Vitamin D vs B12 - what's the difference?
Both are commonly deficient, but they do different jobs: vitamin D is for bones and immunity, B12 for blood and nerves. Here's the breakdown.
Vitamin D
Affects calcium absorption, bones and immunity. Made in the skin from sunlight; deficiency is very common.
Vitamin B12
Needed for blood production and the nervous system. Comes from animal foods; deficiency is common in vegans and older adults.
Vitamin D vs Vitamin B12
| Vitamin D (25-OH) | Vitamin B12 (Cobalamin) | |
|---|---|---|
| Unit | ng/mL | pg/mL |
| Typical adult range | 30–100 ng/mL | 200–900 pg/mL |
| Common reasons for a high value | Over-supplementation; Granulomatous diseases | Recent supplementation or B12 injections; Liver disease |
| Common reasons for a low value | Limited sun exposure; Malabsorption | Vegan / strict vegetarian diet; Pernicious anaemia |
Key differences
- Vitamin D is bones/immunity; B12 is blood/nerves.
- D depends on sunlight; B12 on diet (animal foods).
- B12 deficiency can cause anemia and neurological signs; D - fatigue, bone issues.
- They're different tests; often checked together in a vitamin panel.
Bottom line
Different vitamins, different roles - not interchangeable. For fatigue or a restricted diet, your doctor may check both.
Frequently asked questions
Can I check both at once?
Yes - they're often in the same vitamin panel, along with folate.
Which is more commonly deficient?
Vitamin D is very common (little sun); B12 especially in vegans and older adults.
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