Products labeled "hair loss vitamin supplements" are easy to find, but finding ones that actually make a difference can be more of a challenge. Vitamins play a role in cellular health and regeneration, and all bodily functions. A balanced diet that is rich in vegetables, protein, fruits, and healthy fats is ideal, but if you're not sure you are getting all the nutrition you need from food sources, then supplementation may be a good idea. Boosting certain vitamin levels will ensure that your hair follicles are getting what they need to work optimally.
Among ingredients in hair loss prevention vitamins brewer's yeast is mentioned frequently. It is rich in B vitamins and trace minerals such as copper, zinc, and selenium, all of which are good for your hair. Genuine brewer's yeast has chromium as well, while nutritional brewer's yeast (the kind you find in health food stores) does not. Scientist suspect that brewer's yeast may have as-yet-unidentified nutritional components that are beneficial. Fortunately, brewer's yeast is easily digested, and the nutrients from it are readily assimilated into the body. You can get brewer's yeast in tablets and in powdered form that can be mixed in with juice.
If you've read at all about hair loss prevention vitamins pantothenic acid has no doubt come up. Also known as vitamin B5, pantothenic acid is one of the valuable B vitamins that are so important to healthy hair growth. Other B vitamins that are good for the hair are B6, biotin, folic acid, inositol, and niacin. 
Hair loss vitamin supplements often contain B vitamins, plus zinc, sulfur, and magnesium. Some supplements contain essential amino acids that have been found to affect hair in laboratory animals. In one study, rats fed a diet deficient in magnesium lost hair in clumps, and similar problems were noted with other B vitamin deficiencies. Biotin and inositol deficiencies also caused hair loss, but it was found to be reversible. Extremely large doses of vitamin A over a long period of time can trigger hair loss, but this is reversible.
Essential fatty acids found in primrose oil, fish oil, and flaxseed oil have been shown to improve the texture of hair and help keep it from getting dry and brittle. Coenzyme Q10, L-cysteine and L-methionine are said to improve the texture and quality of hair. The overarching concept is that poor nutrition is bad for hair, and good nutrition is good for hair. If you're not sure that you eat as well as you should, then vitamin supplementation - as long as it doesn't involve extreme dosages - may be a good idea for ensuring that your hair follicles have all the nutrients they need to work properly.