Vitamin D (25-OH): what it means.

Drives immune function, mood, bone health, and calcium handling.

Written to our editorial standards · reviewed against published research· Updated 27 Jun 2026
Typical reference bands (ng/mL)
Lowunder 20 ng/mL
Borderline low20-30 ng/mL
Optimal40-80 ng/mL
Highover 100 ng/mL
Ranges vary by laboratory, age, and sex, your lab's own reference range always takes precedence.
What does low vitamin d (25-oh) mean?Causes, symptoms & what to do →

Common causes

  • Limited sun exposure, especially in winter or at northern latitudes
  • Darker skin, which needs more sun to make vitamin D
  • Older age and less efficient skin synthesis
  • Higher body fat, which sequesters vitamin D
  • Malabsorption (celiac, Crohn's, gastric surgery)

What it can feel like

  • Fatigue and low mood
  • Frequent infections
  • Bone aches or muscle weakness
  • Hair thinning

Who should test

Worth testing if you get little sun, have darker skin, feel persistently run down, or have a bone-health concern. Many clinicians retest 8 to 12 weeks after starting a supplement.

Supplements that help raise Vitamin D (25-OH)

Evidence-led, and only a piece of the picture, diet, lifestyle, and your clinician matter most.

Vitamin D3 raises blood 25-OH-D more reliably than D2, and pairing it with vitamin K2 helps direct the resulting calcium into bone rather than soft tissue.

Shop the top pick for vitamin d (25-oh)
NOW Foods Vitamin D-3 & K-2
Recommended
NOW Foods, Vitamin D-3 & K-2
120 veg capsules · ~$12 · ★ 4.8

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Vitamin D3 + K2Energy · bone · immuneStrong

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Common questions

What does a low Vitamin D (25-OH) mean?
Common drivers include limited sun exposure, especially in winter or at northern latitudes; darker skin, which needs more sun to make vitamin D; older age and less efficient skin synthesis. A result outside the optimal range is best read in context: discuss it with your clinician, who can weigh the full picture and your lab's own reference range.
What supplements help raise Vitamin D (25-OH)?
Evidence-led options include Vitamin D3 + K2. They support, but don't replace, diet, lifestyle, and medical care.

Educational use only, not medical advice or diagnosis. Always interpret lab results with a qualified clinician.