>Bolus vitamin D3 supplementation during or just before COVID-19 was associated with better survival rate in frail elderly.
That's rather close to the headline.
No.
The HN headline implies causation. The study result does not. (The study authors try to imply causation as well, but that's not what the study says.)
Agreed. To support what you said: the phrase "was associated with" is not a causative claim. You cannot go from that phrase to "improves."