Resfriados (en general)

Biotin from bovine liver supports keratin synthesis required for nail plate integrity; biotin deficiency causes brittle, fragile nails. Iron deficiency (addressed by liver's heme iron) causes koilonychia (spoon-shaped, brittle nails). These two nutrients in bovine liver directly address the most common nutritional causes of nail fragility.

A 2017 open-label trial published in the Journal of Cosmetic Dermatology (PMID 28786550) found that 2.5 g/day of specific bioactive collagen peptides for 24 weeks increased nail growth rate by 12% and reduced the frequency of broken nails by 42% in 25 women with brittle nail syndrome. Collagen peptides supply glycine and proline used in keratin synthesis and nail matrix support.

Copper supports keratin cross-linking via lysyl oxidase and contributes to the structural integrity of nails. Copper deficiency is associated with brittle, malformed nails. This link is established through deficiency evidence and the understood role of copper in connective tissue and keratinized structures.

Horsetail (Equisetum arvense) is the richest plant source of bioavailable silicon, the active constituent underpinning its nail-strengthening use. It has been used traditionally in European herbal medicine for brittle nails and hair. The clinical evidence for nail benefit derives from its silicon content, supported by the ch-OSA trial (Barel et al., 2005) and multiple review acknowledgments.

Iron deficiency is a recognized cause of brittle nails, koilonychia (spoon nails), and impaired nail growth due to reduced oxygen delivery to the nail matrix. Multiple clinical reviews document that iron supplementation with vitamin C can improve nail fragility when ferritin is below 10 ng/mL. This is supported by PMC 11961095, PMC 10987172, and PMC 6994568.

Solubilized (hydrolyzed) keratin supplementation was evaluated in a randomized double-blind placebo-controlled 90-day trial (n=50 women). Subjects receiving 500 mg/day of Cynatine® solubilized keratin with vitamins and minerals showed statistically significant improvements in nail strength and appearance compared to placebo. The Karger review 'Nail Supplements: When, How, and Why?' (2024) lists solubilized keratin among nail supplements with demonstrated clinical benefit.

L-cysteine is an essential component of keratin, the structural protein of nails, contributing to the disulfide cross-links that provide nail hardness and rigidity. Cysteine deficiency can impair nail quality. A 2015 systematic review of NAC in clinical trials noted favorable evidence for nail-biting and related nail/skin-picking behaviors, and cysteine-rich proteins are recognized constituents of nail structure.

L-cystine (the oxidized dimer of L-cysteine) is a key sulfur-containing amino acid in keratin, providing disulfide cross-links that determine nail hardness. A biomineral RCT that included L-cystine alongside L-arginine, glutamic acid, vitamins, and minerals showed effective nail strengthening in onychoschizia patients after 3 months (PMC 11961095, PMC 10987172). A separate RCT evaluated L-cystine with keratin hydrolysate in brittle nail syndrome.

L-methionine is a sulfur-containing amino acid essential for keratin synthesis; the disulfide bonds formed from its cysteine metabolite provide structural rigidity to nails. Adequate methionine is required to produce the keratins that constitute the nail plate. Its role in keratin biochemistry is well-established, and it is a standard ingredient in nail health supplement formulations.

Magnesium is a cofactor in over 300 enzymatic reactions including protein synthesis required for nail plate formation; vertical ridges in nails are associated with magnesium deficiency. Healthline and PMC nutrition reviews identify magnesium deficiency as a contributing factor to nail abnormalities. It was part of a multivitamin formula that demonstrated positive impact on nail growth in a clinical study (PMC 11961095).

Clinical evidence exists specifically for TTO in treating onychomycosis (fungal nail infection), which is the primary nail-related application. A double-blind RCT (n=117) found 100% TTO comparable to 1% clotrimazole, with ~60% partial or full resolution. TTO acts as an antifungal via terpinen-4-ol disruption of fungal cell membranes, with in vitro activity confirmed against major dermatophytes.

MSM is a natural organosulfur compound whose sulfur strengthens keratin disulfide bonds in the nail plate. A 16-week double-blind study by Muizzuddin and Benjamin (n=63 women) found statistically significant expert-assessed improvements in nail appearance and quality at both 1 g and 3 g/day doses. The 2024 Karger review 'Nail Supplements: When, How, and Why?' lists MSM among supplements with demonstrated nail benefits.

Silicon, in its bioavailable form as choline-stabilized orthosilicic acid (ch-OSA), was evaluated in a 20-week double-blind placebo-controlled trial (n=50 women) and showed significantly lower nail brittleness scores vs. placebo. Silicon is a component of the nail plate and supports collagen and glycosaminoglycan synthesis in connective tissue. The 2024 Karger review lists it among four supplements with nail-strength evidence.

Vitamin B12 supports red blood cell formation and enables cells to absorb and use iron; it also supports rapid cell division in the nail matrix. Deficiency is associated with changes in nail shape and color. Multiple clinical reviews (PMC, Seed health, Healthline) identify vitamin B12 deficiency as a cause of nail abnormalities. It was included in a biomineral RCT component for nail improvement.

Biotin has the strongest clinical evidence among supplements for nail strength. Three small uncontrolled trials showed that 2.5 mg/day increased nail thickness by up to 25% and produced firmer, harder nails in 63–91% of participants with brittle nail syndrome. The NIH ODS acknowledges these studies while noting they lack placebo controls and baseline biotin-status data.

Folate is required for DNA synthesis and cell division, both critical for the rapidly dividing nail matrix keratinocytes. Deficiency impairs nail matrix cell production, leading to brittle or abnormal nails. PMC and clinical sources identify folate deficiency as a nutritional cause of nail abnormalities. It is recognized alongside B12 as a cell-division nutrient essential for normal nail growth.

Vitamin C is required for collagen synthesis (hydroxylation of proline and lysine) and enhances non-heme iron absorption, both processes critical for nail bed structural integrity and nail matrix oxygenation. Vitamin C deficiency directly causes brittle nails and slowed nail growth (as in scurvy). It is recognized as a nail-health nutrient by Healthline and multiple clinical reviews, and was an active component in a biomineral RCT showing nail improvement.

Zinc is essential for keratin synthesis and cell division in the nail matrix; zinc deficiency causes nail dystrophy, brittleness, Beau's lines, and slow growth (Cleveland Clinic; Indian J Dermatol Venereol Leprol 2012). Supplementation of 20–30 mg/day corrects nail fragility in deficient individuals according to multiple clinical reviews. PMC 10987172 and PMC 11961095 both document this deficiency-correction benefit.

Bamboo extract is used as a silica supplement traditionally for nail strength and to prevent brittleness. Silicon supports the connective tissue matrix of nails. Western herbal practice since the 1990s and Indian traditional medicine use bamboo for nail health, with mechanistic plausibility from silicon's known role in connective tissue.

Impatiens balsamina has a well-documented traditional use for nail conditions including inflammation of nails, ingrown nails, split nails, and onychomycosis across Chinese, Thai, Malaysian, and Ayurvedic medicine. The application involves direct topical contact of pounded plant material with the affected nail.

Brewer's yeast is traditionally taken for nail strength and integrity, attributed to its biotin, silicon, zinc, and protein content. Biotin has documented clinical evidence for improving nail thickness in brittle nail syndrome, but dedicated trials using yeast as the biotin vehicle for nail outcomes are lacking.