not likely to lead to excess vitamin D or be harmful either.
Sources Used in Current Review
(2011) National Institute of Health MedlinePlus. New Recommended Daily Amounts of Calcium and Vitamin D. Available online at https://www.nlm.nih.gov/medlineplus/magazine/issues/winter11/articles/winter11pg12.html. Accessed July 9, 2016.
(Feb 2016) National Institute of Health Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals. Available online at https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed July 9, 2016.
(June 2011) Holick, N. et al. Evaluation, Treatment and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. Available online at http://press.endocrine.org/doi/full/10.1210/jc.2011-0385. Accessed July 9, 2016.
(Oct 2015) Tangpricha, V. Vitamin D Deficiency and Related Disorders. Medscape. Available online at http://emedicine.medscape.com/article/128762-overview#a6. Accessed July 9, 2016.
(Feb 2016) University of Maryland Medical Center. Vitamin D. Available online at http://umm.edu/health/medical/altmed/supplement/vitamin-d. Accessed July 9, 2016.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
NIH (2001 August 07, Updated). Vitamin D. NIH Clinical Center, National Institutes of Health. Facts About Dietary Supplements [On-line information]. Available online at http://www.cc.nih.gov/ccc/supplements/vitd.html.
Oltikar, A. (2001 February 09). Vitamin D. MedlinePlus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002405.htm.
Conlan, R. & Sherman, E., et. al (2001). UNRAVELING THE ENIGMA OF VITAMIN D. The National Academies, National Academy of Sciences Beyond Discovery, The path from research to human benefit [On-line Journal]. Available online at http://www.beyonddiscovery.org/content/view.article.asp?a=414.
Vitamin D Home Page. About Vitamin D. University of California, Riverside, Vitamin D Home Page [On-line information]. Available online at http://vitamind.ucr.edu/about.html.
DeLuca, H. (2001 January 18, Updated). Vitamin D. Linus Pauling Institute [On-line information]. Available online at http://www.orst.edu/dept/lpi/infocenter/vitamins/vitaminD/.
Miller-Keane Medical Dictionary (2000). Vitamin. WebMDHealth, Dictionary [On-line information]. Available online at http://my.webmd.com/content/asset/miller_keane_35600.
Merck. Vitamins and Minerals. The Merck Manual of Medical Information--Home Edition [On-line information]. Available online at http://www.merck.com/pubs/mmanual_home/sec12/135.htm.
Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Henry JB, ed. New York: Saunders: 2006.
(November 2006) Quest Diagnostics. Vitamin D, 25-Hydroxy, Test Summary (online information). Available online at http://www.questdiagnostics.com/hcp/topics/endo/vitamin_d.html.
(November 2006) ARUP Laboratory. Vitamin D, 25-Hydroxy, Test Directory (online information). Available online at http://www.aruplab.com/guides/ug/tests/0070277.jsp.
Saenger AK, et al. Quantification of Serum 25-Hydroxyvitamin D2 and D3 Using HPLC-Tandem Mass Spectrometry and Examination of Reference Intervals for Diagnosis of Vitamin D Deficiency. American Journal of Clinical Pathology 2006;125:914-920.
Utiger RD. The Need for More Vitamin D. New England Journal of Medicine 1998; 33:828-829.
Mayo Medical Laboratories. Vitamin D Testing. Available online at http://www.mayomedicallaboratories.com/articles/vitamind/index.html. Accessed February 2009.
National Osteoporosis Foundation. Prevention, Vitamin D. Available online at http://www.nof.org/prevention/vitaminD.htm. Accessed February 2009.
Bikle D. Nonclassic Actions of Vitamin D. J Clin Endocrinol Metab 2009; 94: 26-34.
Mark S, Gray-Donald K, Delvin EE, O'Loughlin J, Paradis G, Levy E, Lambert M. Low vitamin D status in a representative sample of youth from Quebec, Canada. Clinical Chemistry 2008 Aug; 54(8): 1283-9.
Topiwala, S. (Updated 2012 July 19). 25-hydroxy vitamin D test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003569.htm. Accessed February 2013.
Rennert, N. (Updated 2011 December 11). Hypervitaminosis D. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001594.htm. Accessed February 2013.
Tangpricha, V. and Khazai, N. (Updated 2012 December 10). Vitamin D Deficiency and Related Disorders. Medscape Reference. [On-line information]. Available online at http://emedicine.medscape.com/article/128762-overview. Accessed February 2013.
Nguyen, H. and Chernoff, A. (Updated 2012 April 20). Vitamin D3 25-Hydroxyvitamin D. Medscape Reference. [On-line information]. Available online at http://emedicine.medscape.com/article/2088694-overview#showall. Accessed February 2013.
Nguyen, H. and Chernoff, A. (Updated 2012 April 20). Vitamin D3 1,25-Dihydroxyvitamin D. Medscape Reference. [On-line information]. Available online at http://emedicine.medscape.com/article/2088672-overview#showall. Accessed February 2013.
(2011 September). Vitamin D Insufficiency. Mayo Clinic Mayo Medical Laboratories Communique. [On-line information]. Available online at http://www.mayomedicallaboratories.com/articles/communique/2011/09.html. Accessed February 2013.
Johnson, L. (Revised 2012 December). Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed February 2013.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 1040-1043.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 529-530.
McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 105-106.
Press release. IOM Report Sets New Dietary Intake Levels for Calcium and Vitamin D To Maintain Health and Avoid Risks Associated With Excess. Institute of Medicine. Available online at http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=13050. Issued November 30, 2010. Accessed March 2010.
Report at a Glance. DRIs for Calcium and Vitamin D. Institute of Medicine. Available online at http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/DRI-Values.aspx. Published November 30, 2010. Accessed March 2010.
(March 2011) Centers for Disease Control and Prevention. Vitamin D Status, United States, 2001-2006. Available online at http://www.cdc.gov/nchs/data/databriefs/db59.htm#ref1. Accessed March 2013.
Holick MF et al. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 96(7): 1911 (July 1, 2011). Available online at http://dx.doi.org/10.1210/jc.2011-0385. Accessed May 2013.