I’ve been taking between 5000 and 10,000 units daily since Jan 2020. Still getting at least one bad cold annually.
If I were to get a cold or flu I would take 900 units per pound of body weight all at one time. It is a flu and cold killer and fixes it for me and my relatives and friends in about 8 hours. I was told by my MIL who first introduced me to D3 19 years ago that if that doesn’t do it repeat once. I don’t know anyone who has had to repeat.