People also need to take a much higher dose than the recommended 400 IU. During Covid I took 30,000 IU for something approaching a year. During that period, I never got sick. My blood levels got up to 150 ng/ml which most doctors consider an overdose, but the proven overdose blood level is actually 300 ng/ml, (I suspect that it is even higher when taking K2) but the guy that did the testing arbitrarily suggested staying below 100 ng/ml. Then doctors, thinking 100 ng/ml was an overdose, recommended 40 ng/ml, which is way too low. I lowered my doses to only 10,000 IU and dropped to 80 ng/ml and started fighting colds again. I'm going to up my intake again.