I had been losing hair since I was 15, I have genetic history of hair loss (paternal side, except dad), And I was diagnosed with vitamin d3 deficiency when I was 18 years old. I have strong diffuse thinning, where hair is only a little thick at the lower back head. Hairline has receded only by a bit . I took action when I am 20 years now, recovered Vitamin D3 to 51 ng/l (from 9.5). But hair fall has not reduced or density has not come back. It's been 2 months since Vitamin d3 levels are normal.