Read up on the three best supplements for hair health and how to determine which is right for you.
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Hair Health Hotline: What are the most important vitamins for hair growth, and how can I know if I'm getting enough?
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Hair Health Hotline is your direct access to dermatologists, trichologists, hairstylists, and other beauty pros. Each story in this series tackles a common hair or scalp concern and offers science-backed solutions to care for your strands.

Many people swear by an "inside out" approach to beauty, focusing not just on the creams they're slathering on but what they're consuming as well. As the logic goes, getting the proper balance of nutrients and the right amounts of them will keep all of your body's various systems (from digestion to metabolism, and immunity) functioning properly, all of which will be reflected in the health and appearance of your hair, skin, and nails.

If you've ever comparison shopped the countless supplements on the market, though, you know that the list of nutrients that reportedly play a role in hair growth is long — and daunting. To help you cut through the noise, Elizabeth Boham, M.D., M.S., R.D., functional medicine physician and medical director of the UltraWellness Center, is breaking down the most helpful supplements for hair growth.

Q: My hair isn't as thick and full as it once was. Is there a supplement for hair growth that can help?

A: If you experience hair thinning because your diet is lacking in a specific nutrient, addressing your deficiency through supplements may help restore healthy growth. However, you want to avoid just choosing any random daily multi-vitamin on the shelf, as a more targetted approach may be best, according to pros. Before diving in, be sure to consult your healthcare provider for the necessary bloodwork or other testing needed to determine the best hair growth supplement for you.

How Supplements Can Impact Hair Growth

If you're experiencing hair loss or hair thinning, your diet may be fully or partially to blame. "So often there are multiple things coming together that are influencing someone's health and hair growth," says Dr. Boham. That said, nutrition is a common factor, she says. "When people come to [my colleagues and I] complaining of hair loss and we do testing, so often we find issues with nutritional status," says Dr. Boham. "I would say at least half the time I see issues with nutrition that are contributing to hair loss." And that's where supplements come in.

Hair Health Hotline: What are the most important vitamins for hair growth, and how can I know if I'm getting enough?
Credit: Courtesy of Elizabeth W. Boham

Best Supplements for Hair Growth and Thickness

Iron, protein, and biotin are three of the nutrients that most commonly impact hair growth, according to Dr. Boham. These three nutrients can have an effect on the number of strands sprouting from your scalp, the thickness of your strands, or both. "Especially with biotin and amino acids, a deficiency impacts the thickness of the hair, the brittleness of the hair, the quality of the hair," she says. "Iron and amino acids tend to impact the volume of the hair, the amount of hair."

Iron

First up, an important mineral that your body needs to make certain proteins and hormones. "Iron is the nutrient that most commonly affects hair growth and causes the most significant shift," says Dr. Boham. While experts don't fully understand the role that iron plays in hair health, one theory is that when your body is low on iron, it diverts iron stored in your hair follicles elsewhere, leaving hair weaker.

People who menstruate — and especially those with a heavy flow — often have low iron levels, and some people just don't absorb iron well, says Dr. Boham. Additionally, if you're on a vegetarian or vegan diet, it's more difficult (though not impossible) to maintain adequate iron levels, since the iron in plants such as beans, legumes, and spinach, isn't as easily absorbed by your body as the form of iron in animal proteins.

Protein

Protein doesn't just play a role in post-workout recovery, it also provides structure to your hair. Both protein and amino acids (the building blocks of protein) can be helpful hair growth supplements for those who aren't getting enough protein, says Dr. Boham.

"Protein deficiency is more common in people who are restricting their diet for some reason, are vegetarians or vegans, are older and are just eating fewer calories, or have digestive issues such as SIBO (small intestinal bacterial overgrowth)," says Dr. Boham. When hair loss is present for this reason, "I often give amino acid supplementation to help hair regrow, and it works really well," she says.

Biotin

If you've ever investigated "hair, skin, and nail" supplements, then you saw this suggestion coming. Biotin, aka vitamin B7, is important for maintaining metabolic health, nervous system functions, and strong hair, skin, and nails. "It's known that biotin affects the quality of hair," says Dr. Boham. "People who are low in biotin will have rougher hair, brittle hair, hair breakage."

However, biotin deficiencies are less common than the marketing campaigns for supplementation may lead you to believe. "Biotin is not as common of a deficiency as iron or the amino acids," says Dr. Boham. Anecdotally some people have reported improved hair growth from taking biotin in the absence of a deficiency, but biotin doesn't necessarily benefit those who aren't lacking in the vitamin, she explains.

How to Choose a Hair Growth Supplement

Ideally, you'll get enough of these and other nutrients your body needs through food, eliminating the need for hair growth supplements, says Dr. Boham. "Diet is always best," since you're less likely to run into toxicity (taking in too much of any given nutrient) that way, she says. "But if you're working with [a healthcare provider] who can test your levels and know exactly what you need, supplementation can really be effective when diet alone doesn't work," she says. Know that "it's really good to have a targeted approach to supplementation so you know what you're taking and for what reason." Consider visiting a nutritionist or medical professional who "can do an evaluation of your diet and nutritional status because that can help you know exactly what to take," and how much, says Dr. Boham. (Related: The Best Foods for Hair Growth, According to Dietitians)

That said, it's generally safe to add more protein to your diet if you take stock of your eating habits and realize you're failing to meet the daily recommended amount. Generally, one gram of protein per day per kilogram of your bodyweight suffices, says Dr. Boham. (Learn more about how to determine the right amount of protein every day for you, here.) "There are lots of different protein supplements out there from collagen to pea protein and people will notice a difference," she says. "And the amino acid supplements are the breakdown products of the protein. If it's a blend of amino acids most people tolerate it pretty well." (Related: What Eating the Right Amount of Protein Per Day Actually Looks Like)

With iron, though, you don't want to take matters into your own hands, says Dr. Boham. It's crucial to have your iron levels checked through bloodwork to find out where you stand since excess iron can cause organ damage.

Biotin is generally considered safe to take since consuming high amounts of biotin isn't known to be toxic. If you decide to try taking it as a hair growth supplement, you should be aware that it can impact other bloodwork results. "When you're taking high-dose biotin — 3,000 or 8,000 micrograms a day — that will impact some of your lab values, especially your thyroid levels," says Dr. Boham. "So, if you are taking biotin and you're having your thyroid checked because of hair loss, for example, you need to stop taking it five days before you have the bloodwork done" in order to have a "clean slate" for testing.

Selecting a hair growth supplement with a mix or combination of ingredients may not be as helpful as a more targeted approach, according to Dr. Boham, so you may want to choose against a daily multi-vitamin if hair regrowth or health is your specific goal.

When it comes to hair growth (and just overall health), iron, protein, and biotin are your friends. If you're failing to get enough of one of them through your diet, supplements may play a key role in your hair regrowth plan.

Have a hair health question you want answered? Send your Q to hairhotline@shape.com for a chance to have it featured in a future installment of Hair Health Hotline.