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Hair growth supplements are a billion-dollar industry, yet most people taking them can't tell if they're working. They only help when they address the specific cause of your hair loss. Iron, zinc, and vitamin D reduce shedding if you're deficient; marine protein supplements have the strongest clinical evidence overall; and biotin does almost nothing in healthy people. Here's what the research shows.
Superpower's Baseline Blood Panel tests ferritin, vitamin D, hemoglobin, and thyroid markers, the key drivers behind most hair loss, so you know exactly what to address before spending money on supplements.
What Hair Growth Supplements Actually Do in the Body
Hair follicles are metabolically demanding. They cycle through growth phases requiring a steady supply of amino acids, vitamins, minerals, and signaling molecules. When the body runs short on these inputs, follicles shift prematurely from the growth phase (anagen) into the resting phase (telogen), triggering increased shedding and reduced density.
Hair growth supplements fall into three main categories:
- Nutrient deficiency correction, iron, zinc, vitamin D: work when you're deficient, do nothing when you're not
- Hormonal pathway modulation, saw palmetto and other DHT inhibitors: work for androgenetic alopecia
- General "nourishing" formulas, biotin, collagen, keratin peptides: heavily marketed but largely unproven in healthy people
The first two categories have real biological rationale. The third is mostly marketing.
Ferritin, the storage form of iron, is essential for DNA synthesis in rapidly dividing follicle cells. Low ferritin, below 30–40 ng/mL, can trigger diffuse hair shedding even when hemoglobin stays normal. Vitamin D receptors sit inside hair follicles, and deficiency is linked to telogen effluvium and alopecia areata. Supplementing these nutrients only works if you're deficient. Add more when your levels are already fine, and you won't grow a single extra strand.
Saw palmetto belongs to the second category. It inhibits 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). DHT miniaturizes follicles in androgenetic alopecia, the most common form of hair loss in both men and women. Blocking this pathway can slow progression, though the effect is modest compared to prescription options.
Biotin plays a role in keratin infrastructure, but biotin deficiency is rare in people eating a varied diet. Supplementing it when you're not deficient doesn't enhance hair growth. Collagen provides amino acids like glycine and proline, but no direct pathway directs those fragments preferentially to hair follicles over other tissues.
Marine protein complexes
The clearest exception to that third category is marine protein supplements, fish-derived proteins combined with polysaccharides and vitamins. Clinical trials on formulations like Viviscal show measurable increases in terminal hair count and reductions in shedding over three to six months. The proposed mechanism involves amino acids and glycosaminoglycans supporting the extracellular matrix around follicles, though the exact pathway isn't fully understood.
How Hair Growth Supplements Affect Follicle Function and Systemic Pathways
Hair follicles respond to circulating hormones, inflammatory signals, nutrient availability, and oxidative stress. Hair growth supplements that work do so by addressing one or more of these inputs directly.
Iron and oxygen delivery
Your body requires iron for hemoglobin synthesis, which carries oxygen to tissues. Hair follicles have high metabolic rates and are sensitive to oxygen shortage. Low ferritin impairs follicle cell proliferation even before anemia develops. Women with chronic telogen effluvium often show ferritin levels below 40 ng/mL.
Supplementing iron in these cases can reduce shedding, but results take months. Follicles must complete their current cycle before entering a new growth phase. For more on what your levels should be, see optimal ferritin ranges.
Zinc and keratin synthesis
Zinc is a cofactor for over 300 enzymes, including those involved in protein synthesis and cell division. Hair follicles need zinc to produce keratin, the structural protein that makes up hair shafts. Zinc deficiency causes brittle hair, slowed growth, and telogen effluvium. Supplementing zinc when deficient restores normal follicle function.
Excess zinc creates a different problem, it interferes with copper absorption and can disrupt immune function. Always test before you supplement.
Vitamin D and follicle cycling
Hair follicles express vitamin D receptors, and vitamin D signaling influences the transition between growth phases. Deficiency is associated with alopecia areata and telogen effluvium. Supplementing vitamin D when levels are low may support normal cycling, though the evidence is less robust than for iron or zinc.
DHT inhibition and androgenetic alopecia
Saw palmetto inhibits 5-alpha-reductase, reducing DHT production. In a 16-week randomized controlled trial, oral and topical saw palmetto reduced hair fall by up to 29% and improved hair growth in men and women with androgenetic alopecia. In a 2002 placebo-controlled trial of 26 men, 60% taking a 5-alpha-reductase inhibitor containing saw palmetto showed improvement at the final visit.
Marine proteins and follicle support
Marine protein supplements containing fish extracts, polysaccharides, and added nutrients show consistent results in clinical trials. A double-blind, placebo-controlled study found that women taking a marine protein supplement had significant increases in terminal hair count (P < 0.0001) and reductions in shedding (P = 0.002) over three months. The likely mechanism involves amino acids and glycosaminoglycans that support the follicle microenvironment.
What Clinical Research Actually Shows About Hair Growth Supplements
The evidence base for hair growth supplements is uneven. Some ingredients have been studied in rigorous trials. Others are marketed on mechanistic plausibility or weak observational data alone.
Biotin: overhyped and under-evidenced
Despite its ubiquity in hair supplements, biotin has virtually no evidence for hair growth in healthy people. A 2017 review in Skin Appendage Disorders concluded that biotin supplementation only benefits people with documented biotin deficiency, a rare condition typically caused by genetic disorders, prolonged antibiotic use, or severe malnutrition. In healthy people, excess biotin is simply excreted in urine.
No randomized controlled trials show that biotin improves hair growth in people with normal biotin status. The myth persists because biotin is cheap, well-tolerated, and heavily marketed.
Marine protein supplements: the strongest evidence
Marine protein supplements have the most consistent clinical support of any category. A 2015 study in Dermatology Research and Practice evaluated a marine protein complex in 60 women with self-perceived thinning hair. After three months, the supplement group showed significant increases in terminal hair count versus placebo (P < 0.0001) and significantly less shedding (P = 0.002).
A 2016 study in men with thinning hair found significant increases in total hair count, density, and terminal hair density after six months (P = 0.001). These formulations typically combine fish-derived proteins, polysaccharides, and vitamin C. The marine protein complex itself appears to be the active driver.
Saw palmetto: moderate evidence for androgenetic alopecia
Saw palmetto has been studied in several small trials with generally positive results. A 2023 randomized, placebo-controlled study of 80 subjects found oral and topical saw palmetto reduced hair fall by up to 29% and improved hair density over 16 weeks.
A 2020 systematic review pooling five RCTs and two cohort studies reported 60% improvement in overall hair quality and increased density in 83.3% of subjects, though small sample sizes and short follow-up periods limit the conclusions. The effect is real but modest, saw palmetto is not as effective as prescription DHT blockers like finasteride.
Iron, zinc, and vitamin D: effective only when deficient
Supplementing iron, zinc, or vitamin D improves hair growth only in people with documented deficiencies. A 2019 review in Dermatology and Therapy found that low ferritin, zinc, and vitamin D levels are common in people with telogen effluvium and alopecia areata. Correcting these deficiencies can reduce shedding and support normal follicle function.
Supplementing these nutrients when your levels are already adequate does nothing for hair growth, and can cause harm. Iron overload damages organs. Excess zinc interferes with copper absorption. High-dose vitamin D can cause hypercalcemia.
Collagen: emerging but limited evidence
Collagen supplements are heavily marketed for hair, skin, and nails, but direct evidence for hair growth remains limited. Collagen breaks down into amino acids and small peptides during digestion, and no well-established mechanism directs those fragments preferentially to hair follicles.
Emerging research is beginning to challenge this picture. A 2024 clinical trial found that 12 weeks of oral hydrolysed collagen improved scalp and hair condition. A 2023 RCT found that a supplement combining hydrolyzed marine collagen, amino acids, iron, and selenium improved outcomes in subjects with androgenetic alopecia and telogen effluvium.
In both studies, collagen was paired with other active ingredients, isolating its independent contribution isn't possible from current data. If you want to try it, whole body collagen provides a well-formulated option.
When and How to Take Hair Growth Supplements
Timing, dose, and form matter. Hair growth supplements work best when they address a documented deficiency or target a specific pathway relevant to your type of hair loss.
Iron: dose and form
Iron supplementation is most effective when ferritin is below 40 ng/mL. The typical dose is 65–100 mg of elemental iron daily, taken with vitamin C to enhance absorption. Iron bisglycinate is better tolerated than ferrous sulfate and causes less gastrointestinal upset.
Take iron on an empty stomach if tolerated, or with food if nausea occurs. Avoid calcium, tea, or coffee at the same time, they inhibit absorption. Recheck ferritin after three months to assess your response.
Zinc: balancing intake
Zinc supplementation makes sense when serum zinc is low or dietary intake is inadequate. A typical dose is 15–30 mg daily. Zinc bisglycinate is well-absorbed and less likely to cause nausea than zinc sulfate. Don't exceed 40 mg daily, excess zinc can interfere with copper absorption and cause immune dysfunction. Take it with food to minimize gastrointestinal side effects.
Vitamin D: correcting deficiency
Vitamin D supplementation works when serum 25-hydroxyvitamin D is below 30 ng/mL. A typical maintenance dose is 1,000–2,000 IU daily, with higher doses (5,000–10,000 IU) for correction under medical supervision. Vitamin D3 is more effective than D2 at raising serum levels. Take it with a fat-containing meal for optimal absorption. Recheck levels after three months.
Marine protein supplements: consistency is key
Marine protein supplements like Viviscal are typically taken twice daily with meals. Clinical trials show results after three to six months of consistent use. Most people tolerate these formulations well, though anyone with a fish allergy should avoid them. Efficacy varies by brand because the active ingredients are proprietary blends.
Saw palmetto: oral and topical options
Saw palmetto is available in oral capsules (160–320 mg daily) and topical formulations. Clinical trials show modest success with both routes. Oral saw palmetto is generally well-tolerated, though some people experience mild gastrointestinal upset. Expect three to six months before results become apparent.
Why the Same Supplement Works Differently for Different People
Hair loss is not a single condition. It's a symptom with multiple causes, and hair growth supplements only work when they address the specific underlying driver.
Nutrient status at baseline
If your ferritin is 15 ng/mL, iron supplementation will likely reduce shedding. If your ferritin is 80 ng/mL, iron won't help and may cause harm. The same logic applies to zinc, vitamin D, and B vitamins. Testing baseline levels before supplementing reveals whether you have a deficiency worth correcting.
Type of hair loss
Androgenetic alopecia responds to DHT inhibitors like saw palmetto. Telogen effluvium responds to correcting nutrient deficiencies or removing triggers like stress or medication. Alopecia areata is an autoimmune condition that doesn't respond to most supplements. Taking a generic hair growth formula without knowing your diagnosis is unlikely to produce results.
Hormonal and metabolic context
Women with polycystic ovary syndrome (PCOS) often carry elevated androgens that contribute to hair thinning. Supplements that lower androgens or block DHT may help in this context. Postmenopausal women experience thinning from declining estrogen shifting the androgen-to-estrogen ratio, supplements alone rarely reverse this, though correcting nutrient deficiencies can slow progression.
Gut health and absorption
Nutrient absorption depends on gut health. People with celiac disease, inflammatory bowel disease, or SIBO may not absorb oral supplements effectively. In these cases, fixing the underlying gut condition matters more than increasing supplement doses.
Medication interactions
Some medications interfere with nutrient absorption. Proton pump inhibitors reduce iron and B12 absorption. Metformin lowers B12 levels. Oral contraceptives can deplete folate and B vitamins. If you take medications that affect nutrient status, supplementation may be necessary even when dietary intake looks adequate.
How to Use Biomarkers to Guide Supplement Decisions
Testing baseline biomarkers before starting hair growth supplements removes guesswork. You get to see exactly which deficiencies are present, and track whether they resolve over time.
Ferritin: the most important marker for hair loss
Ferritin reflects iron stores and is the single most useful biomarker for evaluating hair loss. Levels below 30–40 ng/mL are associated with increased shedding even when hemoglobin is normal. If ferritin is low, iron supplementation is appropriate. If ferritin is adequate, iron won't help and may cause harm. Recheck after three months of supplementation to assess response.
Vitamin D: widespread deficiency, easy to correct
Vitamin D deficiency is common, especially in people who live at northern latitudes or spend little time outdoors. Levels below 30 ng/mL are considered deficient. Supplementing when deficient may support normal hair follicle cycling, though the evidence is less robust than for iron. Recheck after three months to confirm adequate repletion.
Zinc: less commonly tested, but relevant
Serum zinc isn't routinely tested, but it's worth checking if you have unexplained hair loss, brittle nails, or poor wound healing. Zinc deficiency is more common in vegetarians, people with malabsorption disorders, and those on certain medications. If zinc is low, supplementation helps. If zinc is normal, supplementing won't improve hair growth.
Thyroid function: ruling out hormonal causes
TSH, free T4, and thyroid antibodies help rule out hypothyroidism and autoimmune thyroid disease, both of which cause hair thinning. If thyroid function is abnormal, treating the underlying condition matters more than any supplement.
Hemoglobin and complete blood count
Hemoglobin, hematocrit, and red blood cell indices reveal whether anemia is present. Anemia causes diffuse hair shedding alongside fatigue. If anemia is present, identifying the cause, iron deficiency, B12 deficiency, or chronic disease, guides the right treatment approach.
What Hair Growth Supplements Actually Do in the Body
Hair follicles are metabolically demanding. They cycle through growth phases requiring a steady supply of amino acids, vitamins, minerals, and signaling molecules. When the body runs short on these inputs, follicles shift prematurely from the growth phase (anagen) into the resting phase (telogen), triggering increased shedding and reduced density.
Hair growth supplements fall into three main categories:
- Nutrient deficiency correction, iron, zinc, vitamin D: work when you're deficient, do nothing when you're not
- Hormonal pathway modulation, saw palmetto and other DHT inhibitors: work for androgenetic alopecia
- General "nourishing" formulas, biotin, collagen, keratin peptides: heavily marketed but largely unproven in healthy people
The first two categories have real biological rationale. The third is mostly marketing.
Ferritin, the storage form of iron, is essential for DNA synthesis in rapidly dividing follicle cells. Low ferritin, below 30–40 ng/mL, can trigger diffuse hair shedding even when hemoglobin stays normal. Vitamin D receptors sit inside hair follicles, and deficiency is linked to telogen effluvium and alopecia areata. Supplementing these nutrients only works if you're deficient. Add more when your levels are already fine, and you won't grow a single extra strand.
Saw palmetto belongs to the second category. It inhibits 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). DHT miniaturizes follicles in androgenetic alopecia, the most common form of hair loss in both men and women. Blocking this pathway can slow progression, though the effect is modest compared to prescription options.
Biotin plays a role in keratin infrastructure, but biotin deficiency is rare in people eating a varied diet. Supplementing it when you're not deficient doesn't enhance hair growth. Collagen provides amino acids like glycine and proline, but no direct pathway directs those fragments preferentially to hair follicles over other tissues.
Marine protein complexes
The clearest exception to that third category is marine protein supplements, fish-derived proteins combined with polysaccharides and vitamins. Clinical trials on formulations like Viviscal show measurable increases in terminal hair count and reductions in shedding over three to six months. The proposed mechanism involves amino acids and glycosaminoglycans supporting the extracellular matrix around follicles, though the exact pathway isn't fully understood.
How Hair Growth Supplements Affect Follicle Function and Systemic Pathways
Hair follicles respond to circulating hormones, inflammatory signals, nutrient availability, and oxidative stress. Hair growth supplements that work do so by addressing one or more of these inputs directly.
Iron and oxygen delivery
Your body requires iron for hemoglobin synthesis, which carries oxygen to tissues. Hair follicles have high metabolic rates and are sensitive to oxygen shortage. Low ferritin impairs follicle cell proliferation even before anemia develops. Women with chronic telogen effluvium often show ferritin levels below 40 ng/mL.
Supplementing iron in these cases can reduce shedding, but results take months. Follicles must complete their current cycle before entering a new growth phase. For more on what your levels should be, see optimal ferritin ranges.
Zinc and keratin synthesis
Zinc is a cofactor for over 300 enzymes, including those involved in protein synthesis and cell division. Hair follicles need zinc to produce keratin, the structural protein that makes up hair shafts. Zinc deficiency causes brittle hair, slowed growth, and telogen effluvium. Supplementing zinc when deficient restores normal follicle function.
Excess zinc creates a different problem, it interferes with copper absorption and can disrupt immune function. Always test before you supplement.
Vitamin D and follicle cycling
Hair follicles express vitamin D receptors, and vitamin D signaling influences the transition between growth phases. Deficiency is associated with alopecia areata and telogen effluvium. Supplementing vitamin D when levels are low may support normal cycling, though the evidence is less robust than for iron or zinc.
DHT inhibition and androgenetic alopecia
Saw palmetto inhibits 5-alpha-reductase, reducing DHT production. In a 16-week randomized controlled trial, oral and topical saw palmetto reduced hair fall by up to 29% and improved hair growth in men and women with androgenetic alopecia. In a 2002 placebo-controlled trial of 26 men, 60% taking a 5-alpha-reductase inhibitor containing saw palmetto showed improvement at the final visit.
Marine proteins and follicle support
Marine protein supplements containing fish extracts, polysaccharides, and added nutrients show consistent results in clinical trials. A double-blind, placebo-controlled study found that women taking a marine protein supplement had significant increases in terminal hair count (P < 0.0001) and reductions in shedding (P = 0.002) over three months. The likely mechanism involves amino acids and glycosaminoglycans that support the follicle microenvironment.
What Clinical Research Actually Shows About Hair Growth Supplements
The evidence base for hair growth supplements is uneven. Some ingredients have been studied in rigorous trials. Others are marketed on mechanistic plausibility or weak observational data alone.
Biotin: overhyped and under-evidenced
Despite its ubiquity in hair supplements, biotin has virtually no evidence for hair growth in healthy people. A 2017 review in Skin Appendage Disorders concluded that biotin supplementation only benefits people with documented biotin deficiency, a rare condition typically caused by genetic disorders, prolonged antibiotic use, or severe malnutrition. In healthy people, excess biotin is simply excreted in urine.
No randomized controlled trials show that biotin improves hair growth in people with normal biotin status. The myth persists because biotin is cheap, well-tolerated, and heavily marketed.
Marine protein supplements: the strongest evidence
Marine protein supplements have the most consistent clinical support of any category. A 2015 study in Dermatology Research and Practice evaluated a marine protein complex in 60 women with self-perceived thinning hair. After three months, the supplement group showed significant increases in terminal hair count versus placebo (P < 0.0001) and significantly less shedding (P = 0.002).
A 2016 study in men with thinning hair found significant increases in total hair count, density, and terminal hair density after six months (P = 0.001). These formulations typically combine fish-derived proteins, polysaccharides, and vitamin C. The marine protein complex itself appears to be the active driver.
Saw palmetto: moderate evidence for androgenetic alopecia
Saw palmetto has been studied in several small trials with generally positive results. A 2023 randomized, placebo-controlled study of 80 subjects found oral and topical saw palmetto reduced hair fall by up to 29% and improved hair density over 16 weeks.
A 2020 systematic review pooling five RCTs and two cohort studies reported 60% improvement in overall hair quality and increased density in 83.3% of subjects, though small sample sizes and short follow-up periods limit the conclusions. The effect is real but modest, saw palmetto is not as effective as prescription DHT blockers like finasteride.
Iron, zinc, and vitamin D: effective only when deficient
Supplementing iron, zinc, or vitamin D improves hair growth only in people with documented deficiencies. A 2019 review in Dermatology and Therapy found that low ferritin, zinc, and vitamin D levels are common in people with telogen effluvium and alopecia areata. Correcting these deficiencies can reduce shedding and support normal follicle function.
Supplementing these nutrients when your levels are already adequate does nothing for hair growth, and can cause harm. Iron overload damages organs. Excess zinc interferes with copper absorption. High-dose vitamin D can cause hypercalcemia.
Collagen: emerging but limited evidence
Collagen supplements are heavily marketed for hair, skin, and nails, but direct evidence for hair growth remains limited. Collagen breaks down into amino acids and small peptides during digestion, and no well-established mechanism directs those fragments preferentially to hair follicles.
Emerging research is beginning to challenge this picture. A 2024 clinical trial found that 12 weeks of oral hydrolysed collagen improved scalp and hair condition. A 2023 RCT found that a supplement combining hydrolyzed marine collagen, amino acids, iron, and selenium improved outcomes in subjects with androgenetic alopecia and telogen effluvium.
In both studies, collagen was paired with other active ingredients, isolating its independent contribution isn't possible from current data. If you want to try it, whole body collagen provides a well-formulated option.
When and How to Take Hair Growth Supplements
Timing, dose, and form matter. Hair growth supplements work best when they address a documented deficiency or target a specific pathway relevant to your type of hair loss.
Iron: dose and form
Iron supplementation is most effective when ferritin is below 40 ng/mL. The typical dose is 65–100 mg of elemental iron daily, taken with vitamin C to enhance absorption. Iron bisglycinate is better tolerated than ferrous sulfate and causes less gastrointestinal upset.
Take iron on an empty stomach if tolerated, or with food if nausea occurs. Avoid calcium, tea, or coffee at the same time, they inhibit absorption. Recheck ferritin after three months to assess your response.
Zinc: balancing intake
Zinc supplementation makes sense when serum zinc is low or dietary intake is inadequate. A typical dose is 15–30 mg daily. Zinc bisglycinate is well-absorbed and less likely to cause nausea than zinc sulfate. Don't exceed 40 mg daily, excess zinc can interfere with copper absorption and cause immune dysfunction. Take it with food to minimize gastrointestinal side effects.
Vitamin D: correcting deficiency
Vitamin D supplementation works when serum 25-hydroxyvitamin D is below 30 ng/mL. A typical maintenance dose is 1,000–2,000 IU daily, with higher doses (5,000–10,000 IU) for correction under medical supervision. Vitamin D3 is more effective than D2 at raising serum levels. Take it with a fat-containing meal for optimal absorption. Recheck levels after three months.
Marine protein supplements: consistency is key
Marine protein supplements like Viviscal are typically taken twice daily with meals. Clinical trials show results after three to six months of consistent use. Most people tolerate these formulations well, though anyone with a fish allergy should avoid them. Efficacy varies by brand because the active ingredients are proprietary blends.
Saw palmetto: oral and topical options
Saw palmetto is available in oral capsules (160–320 mg daily) and topical formulations. Clinical trials show modest success with both routes. Oral saw palmetto is generally well-tolerated, though some people experience mild gastrointestinal upset. Expect three to six months before results become apparent.
Why the Same Supplement Works Differently for Different People
Hair loss is not a single condition. It's a symptom with multiple causes, and hair growth supplements only work when they address the specific underlying driver.
Nutrient status at baseline
If your ferritin is 15 ng/mL, iron supplementation will likely reduce shedding. If your ferritin is 80 ng/mL, iron won't help and may cause harm. The same logic applies to zinc, vitamin D, and B vitamins. Testing baseline levels before supplementing reveals whether you have a deficiency worth correcting.
Type of hair loss
Androgenetic alopecia responds to DHT inhibitors like saw palmetto. Telogen effluvium responds to correcting nutrient deficiencies or removing triggers like stress or medication. Alopecia areata is an autoimmune condition that doesn't respond to most supplements. Taking a generic hair growth formula without knowing your diagnosis is unlikely to produce results.
Hormonal and metabolic context
Women with polycystic ovary syndrome (PCOS) often carry elevated androgens that contribute to hair thinning. Supplements that lower androgens or block DHT may help in this context. Postmenopausal women experience thinning from declining estrogen shifting the androgen-to-estrogen ratio, supplements alone rarely reverse this, though correcting nutrient deficiencies can slow progression.
Gut health and absorption
Nutrient absorption depends on gut health. People with celiac disease, inflammatory bowel disease, or SIBO may not absorb oral supplements effectively. In these cases, fixing the underlying gut condition matters more than increasing supplement doses.
Medication interactions
Some medications interfere with nutrient absorption. Proton pump inhibitors reduce iron and B12 absorption. Metformin lowers B12 levels. Oral contraceptives can deplete folate and B vitamins. If you take medications that affect nutrient status, supplementation may be necessary even when dietary intake looks adequate.
How to Use Biomarkers to Guide Supplement Decisions
Testing baseline biomarkers before starting hair growth supplements removes guesswork. You get to see exactly which deficiencies are present, and track whether they resolve over time.
Ferritin: the most important marker for hair loss
Ferritin reflects iron stores and is the single most useful biomarker for evaluating hair loss. Levels below 30–40 ng/mL are associated with increased shedding even when hemoglobin is normal. If ferritin is low, iron supplementation is appropriate. If ferritin is adequate, iron won't help and may cause harm. Recheck after three months of supplementation to assess response.
Vitamin D: widespread deficiency, easy to correct
Vitamin D deficiency is common, especially in people who live at northern latitudes or spend little time outdoors. Levels below 30 ng/mL are considered deficient. Supplementing when deficient may support normal hair follicle cycling, though the evidence is less robust than for iron. Recheck after three months to confirm adequate repletion.
Zinc: less commonly tested, but relevant
Serum zinc isn't routinely tested, but it's worth checking if you have unexplained hair loss, brittle nails, or poor wound healing. Zinc deficiency is more common in vegetarians, people with malabsorption disorders, and those on certain medications. If zinc is low, supplementation helps. If zinc is normal, supplementing won't improve hair growth.
Thyroid function: ruling out hormonal causes
TSH, free T4, and thyroid antibodies help rule out hypothyroidism and autoimmune thyroid disease, both of which cause hair thinning. If thyroid function is abnormal, treating the underlying condition matters more than any supplement.
Hemoglobin and complete blood count
Hemoglobin, hematocrit, and red blood cell indices reveal whether anemia is present. Anemia causes diffuse hair shedding alongside fatigue. If anemia is present, identifying the cause, iron deficiency, B12 deficiency, or chronic disease, guides the right treatment approach.
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