Vitamin B12 helps produce oxygen-rich red blood cells, which carry oxygen to your hair follicles. These are the hair cells within your body that are responsible for growth. If you have a vitamin B12 deficiency, these cells will struggle to replicate and your hair growth may be stunted. B-Complex vitamins help to promote healthy hair growth by ensuring that new cells are produced at a steady rate. Vitamin B12 is essential for women of childbearing age because it decreases the likelihood of birth defects in the unborn baby.