Severe hairfall for past 2 years.

I have severe hairfall for past 2 years. I have been to general physician and dermatologist for this problem. They did blood test and told me that my vitamin D, iron value are very low. They put me on supplements for the same. Does vitamin D and iron deficiency cause hairloss? I have lost almost half of my hair in the past 2 years. My vitamin D is very low for past 2 years and I am taking 50000iu per week. My vitamin D value is 19.9 now. It was 12 last year. My results: Calcium - 9.4mg/dl reference - 8.7 - 10.2 TSH -  3.010uIU/ml reference - 0.450 -4.500uIU/ml Vitamin B12 - 406 pg/ml reference - 232-1245pg/ml Vitamin D -19.9  reference - 30-100ng/ml Iron - 37ug/DL reference - 27-159ug/DL  Iron Saturation - 9% reference - 15-55% Ferritin- 97ng/ml reference - 15-150ng/ml Free T4 - 1.36ng/DL reference - 0.82 -1.77ng/DL T3 Total - 159 ng/DL reference - 71-180 ng/Dl. What helps to reduce the hairfall?