Vitamin D

Vitamin D is a fat-soluble vitamin that your body can produce when your skin is exposed to sunlight. It helps your body absorb calcium, which is essential for strong bones. Vitamin D also plays a role in immune function, muscle function, and cell growth. The 25-OH Vitamin D test is the most accurate way to measure how much vitamin D is in your body.

Vitamin D is tested to check for deficiency or insufficiency, to monitor supplementation, and to evaluate bone health. It's particularly common in people with limited sun exposure, darker skin, or certain medical conditions.

Vitamin D is measured with a simple blood test. The most common test measures 25-hydroxyvitamin D [25(OH)D], which reflects both dietary intake and sun-produced vitamin D. No fasting is required.

A common reference range for 25-OH Vitamin D is 30-100 ng/mL for sufficient, 20-29 ng/mL for insufficient, and below 20 ng/mL for deficient. However, reference ranges can vary between laboratories and professional guidelines. Some organizations use different thresholds. Always discuss your results with your healthcare provider.

• Sun exposure
• Skin pigmentation
• Age
• Diet and supplementation
• Season and latitude
• Body fat percentage
• Certain medical conditions

Frequently asked questions

• · Endocrine Society. Evaluation, Treatment, and Prevention of Vitamin D Deficiency.
• · National Institutes of Health. Vitamin D Fact Sheet.