D vitamin low after three years of suplement

[Rogolavet]

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.

[Red_Star]

Optimal vitamin D for calcium absorption is 79.8 nmol/L. For overall health optimal vitamin D is 100 to 150 nmol/L. Vitamin D is fat soluble so take with meals containing fat. Make sure you have enough magnesium which is the most important co factor for vitamin D absorption.
Inflammation affects vitamin D absorption.

[Annafill]

I think it's best to consult a doctor. There is also vitamin D at a dosage of 4000 IU, you can drink it for at least 3 months, and then do an analysis and check the results.