What supplements are recommended for a healthy adult woman with diffuse hair thinning, based on laboratory evaluation?

Supplementation for Female Hair Thinning and Regrowth

For a healthy adult woman with diffuse hair thinning, iron supplementation (35-65 mg elemental iron daily) should be initiated if ferritin is ≤30 μg/L, with a target ferritin ≥60 μg/L, as this addresses the most common and treatable nutritional cause of female hair loss. 1

Initial Laboratory Evaluation

Order the following baseline tests for any woman presenting with hair loss:

• Serum ferritin (single most important test for iron stores) 1
• Complete blood count (CBC) 1
• TSH 1
• Transferrin saturation 1
• Inflammatory markers (CRP or ESR) to interpret ferritin accurately, as ferritin is an acute-phase reactant that can be falsely elevated during inflammation, infection, malignancy, or liver damage 1

Iron Supplementation Protocol

When to Treat

Treat if ferritin ≤30 μg/L without inflammation present, as this defines iron deficiency and is strongly associated with diffuse telogen hair loss in women. 1 If inflammation is present (elevated CRP/ESR), the lower limit of normal ferritin increases to 100 μg/L. 1

• Ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 1
• Multiple studies demonstrate lower ferritin levels in women with diffuse hair loss, telogen effluvium, and androgenetic alopecia 1
• Iron supplementation started within 6 months of hair loss onset results in better prognosis 1

Dosing and Monitoring

• Start with oral iron: 35-65 mg elemental iron daily 1
• Lower dosing or every-other-day dosing may improve tolerability and absorption 1
• Monitor ferritin and hemoglobin every 3 months after starting supplementation 1
• Target ferritin ≥60 μg/L with hemoglobin ≥13.0 g/dL 1
• Consider IV iron for patients with impaired absorption, intolerance to oral iron, or when blood loss exceeds oral repletion capacity 1

Important Caveat

If unexplained iron deficiency is found, check tissue transglutaminase (TTG) antibodies to rule out celiac disease. 1

Additional Micronutrient Considerations

Vitamin D

Check serum 25-hydroxyvitamin D levels in all women with hair loss, particularly if alopecia areata is suspected. 2 Multiple case-control studies show 83.3% vitamin D deficiency rate in alopecia areata patients versus 23.3% in controls, with inverse correlation between vitamin D levels and disease severity. 2

However, for diffuse hair thinning (not alopecia areata), vitamin D supplementation has weaker evidence compared to iron. 3, 2

Zinc

Check serum zinc levels, as zinc deficiency is associated with alopecia areata and serum levels inversely correlate with disease severity. 2 In patients with serum zinc below 70 μg/dL, 50 mg zinc gluconate daily led to therapeutic improvement in 60% of patients at 12 weeks in one small study. 2

Critical limitation: The only double-blind, placebo-controlled trial using 220 mg zinc sulfate twice daily for 3 months showed no improvement despite increased serum zinc levels. 2

RBC Folate

Check RBC folate rather than serum folate for accurate assessment of long-term folate stores, as RBC folate levels are lower in alopecia areata patients and correlate negatively with disease severity. 2

Vitamin B12

Do NOT routinely check vitamin B12 unless pernicious anemia is suspected clinically, as multiple case-control studies found no differences in B12 levels between alopecia areata patients and controls. 2

Evidence Quality and Clinical Context

The evidence for iron supplementation in diffuse telogen hair loss is much stronger than for other micronutrients, with multiple studies showing lower ferritin levels in affected patients. 1 In contrast, evidence for alopecia areata is conflicting, with only 2 of 8 studies supporting an association between iron deficiency and alopecia areata, and this association appears primarily in female subjects. 1, 2

Most evidence comes from small retrospective case-control studies, limiting generalizability, and reverse causation is possible where hair loss may lead to lifestyle changes affecting micronutrient levels. 2 Few randomized controlled trials exist for micronutrient supplementation in alopecia treatment. 2

Proprietary Supplements

A marine protein-based dietary supplement showed significant reduction in hair shedding in the first 3-6 months and increased vellus-like hair diameter after 6 months in premenopausal women with subclinical hair thinning. 4 A gummy supplement containing B vitamins, zinc, and botanical ingredients showed 10.1% increase in hair density at 6 months compared to 2% decrease with placebo. 5

However, these proprietary formulations make it difficult to definitively attribute efficacy to individual supplement components, and they should be considered adjunctive rather than first-line. 2

Practical Algorithm

1. Order ferritin, CBC, TSH, transferrin saturation, and CRP/ESR 1
2. If ferritin ≤30 μg/L (without inflammation): Start 35-65 mg elemental iron daily, target ferritin ≥60 μg/L 1
3. If ferritin normal but hair loss persists: Consider checking serum 25-hydroxyvitamin D, serum zinc, and RBC folate 2
4. Monitor ferritin and hemoglobin every 3 months 1
5. Reassess at 6 months, as iron supplementation started within 6 months of hair loss onset has better prognosis 1