A handful of supplements can genuinely support hair growth, but only when your body is actually low in the nutrient they provide. For most people eating a balanced diet, popping a hair-growth supplement won’t do much. The supplements with the strongest evidence work by correcting specific deficiencies in iron, vitamin D, or zinc that were disrupting the hair cycle in the first place.
Iron: The Deficiency That Matters Most
Low iron is one of the most well-documented nutritional causes of hair shedding. Your hair follicles need a steady supply of iron to fuel the rapid cell division that produces new strands. When iron stores drop, your body diverts resources to more critical functions, and hair growth slows or stops.
The key measurement is ferritin, the protein that stores iron in your body. In a case-control study of women aged 15 to 45, those with excessive hair shedding (a condition called telogen effluvium) had an average ferritin level of just 16.3 ng/mL, compared to 60.3 ng/mL in women without hair loss. Women with ferritin at or below 30 ng/mL were 21 times more likely to experience this kind of shedding. That’s a striking number, and it means a ferritin level that technically falls within “normal” lab range can still be too low for healthy hair. If you’re losing hair and suspect iron could be the issue, ask your doctor to check ferritin specifically, not just a standard iron panel.
Vitamin D and Hair Follicle Cycling
Vitamin D receptors sit on the cells that form your hair follicles, including the dermal papilla cells that signal new growth and the outer root sheath cells that build the hair strand. The active form of vitamin D binds to these receptors and helps keep follicles in their growth phase longer, while also promoting the proliferation and migration of the cells responsible for producing hair. Animal research shows that removing vitamin D receptors entirely disrupts hair follicle development at a fundamental level.
Vitamin D deficiency is common, particularly in people who spend limited time outdoors or live in northern latitudes. Research has found widespread vitamin D deficiency in people experiencing hair loss, and vitamin D supplementation has shown positive effects in those with alopecia areata, a condition where the immune system attacks hair follicles. If your levels are low, correcting the deficiency can remove a barrier to normal hair cycling. A simple blood test can tell you where you stand.
Zinc’s Role in the Growth Cycle
Zinc is involved in protein synthesis and cell division, both of which are essential for building hair. When zinc levels drop, hair follicles can shift prematurely from their active growth phase into the resting and shedding phases. A nutritional supplement combining hydrolyzed collagen, B vitamins, and zinc sulfate has been shown to improve the ratio of growing hairs to resting hairs after just one month of treatment in people with telogen effluvium. Zinc works best as part of a broader nutritional approach rather than as a standalone fix, and supplementing when you’re already getting enough can cause problems including nausea and copper depletion.
Biotin: Popular but Overhyped
Biotin is the most heavily marketed hair supplement, but the evidence behind it is thin. Only one clinical trial has tested biotin for common hair loss, and while participants reported some improvement in hair density and reduced shedding, the study was small, conducted at a single institution, and relied on participants’ own assessments rather than objective measurements. The American Academy of Dermatology has stated that biotin should not be used as a primary treatment for hair or nail regrowth.
True biotin deficiency is rare in people eating a normal diet. When it does occur, it causes brittle nails, skin rashes, and hair thinning that respond well to supplementation. But taking biotin when you’re not deficient is unlikely to make your hair grow faster or thicker. One AAD dermatologist put it plainly: “Biotin deficiency is rare, and supplements should only be taken if you have a biotin deficiency. Otherwise, they can have adverse effects.”
One of those adverse effects is worth knowing about. The FDA has warned that biotin supplements can interfere with laboratory tests, including the troponin test used to diagnose heart attacks. High-dose biotin can produce falsely low troponin readings, potentially masking a cardiac emergency. If you take biotin supplements, tell your doctor before any blood work.
Saw Palmetto for Hormonal Hair Loss
Saw palmetto works differently from vitamins and minerals. It partially blocks the conversion of testosterone into DHT, the hormone responsible for shrinking hair follicles in androgenetic alopecia (the most common type of hair loss in both men and women). In a 16-week randomized, placebo-controlled trial, oral saw palmetto increased hair density by about 5%, while a topical formulation increased it by roughly 7.6%. Both results were statistically significant compared to placebo. These gains are modest compared to prescription options, but saw palmetto is available over the counter and generally well tolerated. No head-to-head trials against prescription alternatives have been published, so it’s difficult to say exactly how it compares.
Collagen Peptides and Pumpkin Seed Oil
Collagen peptides, particularly those derived from marine sources, have shown promise for increasing hair thickness. In a placebo-controlled study, participants taking bioactive collagen peptides had a statistically significant increase in hair thickness compared to those on placebo. Lab analysis confirmed that the collagen peptides also boosted the proliferation rate of hair follicle cells. Collagen provides amino acids like proline and glycine that serve as building blocks for keratin, the protein hair is made of.
Pumpkin seed oil is another option with preliminary support. A registered clinical trial tested 400 mg per day in men with androgenetic alopecia, though detailed results from that trial have not been published. Earlier Korean research reported meaningful increases in hair count after 24 weeks of supplementation at the same dose, likely through a mild DHT-blocking mechanism similar to saw palmetto.
When Supplements Cause Hair Loss
Taking too much of certain nutrients can actually trigger shedding. Selenium is the clearest example. The tolerable upper intake from supplements is 400 micrograms per day, and going well beyond that causes a recognizable pattern of hair loss, brittle nails, and garlic-scented breath. A CDC report documented a case where a manufacturing error produced tablets containing 31 mg of selenium each (roughly 75 times the upper limit), and the woman taking them developed significant hair loss after just a few weeks. Excess vitamin A can produce similar effects, making it important to check what’s already in your multivitamin before stacking additional supplements.
A Practical Starting Point
The most effective approach is to find out whether you’re actually deficient before spending money on supplements. A blood panel checking ferritin, vitamin D, and zinc covers the most common nutritional causes of hair shedding. If levels are normal, supplements are unlikely to help, and the cause of your hair loss probably lies elsewhere, whether that’s hormonal, stress-related, or genetic.
For hormonal hair loss with no underlying deficiency, saw palmetto and pumpkin seed oil offer modest, low-risk options. Collagen peptides may improve hair thickness regardless of deficiency status, since they supply raw materials for hair protein rather than correcting a shortfall. Biotin, despite its popularity, is worth skipping unless a lab test confirms you’re deficient. As the AAD notes, most people can get everything their hair needs from a well-balanced diet.