Can 4 years of hair loss due to vitamin D deficiency be reversed once treated?

it matters how much hair you lost beacuse of the missing vitamin D. İf the ratio of the lost hair is on the high degrees, than even if you have a treatment the wole hair might not come back.

Hi, Vitamin D acts on the hair follicle to regulate gene expression to influence hair growth extending anagen phase and inhibiting catagen phase you can certainly take vitamin d to prevent further loss, you would need to get your blood drawn to see your level to determine how much vitamin d supplementation is needed typically 50,000 units once a week for 8 weeks then maintenance. Speak to your doctor first to see if you qualify. As if we could reverse hair loss only time will tell.

It is highly unlikely that Vitamin D intake at this point will restore your hair. However you should take a high quality supplement if you have a vitamin D deficiency.