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Blood testDeeper health assessmentSituational

Vitamin D

Shows whether you have enough vitamin D for strong bones, muscles and immune health.
TypeBlood test
HowStandard blood draw or finger-prick kit.
How oftenOnce if at risk; 3 months after changing your dose.
BeforeNo preparation needed.
WhoPeople with little sun, darker skin, 60+, bone concerns or absorption problems.

Why vitamin D is worth knowing

Your skin makes vitamin D from sunlight, and it helps you absorb calcium and keep muscles strong. Many people run low - especially in winter - without noticing.
Who runs low
“Am I likely to be low?”
Little sun, darker skin, indoor work, 60+, higher body weight or gut conditions.
Common
What it does
“Why does it matter?”
Bones, muscle strength, falls and immune function.
Bones & muscle
Balance
“Can I take too much?”
Yes - very high doses can raise calcium. Test, then supplement to a target.
Test first

Is it right for you?

Worth considering if…

  • You get little sun or have darker skin.
  • You’re 60+ or have low bone density.
  • You have a gut condition that affects absorption.
  • You’ve started supplements and want to check your dose.

A better option if…

  • You’re healthy and already take a standard dose - routine screening isn’t recommended for everyone.

How it’s measured

Lab blood draw
Ask for 25-hydroxy vitamin D - the standard test.
Finger-prick kit
Convenient at-home option through certified labs.

The full picture

What is it?
The main circulating form of vitamin D (25-OH D).
What type of test is it?
A blood biomarker.
What does it measure?
25-hydroxy vitamin D in ng/mL or nmol/L.
Why might someone consider it?
Low levels affect bones and muscles and are common.
Who is it most relevant for?
People with risk factors for deficiency.
How is it performed?
A blood draw or finger prick.
How often might it be considered?
Once if at risk; 3 months after changing supplements.
What can the result help you understand?
Whether you need more, less or no supplement.
What are its limitations?
Screening everyone isn’t recommended; levels change with seasons.
What should it be viewed with?
Calcium, bone density, PTH, sun exposure and diet.

Where to get it

Through your provider
The simplest route - often covered when there’s a clear reason.
Lab services
e.g. Quest Diagnostics, Labcorp.
Direct-to-consumer panels
e.g. Function Health, InsideTracker.
Names are examples only, not endorsements. Your provider can often order the same test - and help interpret it.

Connected to

DEXA bone density →Ferritin + iron studies →Magnesium →Bone health guide →Vitamins & minerals guide →

Questions to ask your provider

  1. Am I at risk of low vitamin D?
  2. What dose should I take and for how long?
  3. When should I retest?
Ziva Health

One test is a snapshot. Ziva shows the whole story.

Ziva brings your lab results, wearables and daily readings together - and Isabella tells you what’s changing and what to ask your provider next.
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Is your provider not on Ziva yet? Send them a link in under a minute - once they join, they’ll see your Vitamin D result alongside your other trends and get alerts directly.
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Already seeing your provider?
Bring your Ziva 30-day report to your next appointment - your Vitamin D result and daily trends in one view, so the conversation starts with the full picture.
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Being listed doesn’t mean everyone needs this test. Educational only — not medical advice. Results should be interpreted with a qualified clinician. ← Back to Know What to Test