YES, vitamin D…… but you must test…..otherwise you guess. Your blood (serum) level needs to get up toward 100 ng/ml to be therapeutic. I ask everyone, “what is your number?” Almost no one knows. I usually get exactly what you said
That is not an answer. Here is why: an individual taking 4000 IU per day could range from 10 ng/ml up to 150 ng/ml. That is from statistics including 7300 people over 18. We are all different. For example, I take around 12,000 IU per day (with food, very important) and my number stays between 85 and 110.