> I think the headline is accurate. The 52% number is from the experiment arm (participants who received a vitamin D supplement, with the quantity guided by blood testing). While it’s technically possible for the supplement dosage to be calculated as zero, 85% of participants were deficient at baseline, so this isn’t the main effect.

Yes, but it's also important to note that the study wasn't on a representative sample of the general population. They recruited people who had acute coronary syndrome. The average age was over 60 years old, 80% were men, and half of them had already had at least one heart attack.

I think the supplements are just average Vitamin D off the grocery store shelf. Malabsorbtion is obvious possible.