What do the states mean?+
- Solid: well studied, and it works.
- Half-there: the science is still forming.
- A ghost: almost no real studies.
- Hollow: well studied, and it does not work.
- A cord: the pair itself has been tested together.
- Air: nobody has ever tested this pair.
The full scoring method: How we score
Vitamin D benefits: where the science stands
For bone: no.
Bone is what most people take vitamin D for, and the strongest evidence says it does not help: a combined review covering 11 trials found no real difference. As of August 2026, the verdicts on this page rest on evidence from 17 trials, drawn from the strongest research among the 5,617 papers on PubMed that mention vitamin D. Every claim is checked below.
5,617 papers on PubMed · evidence from 17 trials
Claim by claim
- BoneWell studied, and it does not work. The biggest review covered 11 trials.
- Blood sugarWell studied, and it works. The biggest review covered 4 trials.
- PregnancyThe science is still forming. Results lean positive, but there is not much yet.
Pairs people ask about
The three sources we read
- 2019Meta-analysis · pools 11 trials, 34,243 people · no clear effect on bonesource
- 2024Randomized trial · 454 people · small benefit for pregnancysource
- 2025Meta-analysis · pools 4 trials, 5,205 people · small benefit for blood sugarsource
Chosen as the strongest evidence out of 5,617 papers on PubMed. Every row links to its paper.
Fair questions
Does vitamin D work?+
For bone, the strongest evidence says no. The biggest review covered 11 trials.
Is vitamin D safe?+
No caution is recorded on this page. That is not a safety guarantee; the studies we read were not safety trials.
Why only 3 sources, when PubMed lists 5,617?+
The 5,617 is every paper that mentions vitamin D in any way: animal studies, blood measurements, papers where it is a side note. The strongest sources are combined reviews, and each one already gathers every trial its authors could find. Our 3 cover 17 trials between them, and every one is linked above. Both counts are measured, not estimated.