The body produces the keratin it needs from proteins in its diet. In addition, vitamins such as biotin and vitamin A are also involved in keratin production. If the body cannot produce enough keratin (e.g. because the diet is too low in protein or important nutrients), it will show in the hair, nails and skin. Hair and nails may grow more slowly and become more brittle, duller and less shiny. Another effect may be thinner hair. The skin may appear duller, drier and even ageing.