The protein in the hair is Keratin. The body throws out this unwanted protein as near waste needed only for the nails and hair. The harder Keratin is in the nails. A lie repeatedly told, sounds like the Truth' is a Chinese proverb. This is proved by the blind faith many place on Shampoos, due to advertisements.
Shampoo is just a perfumed, cleaning agent for the hair.
The extra additives cannot help much. The Scalp is not a Second Stomach to digest Proteins, Vitamins, etc. If Shampoo holds the 'key', Americans and others should have had some control on hairloss and dandruff at least 50 years back. It was formulated long back and many reputed Pharmaceutical, Consumer Products and Cosmetic Companies make them. Some of the brands are world famous.