The hair vitamin market is a booming industry. The effects of hair loss and thinning on self-image and self-esteem have been well documented, and with promises of thick, long locks, and hair restoration, it's no wonder many people are spending at least $176 million annually for these "miracle-in-a-bottle" supplement pills in a bid for healthy hair. However, there is no conclusive evidence these products actually work. So, are these pills just glorified placebos?

Most hair supplements contain more or less the same ingredients: Vitamin C, Biotin, Vitamin B3, and Vitamin A, all of which have been shown to be essential for hair growth. These elements are also essential for the body to function as efficiently as it can, and many of them can be found in a variety of foods and beverages.

"They’re not made-up pills. Our bodies are already taking them in and they should be a part of our diet," celebrity hair stylist Devin Toth, of Salon SCK in New York City, told Medical Daily. Toth has worked with celebrities like Pretty Little Liars star Shay Mitchell and fashion model Kate Upton. "Taking them as supplements consistently ensures that those nutrients and vitamins travel through our bloodstream to essential organs, then to our hair follicles and cortex."

Essential Vitamins Affect Your Hair

Considered one of the most effective nutrients to help grow and strengthen hair, vitamin C creates the collagen protein — an essential component of hair structure. It also helps the blood absorb iron, a mineral necessary for hair growth.

Biotin is a coenzyme that "reacts with enzymes to make amino acids, the building blocks of proteins such as keratin, the protein that hair is made out of," according to Toth. It is also associated with an improvement in the strength and elasticity of the cortex — the thickest layer of the hair, located between the hair cuticle and the medulla.

Vitamin B3, also known as Niacin, is used to treat high cholesterol and triglyceride levels, but it also keeps the blood flow to scalp high, bringing vitamin nutrients to the hair follicle and keeping the scalp hydrated.

Are these ingredients more effective than placebos when put into pill form? The answer is yes, according to a 2012 double-blinded study on the efficacy of Viviscal hair supplements. Viviscal researchers found the pill safely and effectively promoted significant hair growth in women with temporary thinning hair after 90 and 180 days.

Although the study was funded by Lifes2Good, the owner of Viviscal, researchers maintain the double-blind study design helped to avoid bias. They also noted their results may represent the first description of increased visible hair growth in women associated with the use of a nutritional supplement.

"I think there’s a lot of new evidence backing not just Viviscal but other supplements out there like Nutrafol," Dr. Ablon Glynis, dermatologist at Ablon Skin Institute and lead researcher of the 2012 study, told Medical Daily. "We're seeing more and more data, we’re seeing more and more in vitro studies where there are actually finding out what the supplement are doing as far as on the hair follicle."

"Reach Maximum Capacity"

Knowing that hair supplements are packed with growth-promoting vitamins is reassuring. However, the vitamin industry isn't strictly regulated by the U.S. Food and Drug Administration.

The FDA classifies vitamins as dietary supplements, and manufacturers are not required to obtain FDA approval before marketing. In other words, it’s not known whether the benefits of any of these dietary supplements outweigh the risks for intended use. What's more, there is a lack of data showing that these over-the-counter hair supplement products, including biotin supplements, actually work.

"While vitamin deficiencies — notably iron and vitamin D — can contribute to hair shedding, there just isn't data to support the efficacy of vitamin supplements, like biotin or Hairfinity. And people spend so much money on them," dermatologist Marie Leger told Medical Daily. Leger, who practices dermatology at NYU Langone Medical Center, said approximately 80 to 90 percent of her patients have tried biotin in a failed bid to restore hair loss before stepping into her office.

Leger isn't the only one to question this approach. Hair restoration surgeon Dr. Robert Leonard told Medical Daily earlier this month biotin supplements may be a wrong approach to hair loss. "Some people think that taking vitamins like biotin will help reverse their hair loss, but what they don’t realize is that hair loss is genetic, and you can’t really change your genetics," Leonard said.

Leger said an alternative to over-the-counter hair vitamins is the topical medication minoxidil, or Rogaine, which is backed by substantial evidence demonstrating its efficacy in boosting and regenerating the capacity for hair growth.

"It is thought to work by shortening the shedding portion of the hair cycle (telogen) and prolonging the growth phase (anogen) as well as converting miniaturized hair follicles that you can see with age-related, genetic hair loss (androgenetic alopecia) to thicker hairs," Leger added.

Toth thinks that, in addition to concern over lack of evidence, many people have reservations about hair supplement products because they have high expectations and get disappointed when they don’t see results right away.

"Vitamins and supplements aren't miracle drugs, they simply allow your hair to reach its full potential," Toth said noting that many hair supplements contain a vitamin rich compound. "[They] maximize what the body is capable of. Your hair needs certain things to reach maximum capacity … that’s what vitamins are for."

Vitamins works on hair from the inside — they have to travel through the bloodstream into the hair follicles. But since hair is a non-essential body part, said Toth, "it can take longer for it to receive the nourishment from the vitamins."