PORTLAND, Maine (NEWS CENTER) -- The endless quest to look our best has made beauty-focused vitamins a booming industry despite little evidence of their effectiveness.

In vitamins that advertise longer hair, healthy skin and stronger nails, the key ingredient is often biotin. It's a water-soluble vitamin humans need to maintain healthy cell growth which does include hair, skin and nails.

But registered and state-licensed dietician Grace Violette says the 30 to 75 micrograms of biotin the average American consumes as part of a regular daily diet is already perfectly adequate.

Other than biotin, beauty-focused vitamins often contain little to none of other beneficial minerals that can typically be found in traditional multivitamins

A vitamin supplement can contain anywhere from 1,000 to 5,000 micrograms of biotin. But unless you have a biotin deficiency, Violette says you probably won't absorb much more than your body already gets from food. Additionally, these beauty-branded vitamins often contain little to none of the other minerals like iron, calcium and zinc found in traditional multivitamins.

There is no concrete scientific evidence supporting claims that taking biotin supplements impacts the health of hair, skin and nails. As stated on the vitamin's labeling, the U.S. Food and Drug Administration doesn't evaluate such claims, nor does it review the effectiveness of any dietary supplement.

The label on bottles of biotin vitamins includes an advisory which states that the U.S. Food and Drug Administration does not evaluate the effectiveness of dietary supplements

Consulting with a doctor is a good idea before beginning a vitamin regimen. Violette says a varied diet is the best option to get more minerals and vitamins in your system naturally.