Various nutrients have been linked to strengthening hair and nails. Scientific studies evaluate the effects of the listed ingredients in vitro or in humans. For each ingredient below, we summarize the results (observed effects, doses, type of study).
Stinging nettle is rich in minerals and traditionally used to stimulate hair growth. Preclinical studies partially support these effects. For example, an ethanolic nettle extract stimulated hair bulb elongation and delayed the transition to the resting phase (catagen) in human follicles in ex vivo culture. However, there is a lack of controlled clinical trials in humans using nettle alone. These results are explained by vasodilation and stimulation of follicles in anagen. In summary, nettle promotes hair growth in organic culture, probably via vasodilation and nutrient supply. Specific human data are scarce.
Horsetail , a natural source of silica, is known for its strong hair and nails. Several studies have focused on silica (often in the form of organic silica) more than on the raw plant. For example, a randomized controlled trial on 48 volunteers tested 10 mg/day of choline-stabilized silica for 9 months. The treated group saw a significant increase in hair strength and cross-sectional area. Similarly, 20 weeks of silica in middle-aged women improved skin elasticity and reduced the brittleness of nails and hair. These studies suggest that bioavailable silica strengthens hair and nails. In practice, formulations combining horsetail and other ingredients have shown benefits. A nail polish containing horsetail extract and MSM strengthened psoriatic nails, reducing their brittleness. A topical solution of nettle and horsetail extract also promoted hair regrowth in alopecia areata. In synthesis, horsetail provides silica, the oral intake of which has improved the quality of hair and nails in humans.
The amino acids L-cystine and L-cysteine are major constituents of hair keratin. Their supplementation has been studied in oral formulas for hair regrowth and nail health. In vitro, a commercially available oral preparation containing L-cystine and vitamins stimulated the proliferation and metabolism of human follicular keratinocytes. In clinical practice, a three-month randomized trial of sixty women with telogen effluvium and brittle nails administered 250 mg/day of L-cystine, with or without 250 mg of hydrolyzed keratin. Both groups showed significant increases in hair density, hair and nail luster, and nail growth rate. These data confirm that oral L-cystine strengthens keratin.
The MSM is an organic source of sulfur, a component of keratin. A double-blind clinical trial in 63 women compared 1 g/day and 3 g/day of MSM for four months. Both dosages improved hair and nail condition, with a faster and more pronounced effect for the higher dose. This suggests that oral MSM strengthens hair and nails by providing sulfur for keratin. It should be noted that the effective doses observed in clinical studies (in grams) are much higher than the levels proposed in some commercial formulas.
Magnesium is involved in many cellular processes, but evidence of a direct effect on hair growth is limited. A ten-week clinical trial in women with polycystic ovary syndrome did not show a clear effect of magnesium on alopecia. In contrast, magnesium deficiency is known to weaken nails, resulting in soft, brittle, and brittle nails. Supplementing magnesium in the absence of deficiency has not shown any proven benefit for hair regrowth, but correcting a deficiency may improve nail quality.
Zinc is essential for cell division and keratin synthesis. A study of patients with alopecia areata showed that oral zinc supplementation (50 mg/day) for 12 weeks increased serum zinc levels, and 66% of subjects experienced partial hair regrowth. Patients who responded to treatment had a greater increase in serum zinc levels. Zinc deficiency is often associated with alopecia areata, and zinc supplementation appears to be particularly beneficial in this setting. Zinc may also help with chronic effluvium. Normal levels are necessary for healthy keratin tissue.
B vitamins , including B5, B6, and B8, are important for cellular metabolism and keratin protein synthesis. Biotin (vitamin B8) has a well-documented role in nails. A clinical trial on women with brittle nails showed that a daily course of biotin increased nail plate thickness by an average of 25%, with 63% of participants reporting significant improvement. Panthenol (a precursor of B5) is often used in hair cosmetics. In vitro, it increases the viability and proliferation of human hair follicle dermal cells, while stimulating factors that promote hair growth. Vitamin B6 has also shown in vitro a beneficial effect on dermal papilla cell proliferation and inhibition of apoptosis. These results indicate that B vitamins promote hair follicle health.
Marine collagen provides bioactive peptides that promote dermal metabolism and, indirectly, hair and nail health. A clinical trial conducted on 25 women for 24 weeks tested 2.5 g/day of a collagen hydrolyzate. The results showed a 12% increase in nail growth rate and a 42% reduction in nail breakage. 64% of participants noted an overall improvement in their nails. These results confirm that oral intake of collagen peptides enhances nail growth. In vitro, marine collagen peptides increased human follicular cell proliferation, activated growth markers (IGF-1, VEGF, Ki67), and inhibited TGF-β1 (hair growth inhibitory factor).
Finally, many formulations combine several of these ingredients. A topical gel containing nettle extracts, other plants, and vitamins significantly decreased the expression of a growth-inhibiting cytokine in human keratinocytes. A nail polish combining horsetail and MSM strengthened psoriatic nails. An oral supplement composed of L-cystine, hydrolyzed keratin, and vitamins improved hair density and nail growth. Marine collagen formulas often also contain biotin and zinc, which maximizes the overall effect on hair and nails.
In conclusion, in vitro and clinical data confirm that most of the listed ingredients have a beneficial role for hair and/or nails. In case of identified deficiency, supplementation often results in a visible benefit on hair regrowth and nail strength.