What this marker measures
Many labs use different cut-offs for "normal" vitamin D. Most guidelines consider 30 ng/mL (75 nmol/L) or above as sufficient. Vitamin D is made in skin with UVB sun exposure and is also obtained from certain foods and supplements.
High or low: what it can mean
High Vitamin D
Very high vitamin D (above 100 ng/mL) can cause vitamin D toxicity, leading to excess calcium absorption and symptoms such as nausea, weakness, or kidney stones. This is almost always the result of over-supplementation rather than sun exposure.
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Low Vitamin D
Low vitamin D is very common globally, especially in higher latitudes, in people who spend little time outdoors, and in those with darker skin tones. Deficiency may contribute to reduced bone density, immune function, and muscle strength.
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Lifestyle considerations
- •Safe sun exposure (10–30 minutes midday) stimulates vitamin D production
- •Fatty fish, egg yolks, and fortified foods provide dietary vitamin D
- •Supplementation is often needed in winter months at higher latitudes
Frequently asked questions
What is Vitamin D?
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The 25-hydroxyvitamin D test measures the storage form of vitamin D in the blood — the best indicator of overall vitamin D status. Vitamin D is essential for calcium absorption, bone health, immune function, and muscle strength.
What does Vitamin D measure?
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Many labs use different cut-offs for "normal" vitamin D. Most guidelines consider 30 ng/mL (75 nmol/L) or above as sufficient. Vitamin D is made in skin with UVB sun exposure and is also obtained from certain foods and supplements.
What does high Vitamin D mean?
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Very high vitamin D (above 100 ng/mL) can cause vitamin D toxicity, leading to excess calcium absorption and symptoms such as nausea, weakness, or kidney stones. This is almost always the result of over-supplementation rather than sun exposure.
What does low Vitamin D mean?
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Low vitamin D is very common globally, especially in higher latitudes, in people who spend little time outdoors, and in those with darker skin tones. Deficiency may contribute to reduced bone density, immune function, and muscle strength.
What supports healthy Vitamin D levels?
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Safe sun exposure (10–30 minutes midday) stimulates vitamin D production. Fatty fish, egg yolks, and fortified foods provide dietary vitamin D. Supplementation is often needed in winter months at higher latitudes
Related biomarkers
Editorial note
LabTestly explains lab markers using plain-English educational content. Reference ranges may vary by laboratory and should be interpreted with a clinician.
Educational content · Editorially reviewed for clarity · Last updated
Common sources used for lab-test education
Not medical advice
This page is for general understanding only and does not replace medical advice from your clinician. Reference ranges can vary by laboratory, age, sex, pregnancy status, medications, and clinical context.