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Vitamin D (25-Hydroxy)

Also referred as

Calcidiol

Vit D (25-OH)

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The Vitamin D (25-Hydroxy) test measures the level of 25-OH vitamin D in the body. Vitamin D helps your body absorb calcium and phosphorus, which are important for strong bones and teeth. It also supports your immune system. This test helps you assess bone health, immunity, and overall well-being.

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Understanding Vitamin D (25-Hydroxy)

Vitamin D is an essential fat-soluble nutrient. It exists in two primary forms:

Vitamin D3 (Cholecalciferol): derived from animal sources, supplements, and made by the skin when you are in sunlight.
Vitamin D2 (Ergocalciferol): derived from plant sources and supplements.

Both vitamin D2 and D3 perform similar functions. Both forms are converted into 25-hydroxy vitamin D D2 or D3 respectively in the liver. The Vitamin D (25-Hydroxy) test checks the total amount of vitamin D in your blood (D2 + D3), but it doesn’t distinguish between the two types.

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 the following conditions:

Fractures
Weakened muscles
Fatigue
Compromised immune function
Higher likelihood of chronic illnesses like diabetes

The Vitamin D (25-Hydroxy) test is done to check if you have health problems that affect how your body uses vitamin D, such as weak bones (osteoporosis), or kidney or liver issues. It is also done if there are risk factors like insufficient sunlight exposure or having a poor diet. It is also used for the diagnosis of causes of rickets and osteomalacia. Additionally, this test is done to monitor vitamin D levels in people who are taking supplements, to ensure their levels stay within a healthy range and are not too low or too high.

Usually, no special preparation is required for this test. You can get this test at any time of the day at your convenience. 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.

Always consult your doctor to understand what your results mean. They can guide you with the right treatment, lifestyle changes, or medication if needed.

Lifestyle Tips to Support Healthy Vitamin D Levels:

☀️ Heliotherapy (Sunlight Exposure): Spend some time outdoors, under the sun (preferably in the morning) to help your body naturally produce vitamin D.

🥙 Eat (Diet): Include vitamin D-rich foods such as eggs, mushrooms, salmon, fortified milk, and orange juice.

🏃 Activity (Exercise): Engage in regular physical activity, especially outdoors, can support better vitamin D synthesis and bone health.

😓 Lifestyle (Stress): Manage stress through relaxation techniques or yoga, as stress can indirectly impact bone health.

👨‍⚕️ Talk to Your Doctor (Consultation): Avoid self-medication and taking high doses of vitamin D supplements without a doctor's advice.

🚭 Habits (Alcohol & Smoking): Limit alcohol and quit smoking, as these can affect vitamin D metabolism and bone strength.

What does Vitamin D (25-Hydroxy) measure?

The Vitamin D (25-Hydroxy) test measures the levels of vitamin D in the body. Vitamin D 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.

Vitamin D is available in two key forms: D2 (present in plants like mushrooms and in some fortified foods) and D3 (present in foods like cheese, green vegetables, egg yolks, mushrooms, and fatty fish).

Both forms of vitamin D need to be converted in the liver and kidneys before the body can use them effectively. This test shows the total level of vitamin D (D2 + D3) circulating in the body and guides your doctor in recommending the right treatment or lifestyle changes if needed.

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FAQs related to Vitamin D (25-Hydroxy)

What is the Vitamin D (25-Hydroxy) test used for?

This test is done to measure the amount of vitamin D in individuals with symptoms such as bone deformities, dysfunction of the immune system, muscle cramps, and dental abnormalities. It is also used to monitor treatment response in individuals who are taking vitamin D supplements.

What are the signs and symptoms of low vitamin D levels?

Bone pain, depression, hair loss, muscle weakness, appetite loss, pale skin, and sleep disturbances are some common signs and symptoms of vitamin D deficiency.

How much vitamin D is needed daily?

a) 0–12 months: 400 IU/day; b). Ages 1–70: 600 IU/day; c) Over 70: 800 IU/day. For adults with low levels (<30 ng/mL), 1,500–2,000 IU/day is advised to restore balance (as per Endocrine Society).

What are the causes of vitamin D deficiency?

Vitamin D deficiency can occur if you do not get enough from sunlight or food if your body cannot absorb vitamin D properly, or if your kidneys are not able to activate it. It occurs more frequently in individuals with milk allergy, lactose intolerance, or vegans and vegetarians.

What is the right time to get the Vitamin D (25-Hydroxy) test done?

The Vitamin D (25-Hydroxy) test can be done at any time of the day. However, you should stop taking vitamin D supplements before the test to get accurate results.

Are there any risks associated with the Vitamin D (25-Hydroxy) test?

No, usually, there are no risks associated with this test. The blood sample is withdrawn with the help of a needle, and the process is fairly fast and relatively painless.

Who should be tested for vitamin D?

Vitamin D 25 (OH) testing is recommended for: a) those being treated for osteoporosis; b) those with low or high calcium levels; c) people with conditions like cystic fibrosis, or Crohn’s disease; d) after gastric bypass surgery; e) if there’s no improvement with vitamin D therapy; f) elderly individuals with low sun exposure; g) breastfed infants; h) people with signs of rickets or soft bones (osteomalacia).

What are some of the common vitamin D benefits for the body?

Vitamin D is essential for strong bones, healthy teeth, and a strong immune system. It helps the body absorb calcium and phosphorus. Low levels can lead to bone problems like rickets, osteomalacia, and osteoporosis.

Which vegetarian foods are rich in vitamin D?

Vegetarian foods that are rich in vitamin D include mushrooms, broccoli, carrots, apples, bananas, rice, whole wheat, milk, cheese, and fortified cereals.

What are the additional lab tests needed to be performed along with the vitamin D test?

Your doctor may recommend additional tests such as serum calcium, serum phosphorus, 24-hour urine calcium, parathyroid hormone (PTH) levels, or bone alkaline phosphatase along with a vitamin D test.

What are the common side effects of vitamin D overdose?

Common side effects of vitamin D overdose include high calcium levels in the blood (hypercalcemia), which can cause symptoms like nausea, vomiting, muscle weakness, tiredness, mood changes, body aches, loss of appetite, dehydration, frequent urination, increased thirst, and kidney stones. In severe cases, excess vitamin D can lead to kidney failure, calcium buildup in soft tissues (such as the heart and blood vessels), irregular heartbeat, and in rare cases, even death.

What is osteomalacia?

Osteomalacia is a condition where bones become soft and weak, mainly because they lose important minerals like calcium. This often happens due to a lack of vitamin D particularly in adults. It can also occur if the body does not get or absorb enough calcium and other nutrients needed to keep bones strong.

What is osteoporosis?

Osteoporosis is a condition where bones become thin, weak, and more likely to break. It is often caused by low levels of vitamin D and calcium. Other risk factors may include family history, low body weight, lack of exercise, smoking, drinking too much alcohol, or having certain health conditions like rheumatoid arthritis.

Is there any correlation between the nutrients vitamin D and calcium?

Yes, vitamin D helps your body absorb calcium. Without enough vitamin D, your body can only absorb a small amount (10 to 15 %) of dietary calcium. But when your vitamin D levels are optimal, your body can absorb a lot more calcium (30 to 40%), which helps keep your bones strong.

Content created by

Dr. Swati Gupta (Anand)

MD Lab Medicine, MBBS

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Last Updated

7th Oct 2025