Nutritional Deficiencies Associated with Hair Thinning
The most clinically significant nutritional deficiencies linked to hair thinning are iron deficiency (particularly low ferritin), vitamin D deficiency, and zinc deficiency, with iron deficiency having the strongest evidence base, especially for diffuse telogen hair loss in women. 1, 2, 3
Iron Deficiency: The Primary Culprit
Iron deficiency represents the most common and best-established nutritional cause of hair thinning, particularly in premenopausal women. 3, 4
Key Diagnostic Thresholds
- Ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 2, 5
- Ferritin <30 μg/L defines iron deficiency in the absence of inflammation and is strongly associated with telogen hair loss 2, 6
- Iron serves as a cofactor for ribonucleotide reductase, the rate-limiting enzyme in DNA synthesis, making it crucial for rapidly dividing hair follicle cells 3, 4
Evidence Strength by Hair Loss Type
- For diffuse telogen effluvium: Strong evidence - multiple studies consistently show lower ferritin levels in affected patients, with odds ratio of 21.0 for hair loss when ferritin ≤30 ng/mL 6, 7
- For androgenetic alopecia (female pattern hair loss): Moderate evidence - several studies found lower ferritin levels in affected women 1, 3
- For alopecia areata: Conflicting evidence - only 2 of 8 studies supported an association, with positive findings primarily in female subjects 1, 2
Critical Caveat
Ferritin is an acute-phase reactant and can be falsely elevated during infection, inflammation, chronic disease, malignancy, or liver damage, potentially masking true iron deficiency. 2, 3 Always assess inflammatory markers (CRP, ESR) alongside ferritin to aid proper interpretation. 2
Vitamin D Deficiency
Serum vitamin D levels tend to be lower in patients with alopecia areata compared to controls. 1 Vitamin D plays a role in hair follicle cycling and immune regulation, making deficiency a plausible contributor to hair loss. 1
Zinc Deficiency
Most studies identify lower serum zinc levels in patients with alopecia areata compared to controls, with levels inversely associated with disease severity. 1 Zinc functions as a cofactor for numerous enzymes involved in hair follicle development and acts with copper in the antioxidant enzyme superoxide dismutase. 1
Folate (Vitamin B9) Deficiency
Some studies suggest associations between alopecia areata and low red blood cell folate levels, though evidence is mixed. 1 One study found lower RBC folate levels in Iranian patients with alopecia areata, with levels negatively correlated with disease severity (SALT score). 1 However, multiple other case-control studies found no differences in serum folate levels between patients and controls. 1
The discrepancy may relate to measurement method: RBC folate reflects long-term folate status while serum folate indicates recent dietary intake. 1
Vitamin B12 (Cobalamin) Deficiency
Current evidence does not support routine screening for vitamin B12 deficiency in hair loss patients. 1 While case reports exist of patients with both alopecia areata and pernicious anemia (which causes B12 deficiency), multiple case-control studies found no differences in B12 levels between alopecia areata patients and controls. 1
Biotin Deficiency
Biotin deficiency can cause hair loss in rare cases, typically from genetic abnormalities or malabsorption from excessive raw egg consumption. 1 However, studies of biotin supplementation for alopecia areata are extremely limited, with only one study using combination therapy (preventing conclusions about biotin's singular efficacy). 1
Other Micronutrients with Insufficient Evidence
Copper, Magnesium, and Selenium
The current paucity of studies precludes any conclusions about these minerals' role in hair loss. 1 Most studies found no differences in serum copper or magnesium levels between alopecia areata patients and controls. 1 For selenium, two studies yielded conflicting results. 1
Vitamin E and Beta-Carotene
Limited evidence suggests possible associations with oxidative stress in alopecia areata, but data are too sparse for clinical recommendations. 1 One Egyptian study found lower vitamin E levels in alopecia areata patients, while a Turkish study found lower beta-carotene but normal vitamin E. 1
Clinical Approach to Testing
The American Academy of Dermatology recommends ordering CBC, serum ferritin, TSH, and transferrin saturation as baseline tests for any woman presenting with hair loss. 2, 5
When to Test Beyond Iron
- Test vitamin D and zinc if alopecia areata is present and initial workup is unrevealing 1
- Consider tissue transglutaminase antibodies if unexplained iron deficiency is found to rule out celiac disease 2
- Routine testing for B vitamins, copper, magnesium, or selenium is not recommended based on current evidence 1
Treatment Timing Matters
Iron supplementation started within 6 months of hair loss onset results in better prognosis. 2, 3, 5 Hair loss from iron deficiency develops gradually over months, not acutely. 2, 5