Headline is imprecise. The study is saying that higher doses of vit D do not strengthen bone more than lower doses, not that they don't strengthen bone at all, which is suggested by this headline.
> At trial end[...]
> mean percent change in [radial] volumetric BMD of −1.2% (400 IU group), −2.4% (4000 IU group), and −3.5% (10 000 IU group).
> mean percent change [...in tibial volumetric BMD] of −0.4% (400 IU), −1.0% (4000 IU), and −1.7% (10 000 IU).
> There were no significant differences for changes in failure load (radius, P = .06; tibia, P = .12).
The bone density decreases may look minor on paper but look at it this way: it’s quite possible that a very large cohort of elderly and middle aged people concerned about their bone health (potentially because they were told they have reason to be concerned) have been paying a lot of money annually to actually worsen their situation. That sucks.
One of the findings (there's a summary somewhere): https://epic.iarc.fr/highlights/vitamindcolorectal.php
>Main Outcomes and Measures: Co-primary outcomes were total volumetric BMD at radius and tibia, assessed with high resolution peripheral quantitative computed tomography, and bone strength (failure load) at radius and tibia estimated by finite element analysis.
>Conclusions and Relevance: Among healthy adults, treatment with vitamin D for 3 years at a dose of 4000 IU per day or 10 000 IU per day, compared with 400 IU per day, resulted in statistically significant lower radial BMD; tibial BMD was significantly lower only with the 10 000 IU per day dose. There were no significant differences in bone strength at either the radius or tibia. These findings do not support a benefit of high-dose vitamin D supplementation for bone health; further research would be needed to determine whether it is harmful.
Headline is not imprecise according to above-cited Conclusions and Relevance.
No, aladoc99 is right, because the study doesn't compare against 0. So you don't know if 4000 and 10000 improve strength compared to 0, only that they don't compared to 400. It's not a hill that someone should die on, though.
And thus we have ourselves a quandary, but truth isn't diminished by the practical limits of safe experimentation. We don't have to lie just because.
> it would be harmful to the subjects.
That doesn't make the title precise or the observation inapt.