Vitamin D: who actually benefits, and who's wasting money
the evidence, graded
- Claim
- Everyone should supplement vitamin D.
- What the evidence says
- Strong for correcting genuine deficiency, especially over winter and in people who get little sun. For already-replete adults, large trials show little benefit on most hard outcomes.
- Bottom line
- If you're deficient or rarely see the sun, a modest daily dose is sensible. If your level is already fine, more isn't better.
Vitamin D is the rare supplement where the official advice and the hype almost agree — but not for the reason most people think.
The strong part
If you’re genuinely deficient, correcting that matters — for bone health especially. People with little sun exposure, darker skin, or who cover up are most likely to be low, and a modest daily dose reliably fixes it.2
The weak part
The leap from “fixes deficiency” to “everyone should megadose for their heart, mood, and immunity” isn’t supported. The largest trial of healthy, mostly-replete adults found little effect on the big outcomes.1
Bottom line
Test or top up if you’re likely low. If your level is already fine, spending more on higher doses is buying very little.
references
No industry funding · sources linked above · flagged where the evidence is weak.
Get the next one in your inbox
One graded breakdown a week — health, AI, or building. Five minutes, sourced.