Brittle nails affect an estimated 20% of the population. Three compounds have controlled trial evidence. The effect sizes are modest but real, and the mechanisms are distinct.
Brittle nail syndrome — characterised by onychoschizia (lamellar splitting at the free edge) and onychorrhexis (longitudinal ridging and fragility) — affects an estimated 20% of the population, with women affected more than men. The condition is underresearched relative to its prevalence, which means the supplement market has filled the gap with products of widely varying evidence quality. Three compounds have controlled trial data: biotin, choline-stabilised orthosilicic acid (ch-OSA), and methylsulfonylmethane (MSM).
The nail plate is composed primarily of hard keratin — a sulphur-rich structural protein cross-linked by disulphide bonds. Brittleness results from impaired intercellular adhesion within the nail matrix, abnormalities in keratinisation, or external factors (repeated wetting and drying, chemical exposure, nail polish removers). Secondary causes include thyroid dysfunction, iron deficiency, and dermatological conditions — these should be excluded before attributing brittleness to primary brittle nail syndrome.
Biotin (vitamin B7) is a cofactor for carboxylase enzymes involved in fatty acid synthesis and amino acid metabolism. Its relevance to nail health is thought to involve its role in the synthesis of the lipid components of the nail plate, which contribute to intercellular adhesion. A 1990 trial by Colombo et al. (n=32) — the most cited study in this area — found that biotin supplementation produced a 25% increase in nail plate thickness and reduced splitting in patients with primary brittle nail syndrome, with improvements confirmed by scanning electron microscopy.
The limitation is significant: the Colombo trial was conducted in patients with documented brittle nail syndrome, not the general population. A 2018 review by Lipner and Scher in the Journal of Dermatological Treatment concluded that the evidence for biotin in individuals without biotin deficiency is insufficient to make a general recommendation. Biotin deficiency is rare in adults on a normal diet. The supplement industry's extrapolation from 'biotin deficiency causes nail problems' to 'biotin supplements improve nails in everyone' is not supported.
Silicon is a trace element with a proposed role in collagen and keratin synthesis. The biologically active form is orthosilicic acid (OSA), but OSA is unstable in aqueous solution. Choline-stabilised orthosilicic acid (ch-OSA) is a formulation that delivers bioavailable silicon. A 2005 RCT by Barel et al. (n=50) found that 10 mg Si/day as ch-OSA for 20 weeks produced significantly lower visual analogue scale scores for nail brittleness compared to placebo, with similar improvements in hair brittleness. The effect was modest but statistically significant.
Methylsulfonylmethane (MSM) is an organic sulphur compound. Sulphur is a structural component of keratin — specifically, the cysteine residues that form the disulphide bonds giving nails their hardness. A 2020 double-blind trial by Muizzuddin and Benjamin (n=63) found statistically significant improvements in hair and nail condition with both 1 g/day and 3 g/day of MSM, with the higher dose producing faster and stronger benefits. The trial was conducted in middle-aged women, limiting generalisability.
25% increase in nail plate thickness with biotin (Colombo, 1990). Significant reduction in nail brittleness VAS with ch-OSA at 10 mg Si/day (Barel, 2005). Significant nail condition improvement with MSM at 3 g/day (Muizzuddin, 2020). All three effects are real but modest.
Vitaei verdict
All three compounds have controlled trial evidence for nail brittleness, but the effect sizes are modest and the populations studied are specific. Biotin is most useful in individuals with documented deficiency or primary brittle nail syndrome. ch-OSA (10 mg Si/day) has the cleanest RCT evidence for the general population. MSM (3 g/day) is a reasonable addition given its safety profile and sulphur-keratin rationale. None of these is a substitute for excluding thyroid dysfunction and iron deficiency first.
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