A different personal experience. I had Vit D deficiency. Started on 2000IU per day and was still deficient after months. Then started on 5000IU per day, initially daily but now every other day or so. My last test was in the middle of the "normal" range. I have been taking VitD for 4 years or so. A lot of my symptoms like tiredness, sleepiness etc have improved since then.

I asked my immediate family members to do a test as well. Male/female, young old, across states and even countries. All of them except my mother had low Vit D levels. My mother regularly supplements as its recommended for bone loss prevention in that age.