Vitamin D Test

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Vitamin D Test

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General Description

The Vitamin D Test is a serum assay that quantitates 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 metabolites. The metabolite 25-hydroxyvitamin D is the major circulating form of vitamin D in the body and the best indicator of a patient’s true vitamin status due to its long half-life of 2-3 weeks. The major biologic function of vitamin D is to maintain the normal blood levels of calcium and phosphorus involved in bone mineralization. Vitamin D also influences expression of more than 2,000 genes, including those responsible for regulation of cellular proliferation, cell differentiation, apoptosis, and angiogenesis. The immune-modulating effects of vitamin D are profound, as evidenced by the many conditions which are associated with vitamin D deficiency. The range for adequate serum vitamin D is generally agreed upon in the literature.

Click here to view the Recommendations By Disorder Chart (PDF)

Introduction to Vitamin D

Vitamin D deficiency has been linked to increased risk for many common and serious diseases, including some common cancers, diabetes, cardiovascular disease, and osteoporosis. Deficiency is also prevalent in infants who are solely breastfed and who do not receive vitamin D supplementation. Adults of all ages who have darker skin (increased skin melanin) or who always wear sun protection or limit their outdoor activities, such as homebound elderly persons, are also prone to vitamin D deficits.

Studies suggest that exposure to sunlight, which enhances the production of vitamin D in the skin, prevents many chronic diseases. Most people receive substantial vitamin D through sunlight exposure. Vitamin D can also come from supplementation and diet; however, there are very few foods that naturally contain vitamin D. Some foods that contain vitamin D are fatty fish, fish liver oil, and eggs.

The Vitamin D Test can help to determine if sun exposure is adequate, if dietary vitamin D is sufficient, and to assess the likelihood of malabsorption or liver disease.

Recommended for the following disorders and diseases

	Cardiovascular disease including stroke & hypertension
	Cancer, especially prostate
	Osteoporosis/osteomalacia
	Low blood calcium levels
	Chronic bone/muscle/joint pain
	Periodontal disease
	Diabetes type I & II
	Inflammatory bowel diseases
	Rheumatoid arthritis
	Other autoimmune diseases (multiple sclerosis)
	Chronic fatigue
	Depression & mood disorders
	Schizophrenia
	Cognitive impairment in seniors
	Birth defects

Biological Functions of Vitamin D

The Vitamin D Receptor (VDR) is a nuclear hormone receptor that is activated by the active form of vitamin D, calcitrol. VDR is expressed by most cells in every organ of the body. More than 2,000 genes are regulated by VDR activation.

The primary role of vitamin D is to regulate blood levels of calcium and phosphorus by promoting absorption in the intestines and reabsorption in kidneys. Calcium and phosphorus levels are important for bone mineralization and growth as well as for the prevention of hypocalcemic tetany. Vitamin D is also an important immune regulator. It promotes phagocytosis, anti-tumor activity, and immunomodulary functions that play a role in autoimmune disease. Additionally, vitamin D regulates cellular proliferation, differentiation, apoptosis and angiogenesis.

Vitamin D Deficiency By Population

The 2000-2004 NHANES provided the most recent data on the vitamin D nutritional status of the U.S. population. Approximately 9% of the pediatric population, representing 7.6 million US children and adolescents, were 25(OH)D deficient and 61%, representing 50.8 million US children and adolescents, were 25(OH)D insufficient. Generally, younger people had higher vitamin D levels than older people, males had higher levels than females, and non-Hispanic whites had higher levels than Mexican Americans, who in turn had higher levels than non-Hispanic blacks. Depending on the population group, 1-9% had levels <11 ng/mL , 8-36% had levels <20 ng/mL, and the majority (50-78%) had levels <30 ng/mL.

Indications For Vitamin D Testing

	Patients diagnosed with any of the vitamin D related diseases (cancer, diabetes, hypertension, heart disease, multiple sclerosis, systemic lupus erythematosus, depression, Alzheimer’s, Parkinson’s, epilepsy, and other diseases)
	Patients with osteoporosis or rickets
	Persistent and nonspecific musculoskeletal pain
	Signs of depression or lack of energy
	Patients with gastrointestinal disease and/or who have had a cholecystectomy
	Elderly individuals
	Overweight individuals with a BMI >25
	Infants that are exclusively breastfed or children without a well-balanced diet
	Individuals taking vitamin D supplementation greater than 50 mcg (2,000 IUs) per day
	Individuals that reside above 42 degrees north latitude (a line approximately between the northern border of California and Boston)
	Individuals with medium to dark complexions or who do not regularly receive 20 minutes of direct sunlight each day