Yes, they did a study comparing vitamin d to placebo, but they only gave the study kids 1200 iu! Imagine how much better the results would have been if they gave them 4000 iu. (The placebo kids did have double the cases as it was, but I would bet very few would even catch the flu with a therapeutic dose.
Here is how I figured dosing a child of average size (for this purpose, call average size wearing the size clothing that matches his age). From birth, one drop on mom’s or bottle nipple of 400 iu a day. Double if ill. From 2, 1000 iu a day, double if acutely ill. From 4, 2000 iu a day. From 6, 4000 iu a day until puberty, then 5000 iu a day or get tested until your blood registers at least 50. Adults should be tested. I need 10,000 iu a day.
We don’t get sick and we do get exposed to all kids of flus and colds.
We homeschool and live below 35N. Recess is every day at 11:30 for ~20 min. Just like when I was in school in the stone age. Unless it’s below 40, over 100 or raining. Haven’t had the kids D tested though. We’re part NA so they’re darkish to begin with. Our ENT suggested the D3 in olive oil drops if you can believe it. We do 500iu/day for the kids and 5000iu/day for the adults. I have had my levels tested and the sun wasn’t doing the job (tan skin) so I had to add the supps.
I do agree they should have had a couple more study dosages at least. There might be a plateau effect somewhere.