Iron, Biotin, Zinc and Hair: What Matters and What's Hype

Walk down any pharmacy aisle and you will find shelves of hair supplements, often called "hair, skin and nails" formulas, with biotin front and center. For women noticing thinning hair in their 40s and 50s, they can feel like an easy first step.

The science tells a more nuanced story. Hair follicles are some of the most active cells in the body, so they do need a steady supply of nutrients. But taking extra nutrients when you are not deficient has little evidence of benefit, and some can cause problems. Here is a nutrient-by-nutrient look.

Protein: the building block

Hair is made mostly of a protein called keratin. When you do not eat enough protein, as can happen with very restrictive diets, the body may conserve protein by shifting hairs into the resting phase, which can lead to shedding.

Most women in the U.S. get enough protein, but needs and intakes vary, and getting enough becomes more important with age to protect muscle as well. Harvard's Nutrition Source recommends getting protein from a variety of foods, such as fish, poultry, beans, nuts, dairy and whole grains. See protein needs after 40.

Iron: the one most worth checking

Iron deficiency is the most common nutritional deficiency worldwide and is common among women who menstruate, particularly those with heavy periods, as often happens in perimenopause. Iron is needed to carry oxygen to cells, including hair follicles.

Low iron has been linked with hair shedding in some research, although the relationship is still debated. Dermatologists often check ferritin, a measure of iron stores, in women with hair shedding or thinning.

How much you need, according to the NIH Office of Dietary Supplements:

• Women 19 to 50: 18 mg a day
• Women 51 and older: 8 mg a day

Do not take iron supplements without testing. Too much iron can cause digestive problems and, at high levels, organ damage. The ODS sets an upper limit of 45 mg a day for adults unless a doctor advises otherwise. See our guide to iron, ferritin and energy.

Biotin: popular, rarely needed

Biotin, a B vitamin, is the star ingredient of many hair supplements. It is needed to turn food into energy, and severe biotin deficiency can cause hair thinning and a rash.

But here is the catch: according to the NIH Office of Dietary Supplements, biotin deficiency is very rare in people who eat a normal, varied diet. The adequate intake for adults is just 30 micrograms a day, and many hair supplements contain thousands of micrograms. There is little evidence that biotin supplements help hair in people who are not deficient.

The lab test problem

High doses of biotin can interfere with certain laboratory tests that use a biotin-based technology, causing falsely high or falsely low results. The FDA has warned that biotin can interfere with tests for troponin, a marker used to diagnose heart attacks, potentially leading to a missed diagnosis. Biotin can also affect thyroid test results.

If you take biotin, including in a multivitamin or hair supplement, tell your clinician before any blood test.

Zinc: important, but easy to overdo

Zinc is involved in cell growth and repair, immune function and wound healing. Zinc deficiency can cause hair loss, among other symptoms, though deficiency is uncommon in the U.S. Groups at higher risk include people with digestive disorders, vegetarians and people who drink heavily.

According to the Office of Dietary Supplements:

• Women need 8 mg of zinc a day.
• The upper limit for adults is 40 mg a day.
• Taking too much zinc over time can lower copper levels and affect immune function and cholesterol.

Good food sources include oysters, beef, crab, fortified cereals, beans, pumpkin seeds and dairy.

Vitamin D: an emerging area

Vitamin D receptors are found in hair follicles, and some studies have found lower vitamin D levels in people with certain types of hair loss. However, it is not clear whether low vitamin D causes hair loss or whether supplements help.

Vitamin D is important for bone health regardless. The Office of Dietary Supplements recommends 600 IU (15 mcg) a day for adults up to age 70 and 800 IU (20 mcg) after 70. Your clinician can check your level if you are at risk of deficiency. See calcium and vitamin D after 40.

A quick reference

Why "more is better" does not apply

Hair, skin and nail supplements often contain large doses of several nutrients at once. That raises a few concerns:

• Little evidence of benefit if you are not deficient.
• Risk of exceeding upper limits when combined with multivitamins and fortified foods.
• Some nutrients can actually cause hair loss in excess, notably very high doses of vitamin A and selenium.
• Masking the real cause. If your thinning is due to female pattern hair loss, a thyroid problem or a medication, a supplement will not fix it and may delay effective treatment.

The ODS guide to dietary supplements offers more general advice on choosing supplements safely.

A smarter approach

1. See a dermatologist or your primary care clinician to identify the cause of thinning. The AAD notes that diagnosis is key to effective treatment.
2. Ask about testing, such as a complete blood count, ferritin, thyroid function and, if appropriate, vitamin D and zinc.
3. Correct any deficiency under medical guidance.
4. Eat a varied diet with enough protein, iron-rich foods, fruits and vegetables.
5. Consider proven treatments, such as topical minoxidil for female pattern hair loss.

Mayo Clinic offers a useful overview of hair loss causes and when to seek care.

The bottom line

Nutrients matter for hair mainly when you are short on them. Iron and protein are the most common nutritional factors in women's hair shedding, and iron is worth checking if you have heavy periods. Biotin deficiency is rare and high-dose biotin can interfere with important lab tests. Zinc and other minerals can be harmful in excess. Get tested, correct real deficiencies and pair good nutrition with proven treatments for the type of hair loss you actually have.

Frequently asked questions

Does biotin help hair grow?

Biotin helps hair only in people who are deficient, which is rare. There is little evidence it helps hair in people with normal biotin levels, and high doses can interfere with lab tests.

Can low iron cause hair loss in women?

Low iron has been associated with hair shedding in some research, and it is common in women with heavy periods. Dermatologists often check ferritin in women with thinning hair.

What blood tests should I get for thinning hair?

Common tests include a complete blood count, ferritin, thyroid function and sometimes vitamin D and zinc. Your clinician will decide based on your symptoms.

Are hair, skin and nail gummies worth it?

For most people who eat a varied diet, there is little evidence they help. They may contain high doses of biotin and other nutrients that can cause problems.