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Vitamins & Minerals

Vitamin D (25-OH Vitamin D)

The 25-hydroxyvitamin D test — the standard blood test for vitamin D status — measures the total circulating form of vitamin D in your body. Vitamin D is unique: your skin manufactures it when exposed to UVB sunlight, and it functions more like a hormone than a traditional vitamin, influencing over 1,000 genes involved in immunity, bone health, muscle function, and mood.

Normal Range

Sufficient: 30–100 ng/mL; Insufficient: 20–29 ng/mL; Deficient: <20 ng/mL

Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.

Why is Vitamin D measured?

Vitamin D deficiency is among the most prevalent nutritional deficiencies worldwide, affecting an estimated 1 billion people. Testing is recommended for people at risk — those with limited sun exposure, dark skin, obesity, malabsorption conditions, or unexplained bone pain, fatigue, or muscle weakness.

High Vitamin D means…

Vitamin D levels above 100 ng/mL are considered potentially toxic. Vitamin D toxicity (hypervitaminosis D) is almost always caused by excessive supplementation — not sun exposure. It causes calcium to build up in the blood (hypercalcaemia), leading to nausea, kidney stones, and in severe cases, heart rhythm problems.

Low Vitamin D means…

Below 20 ng/mL is deficient. Deficiency impairs calcium absorption, weakening bones (leading to osteoporosis and osteomalacia). It is also associated with increased risk of infections, autoimmune conditions, depression, and some cancers — though causality for non-bone outcomes is still being researched.

Symptoms associated with abnormal Vitamin D

When Vitamin D is high:

  • Nausea, vomiting, and loss of appetite
  • Excessive thirst and frequent urination
  • Kidney stones or kidney damage
  • Muscle weakness and confusion

When Vitamin D is low:

  • Bone pain and muscle aches
  • Fatigue and low energy
  • Frequent infections or prolonged illness
  • Low mood or depression
  • Hair loss in severe deficiency

How to improve your Vitamin D

  • 10–20 minutes of midday sun on arms and face (without sunscreen) several times per week significantly raises vitamin D in most people.
  • Fatty fish (salmon, mackerel, sardines), egg yolks, and fortified milk are the best dietary sources.
  • Most adults with deficiency need 1,500–2,000 IU/day of vitamin D3 to reach sufficient levels; obese individuals may need 2–3× more.
  • Take vitamin D with a meal containing fat — it's fat-soluble and is absorbed much better with dietary fat.
  • Retest after 3 months of supplementation to confirm your levels have normalised.

Frequently asked questions about Vitamin D

What is a normal vitamin D level?

Most guidelines define sufficient vitamin D as 30–100 ng/mL (75–250 nmol/L). Levels of 20–29 ng/mL are insufficient, and below 20 ng/mL is deficient. The Endocrine Society considers levels above 40 ng/mL optimal for most health benefits.

Can I get enough vitamin D from diet alone?

Very few foods are naturally rich in vitamin D. It is extremely difficult to reach sufficient levels through diet alone — sunlight or supplementation is necessary for most people, particularly those living above 35°N latitude from October to March.

How long does it take to correct a vitamin D deficiency?

With appropriate supplementation (typically 2,000–4,000 IU/day), most people see their vitamin D levels normalise within 3 months. Severely deficient patients may require short-term high-dose loading (50,000 IU weekly) under medical supervision.

Is vitamin D deficiency linked to depression?

Observational studies show a consistent association between low vitamin D and higher rates of depression. However, large clinical trials of vitamin D supplementation have shown mixed results for improving mood. It is plausible that deficiency contributes to depression risk, but supplementation alone is not a depression treatment.

Medical Sources

This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.