There are numerous nutrients that have been shown to prevent hair loss and help grow hair.  Hair loss can be caused by many things, such as aging, drug use, infections as well as vitamin deficiency.  By adding vitamins to the diet, you can help hair grow by improving circulation, adjusting hormones and reducing stress, all of which are causes of hair loss.

Vitamin A regulates synthesis of retinoic acid in the hair follicle, and it can be applied to scalp and massaged in as well as taken internally.
Vitamins B can help reduce stress which causes hair loss.  Inositol (one of the B Vitamins) has been known to speed up hair growth.  B12 helps prevent hairloss as it is a component of the hair itself.  B12 is usually found in meat and eggs, so many vegetarians are B12 defecient.

Vitamin C helps body absorb iron which is needed for hair growth.  The body does not create its own vitamin C so vitamin C rich foods or supplements are recommended.  The daily dose of vitamin C is between 1000 to 2000 mg per day.

Taking Vitamin D stops hair loss.  A 2009 research reports that Vitamin D reduces hair loss by stimulating the hair follicle and the cells that form the hair shaft.  Due to a research that shows a world wide Vitamin D deficiency, the recommended daily intake has been changed from 400 to a minimum of 1000 IU daily.

Vitamin E stimulates hair follicles that grow hair by building caipllaries and improving blood flow and can be massaged directly into scalp to encourage blood flow to the scalp.