When hair starts thinning, it’s tempting to buy every vitamin that promises a fix. A better first step is finding out whether you’re actually low in something. Here are the deficiencies with the strongest links to hair loss.
Written by Vita Globe Editorial Team | Reviewed against NIH fact sheets and peer-reviewed dermatology reviews
What deficiencies cause thinning hair?
The most studied links are low iron (ferritin), low protein or calories, and zinc deficiency. Vitamin D is also under study, especially in alopecia areata[1][2]. A major review concluded that deficiencies should be checked in people with hair loss, but supplementing without a documented deficiency lacks strong evidence[1].
Caveat: Hair loss has many non-nutritional causes, including genetics, hormones, thyroid problems and stress, so testing beats guessing[7].
Sources: Almohanna 2019 · Guo & Katta 2017 · StatPearls · Verified 2026-09-27
In this article
Can low iron cause hair loss?
Iron is the deficiency most often discussed with hair loss, particularly in women. A 2019 review noted that decreased serum ferritin, the body’s iron store marker, is associated with hair loss in women, although experts still debate what ferritin level matters[1]. An earlier review in the Journal of the American Academy of Dermatology examined the diagnosis and treatment of iron deficiency and its possible relationship to hair loss in depth[4].
People at higher risk of low iron include those with heavy periods, pregnant people and frequent blood donors[3]. Iron deficiency is also a recognized trigger for telogen effluvium, a type of diffuse shedding[7].
Don’t self-treat. The adult upper limit for iron is 45mg a day, and high-dose iron can cause stomach upset and constipation[3]. A ferritin test tells you whether you need it.
Does low protein or dieting thin your hair?
Hair is built from protein, so it makes sense that intake matters. Reviews list protein and calorie deficiency among the nutritional causes of hair loss[2]. Crash diets and low protein intake are recognized triggers of telogen effluvium[7].
In everyday life, this often looks like rapid weight loss, very restrictive eating, or skipping meals for months. For medication-assisted weight loss, see Hair Loss on GLP-1s.
What about zinc?
Zinc deficiency can cause hair loss, along with skin changes and slow wound healing[5]. People at higher risk include vegetarians, people with digestive disorders or after bariatric surgery, and those with alcohol use disorder[5].
The review evidence suggests zinc is necessary for normal hair, and some deficient patients improved with supplementation[1]. More isn’t better, though: the adult upper limit is 40mg a day, and long-term high doses can lower copper levels[5].
Is vitamin D linked to hair loss?
Vitamin D receptors are found in hair follicles, and several studies have found low vitamin D in people with alopecia areata, an autoimmune form of hair loss[1]. Whether supplementing vitamin D improves hair is still being studied[1].
You’re more likely to be low if you get little sun, have darker skin, are older, or have obesity or a condition that affects fat absorption[6]. Adults need 600 IU (15mcg) a day, or 800 IU after age 70, with an upper limit of 4,000 IU[6].
What about biotin, and how should you get tested?
Biotin deficiency does cause hair loss, but it’s rare. Severe deficiency has never been reported in healthy people eating a normal diet[1]. That’s why extra biotin rarely changes hair in people who aren’t low.
Also, too much of some nutrients can cause hair loss: excess vitamin A and selenium have both been linked to shedding[1][2].
Ask your doctor about testing. For persistent shedding, common labs include a complete blood count, iron studies with ferritin, and thyroid function[7]. One review suggests testing based on your diet and risk factors rather than ordering everything[2].
| Nutrient | Link to hair | Who’s at risk |
|---|---|---|
| Iron | Low ferritin associated with hair loss in women[1] | Heavy periods, pregnancy, blood donors[3] |
| Protein/calories | Deficiency linked to hair loss[2] | Crash dieting, restrictive eating |
| Zinc | Deficiency can cause hair loss[5] | Vegetarians, GI conditions[5] |
| Vitamin D | Low levels seen in alopecia areata[1] | Low sun, darker skin, older adults[6] |
| Biotin | Deficiency causes hair loss but is rare[1] | Uncommon in normal diets |
The honest summary
- Iron, protein, zinc and vitamin D have the clearest links to thinning hair[1][2].
- Supplements help when you’re deficient, not as a general fix[1].
- Too much vitamin A or selenium can cause shedding[2].
- A simple blood test is the smartest first step[7].
Our option
Vita Globe Hair, Skin & Nails Gummies with Collagen
Each two-gummy serving provides 5,000mcg of biotin plus vitamins A, C, D, E, B6, B12, folate, zinc, iodine and 20mg of collagen (from fish). It’s non-GMO, gluten-free and tested by an independent third-party lab. It contains fish (tilapia), so it isn’t vegetarian. It isn’t an iron supplement, so it’s not a substitute for treatment if your ferritin is low.
Frequently asked questions
What vitamin deficiency causes hair thinning in females?
Low iron (ferritin) is the most discussed in women[1]. Protein, zinc and vitamin D can also play a role[2].
Can low vitamin D cause hair loss?
Low vitamin D has been found in people with alopecia areata, but whether supplementing helps is still being studied[1].
What blood tests should I get for hair loss?
Common tests include a complete blood count, iron studies with ferritin, and thyroid function[7].
Will hair grow back after fixing a deficiency?
Often, especially with shedding-type hair loss, though regrowth takes months to show.
Can taking too many vitamins cause hair loss?
Yes. Excess vitamin A and selenium have been linked to hair loss[2].
Sources
- Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatol Ther (Heidelb). 2019;9(1):51-70. doi:10.1007/s13555-018-0278-6
- Guo EL, Katta R. Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatol Pract Concept. 2017;7(1):1-10. doi:10.5826/dpc.0701a01
- National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. Updated September 2025. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
- Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. 2006;54(5):824-844. doi:10.1016/j.jaad.2005.11.1104
- National Institutes of Health, Office of Dietary Supplements. Zinc: Fact Sheet for Health Professionals. Updated January 2026. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/
- National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Hughes EC, Syed HA, Saleh D. Telogen Effluvium. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated May 2024. https://www.ncbi.nlm.nih.gov/books/NBK430848/
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
