Vitamin D

The basics

25-hydroxyvitamin D (25-OH-D) is the main storage form of vitamin D in your blood, and the standard marker for assessing vitamin D status. It is produced when ultraviolet B light converts a cholesterol precursor in your skin into vitamin D, which the liver then hydroxylates into 25-OH-D.

Why this marker matters

Your 25-OH-D level reflects the combined input from sun exposure, dietary intake, and supplementation. Low levels are common in Northern Europe, particularly in winter and in people who spend most of their time indoors. Adequate vitamin D matters for bone mineralisation, muscle function, and a number of immune-system processes.

Where the typical ranges sit

German reference (DGE): sufficient from 20 ng/mL (50 nmol/L); many labs and international guidance target 30 ng/mL.

The thresholds genuinely differ between Germany and the widely quoted US ones, so it is worth knowing which you are being measured against. The German reference (DGE, echoed by the RKI) treats a 25-OH-D level from 20 ng/mL (50 nmol/L) as sufficient for bone health, and below roughly 12 ng/mL (30 nmol/L) as deficient. The 2011 US Endocrine Society guideline set a higher bar - deficiency below 20 ng/mL, insufficiency 20–30, sufficiency 30–50 ng/mL (75–125 nmol/L) - and many laboratories still report against it, which is why a value in the low 20s can read as "sufficient" in Germany and "insufficient" on an American scale. The Endocrine Society itself stepped back from population-wide targets in its 2024 guideline. Values much above 100 ng/mL (250 nmol/L) can indicate over-supplementation and may warrant discussion.

Reference ranges differ between laboratories and guidelines. Your CHIRAYOU report uses the range reported by the analysing laboratory, and your interpretation should be discussed with a physician.

Common influencers

• Sun exposure (latitude, season, sunscreen, indoor lifestyle)
• Skin pigmentation (darker skin produces less vitamin D per UV unit)
• Body weight (vitamin D is fat-soluble and stored in adipose tissue)
• Dietary intake (fatty fish, fortified foods)
• Supplementation
• Conditions affecting fat absorption (e.g. coeliac, IBD)

If your value is outside the range

A low value is straightforward to address with supplementation in most cases, but the dose and duration should be discussed with a physician - particularly if you have kidney issues, are pregnant, or take medications that interact with vitamin D metabolism. Levels should be rechecked after a few months of supplementation.

Where this comes from

• Deutsche Gesellschaft für Ernährung (DGE) - Referenzwerte für Vitamin D (the German reference: 25-OH-D from 50 nmol/L is adequate)
• Robert Koch-Institut - Vitamin D
• Holick M. F. et al. - Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline (JCEM, 2011) - the source of the 30 ng/mL threshold
• Demay M. B. et al. - Vitamin D for the Prevention of Disease: an Endocrine Society Clinical Practice Guideline (JCEM, 2024)