Vitamin D (25-Hydroxy)
Understanding Vitamin D (25-Hydroxy)
What is Vitamin D (25-Hydroxy)?
The Vitamin D (25-Hydroxy) test measures the level of 25-OH 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 a fat-soluble essential nutrient. It exists in two primary forms. Vitamin D3 (Cholecalciferol) derived from animal sources and vitamin D2 (Ergocalciferol) derived from plant sources; both performing similar functions. The main sources of vitamin D3 are certain foods, dietary supplements, and exposure to ultraviolet B (UVB) radiation from sunlight, while vitamin D2 is derived from products or supplements of plant origin and mushrooms etc. Both these forms are converted into 25-hydroxy D2 or D3 respectively in the liver. The levels of 25-hydroxy Vitamin D in blood is considered the best parameter to assess vitamin D status of the body. The Vitamin D (25-OH) test measures only the Total 25-OH D vitamin (i.e D2+D3) and does not differentiate between the two forms.
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. The Vitamin D (25-Hydroxy) test 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 the 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?
The 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?
The 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 levels of 25-hydroxy Vitamin D in blood is considered the best parameter to assess vitamin D status of the body. A Vitamin D (25-Hydroxy) measures the level of Total 25-OH vitamin D (D2+D3) , but it does not differentiate between the two forms as it is the major 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 is the vitamin D test used for?
Q. What are the signs and symptoms of low vitamin D levels?
Q. How much vitamin D is needed daily?
Q. What are the causes of vitamin D deficiency?
Q. What is the right time to get the vitamin D test done?
Q. Are there any risks associated with the vitamin D test?
Q. Who should be tested for vitamin D?
Q. What are some of the common vitamin D benefits for the body?
Q. What are some of the easily available vitamin D food sources for vegetarians?
Q. What are the additional lab tests needed to be performed in case of abnormal vitamin D test results?
Q. What are some of the common side effects of vitamin D overdose?
Q. What is osteomalacia?
Q. What are the sources of vitamin D?
Q. What is osteoporosis?
Q. Is there any correlation between the nutrients vitamin D and calcium?
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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