Vitamin D (25-Hydroxy)
Understanding Vitamin D (25-Hydroxy)
What is Vitamin D (25-Hydroxy)?
A Vitamin D (25-Hydroxy) test measures the level of vitamin D in the body. Vitamin D is a fat-soluble essential nutrient that helps the body absorb calcium & phosphorus to maintain strong bones & teeth and to have a healthy immune system. Vitamin D levels are a valuable indicator of many bone-related problems, such as rickets, osteomalacia, and osteoporosis.
Vitamin D is vital to many bodily functions, including immune system regulation, maintenance of bone health, and cell growth. It is also a multifunctional hormone that regulates the levels of nutrients like calcium and phosphorus. Vitamin D can be obtained from healthy exposure to sunlight. Additionally, dietary sources such as fortified foods, green vegetables, mushrooms, egg yolks, fatty fish, and vitamin D supplements can help the body maintain healthy levels of this nutrient.
As per an NCBI (National Center for Biotechnology Information) study, vitamin D deficiency is highly prevalent across all age groups in India. Insufficient vitamin D levels can increase susceptibility to fractures, weakened muscles, fatigue, compromised immune function, and a higher likelihood of chronic illnesses like diabetes. A Vitamin D (25-Hydroxy) examination can aid in assessing whether your body has an inadequate supply (deficiency) or an excessive amount of vitamin D, often resulting from excessive supplement intake. If such circumstances arise, it may be necessary to discontinue vitamin D supplements and seek medical advice.
Usually, no special preparation is required for this test; you may consume a regular diet before taking the test. However, it is generally recommended to stop taking vitamin D supplements before a Vitamin D (25-Hydroxy) test, as these supplements may affect the accuracy of the test results.
Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific test results. The test results will help them determine your medical condition, make recommendations for lifestyle modifications such as diet and exercise, prescribe medication if required to manage your condition, and formulate your overall treatment plan.
What is Vitamin D (25-Hydroxy) used for?
A Vitamin D (25-Hydroxy) test can be done:
- To determine deficient, insufficient, or toxic vitamin D levels in the body.
- For routine checkups in individuals at high risk of vitamin D deficiency. The risk of vitamin D deficiency increases with obesity, limited sun exposure, weight loss surgery, digestive disorders like Crohn’s disease, kidney or liver disease, and the use of certain medicines like phenytoin.
- In individuals with vitamin D deficiency symptoms, such as bone deformities, immune system dysfunction, muscle cramps, and dental abnormalities.
- To monitor the adequacy of treatment in patients who are receiving vitamin D supplements.
- To diagnose/monitor problems with the functioning of the parathyroid gland since the parathyroid hormone (PTH) is essential for vitamin D metabolism.
What does Vitamin D (25-Hydroxy) measure?
A Vitamin D (25-Hydroxy) test measures the levels of vitamin D in the body. It is an essential nutrient that can be synthesized in the body upon healthy exposure to sunlight or absorbed from dietary sources. It majorly exists in two forms: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). Vitamin D2 is present in plants, such as yeast or mushrooms, and is available as a supplement in fortified foods, and vitamin D3 is found in foods like cheese, green vegetables, mushrooms, egg yolks, and fatty fish.
Both forms of vitamin D (D2 and D3) need to undergo some chemical changes before being available for use in the body. These chemical changes take place in the liver or kidneys. The liver converts vitamin D to 25-hydroxyvitamin D (25-OH vitamin D). A Vitamin D (25-Hydroxy) test measures the level of this 25-OH vitamin D as it is the primary form of vitamin D that circulates in the blood.
Interpreting Vitamin D (25-Hydroxy) results
Interpretations
A lower vitamin D level than the normal reference range indicates vitamin D deficiency, which can be because of less sun exposure, dietary lack, or decreased absorption from the intestine.
A higher vitamin D level than the normal reference range indicates vitamin D intoxication, usually due to excess vitamin supplementation.
Range:
The vitamin D range is measured as nanograms per milliliter (ng/mL) or nmol/L and can vary from lab to lab.
|
Level |
Reference range (ng/mL) |
|
Deficiency |
<20 |
|
Insufficiency |
20-29 |
|
Sufficiency |
30-100 |
|
Toxicity |
>100 |
Note:
- This test does not include a separate vitamin D2 and D3 level analysis.
- There can be seasonal variation in 25 (OH) vitamin D levels, with values being 40-50% lower in winter than in summer. It is also influenced by sunlight, latitude, skin pigmentation, sunscreen use, and hepatic function.
- 25 (OH) vitamin D levels can vary with age.
- 25 (OH) vitamin D level is increased during pregnancy.
Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Vitamin D (25-Hydroxy)
Frequently Asked Questions about Vitamin D (25-Hydroxy)
Q. What are the signs and symptoms of low vitamin D levels?
Q. How much vitamin D is needed daily?
Q. What is the right time to get a vitamin D test done?
Q. Are there any risks associated with a vitamin D test?
Q. What can cause vitamin D deficiency?
Q. Who should be tested for Vitamin D?
Q. What are the additional lab tests needed to be performed in case of abnormal Vitamin D test results?
Q. What is osteomalacia?
Q. What are the sources of Vitamin D?
Q. What is osteoporosis?
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References
- Vitamin D [Internet]. NIH; 12 Aug. 2022 [Accessed 11 Mar. 2023]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Aparna P, Muthathal S, Nongkynrih B, Gupta SK. Vitamin D deficiency in India. J Family Med Prim Care. 2018 Mar-Apr;7(2):324-330. [Accessed 11 Mar. 2023]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6060930/
- Vitamin D [Internet]. Boston, USA: Harvard T.H. Chan; March 2023 [Accessed 11 Mar. 2023]. Available from: https://www.hsph.harvard.edu/nutritionsource/vitamin-d/
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