So I checked my d vitamin level in 2019. and it was optimal but almost low. I started taking vitamin D suplement in the autumn of 2019., About 1000 IU per day, and even 2000 IU daily in past year. I checked my level yesterday again, three years of supplementation after, and it is 64.4nmol/L. Scale in the results says that optimal conc. is 75-250, insufficiency is 25-75 where I am, and deficiency is under 25, while toxic is over 250.
How is it possible that after years of daily intake I am still insufficient? I am confused.