Vitamin D (25-OH)
Vitamin D is a hormone produced in the skin under the influence of sunlight (and some from food). It regulates calcium and bone health and supports immunity and muscles. The 25-OH-D form is measured, as it best reflects your stores.
| Rating | Range | What it means |
|---|---|---|
| Talk to a doctor | below 30 nmol/L | Deficiency (<30 nmol/L) — supplementation is warranted. |
| Worth improving | 30 – 50 nmol/L | Insufficiency (30–50) — maintain your stores (sun/D3 in winter). |
| Good | 50 nmol/L and above | Adequate (≥50, WHO/IOM consensus). ES 2011 proposed ≥75 (withdrawn 2024 — under debate). |
Why it matters
Endocrine Society/ESCEO: deficiency is common and affects bones and immunity.
If it’s low
Low vitamin D means impaired calcium absorption and poorer support for bones, immunity and muscles. Often without obvious symptoms, but worth correcting — cheap and safe.
If it’s high
High vitamin D is almost always the result of excessive supplements; sunlight does not produce too much. Very high levels can raise calcium — so do not overdo supplements.
What to do
Low in winter is common — a safe D3 supplement (after consultation) and some sun in the warmer half of the year. Also check calcium and PTH if it is markedly low.
Read together with
Calcium · Parathyroid hormone (PTH) · Phosphate
Part of the guide: Vitamins & minerals →
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This content is for information only and is not a substitute for medical advice. Talk to your doctor about your results.
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