Question: what is the best supplement to promote hair growth?
Answer: Vitamin A. All cells need vitamin A for growth. ... 
B-Vitamins. One of the best known vitamins for hair growth is a B-vitamin called biotin. ... 
Vitamin C. Free radical damage can block growth and cause your hair to age. ... 
Vitamin D. ... 
Vitamin E. ... 
Iron. ... 
Zinc. ... 
Protein.