Hair loss can be linked to low levels of iron, vitamin D, zinc, biotin, or vitamin B12. A blood test can confirm a deficiency.
Nutrients linked to hair loss
- Iron (low ferritin): common in women with heavy periods.
- Vitamin D.
- Zinc.
- Vitamin B12 and folate.
- Biotin: deficiency is rare, and extra biotin doesn’t help most people.
- Protein.
Other causes
Genetics (pattern baldness), thyroid disease, stress, pregnancy, medications and alopecia areata.
Normal shedding
50 to 100 hairs a day.
Testing
Blood tests for ferritin, thyroid (TSH), vitamin D and B12.
Supplements
Don’t take them without a deficiency: too much vitamin A or selenium can cause hair loss.
See a doctor or dermatologist
If shedding is sudden or patchy.
How a deficiency leads to shedding
Hair follicles are among the most active cells in the body, and they divide every 23 to 72 hours. When nutrients are scarce, the body diverts resources to vital organs, and follicles shift early into the resting phase. About 2 to 3 months later, a wave of shedding appears, called telogen effluvium. Because of this delay, hair loss often shows up long after the deficiency began, and regrowth takes 3 to 6 months after levels are corrected.
Iron and ferritin
Iron deficiency is the best documented nutritional cause of diffuse hair loss in women. Ferritin, the iron storage protein, is the usual marker. Many dermatologists look for levels above 40 to 70 ng/mL for hair health, while the lab reference range may start as low as 15 ng/mL. Women with heavy periods, vegetarians, and people with celiac disease are at higher risk. Do not take iron without a blood test, since excess iron is harmful.
Vitamin D, zinc and biotin
- Vitamin D: receptors in follicles help regulate the hair cycle. Low levels have been linked to alopecia areata and telogen effluvium, though trials of supplements for hair are limited.
- Zinc: low zinc causes shedding and brittle hair. The adult upper limit is 40 milligrams a day, and too much zinc causes copper deficiency.
- Biotin: true deficiency is rare, and extra biotin has no proven benefit in people with normal levels. High doses can distort thyroid and troponin lab tests.
Other nutrients and diets
Low protein intake, crash diets and rapid weight loss can all trigger shedding. Hair is made of keratin, and the body needs about 0.8 grams of protein per kilogram of body weight daily. Low vitamin B12 and folate, seen in vegans without supplements and in people with pernicious anemia, can also affect hair. Too much vitamin A (over 10,000 IU daily over long periods) can itself cause hair loss.
Other causes to rule out
Thyroid disease, hormonal changes after pregnancy, PCOS, menopause, stress, medications (such as some blood thinners and antidepressants), autoimmune alopecia areata and genetic pattern hair loss all cause shedding. Pattern hair loss affects about 50% of men by age 50 and roughly 40% of women by age 70, and no vitamin will fix it.
Testing
A doctor can order ferritin, complete blood count, vitamin D, B12, thyroid stimulating hormone and zinc. A pull test and scalp exam help tell types of hair loss apart. Normal shedding is 50 to 100 hairs a day, and losing more than this, or seeing thinning patches, justifies a check.
Treatment and recovery
Treat the cause, not the symptom. Replace deficient nutrients under medical advice, eat enough protein and calories, and treat any underlying condition. Minoxidil 2% to 5% can help pattern hair loss. Expect to wait 3 to 6 months to see change, and up to a year for full recovery.
Timeline of regrowth
Hair shed from nutrient deficiency usually starts 2 to 3 months after the deficiency begins, because the shedding phase lags behind the cause. After correcting the deficit, regrowth takes 3 to 6 months to appear, and 12 months to look full, since scalp hair grows about 1 cm per month. Recheck ferritin and vitamin D 8 to 12 weeks after starting treatment.
Based on data from the American Academy of Dermatology
