Silica (Horsetail / ch-OSA)
Equisetum arvense
Bioavailable silicon studied for skin elasticity, hair and nails
Evidence tier
Preliminary
Research weight
Citations
15 verified / 15
Classification
Joint & Skin
❝
What the evidence says. Early or small human trials; promising but not yet conclusive.
What is Silica (Horsetail / ch-OSA)?
Silica (Horsetail / ch-OSA) (Equisetum arvense) is a joint and skin supplement used for may reduce skin roughness / improve elasticity. NutriDex grades the human evidence as Preliminary. Silicon is a trace element concentrated in connective tissue, where it is thought to support collagen and glycosaminoglycan cross-linking; orthosilicic acid is its most bioavailable form. A few small double-blind RCTs of choline-stabilized orthosilicic acid (ch-OSA) report modest benefits: Barel 2005 found reduced skin roughness and less hair/nail brittleness, while Wickett 2007 found improved hair tensile strength. The evidence base is limited — trials are small, short, and largely industry-funded. Horsetail (the botanical silicon source) is a separate safety issue: it contains thiaminase (which degrades vitamin B1) and trace nicotine, so standardized ch-OSA or thiaminase-free products are preferable.
Purported Benefits
✓May reduce skin roughness / improve elasticity
✓Small trials suggest stronger, thicker hair
✓Some reduction in hair/nail brittleness
✓Supplies bioavailable silicon for connective tissue
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Reduced skin roughness / improved elasticityRests on one small 20-week ch-OSA RCT (n=50) that was industry-funded; not independently replicated. | Preliminary | ↑ benefit · small | 1 |
| Stronger / thicker hairSingle 9-month ch-OSA RCT (n=48) improved tensile strength and cross-sectional area; small and not replicated. | Preliminary | ↑ benefit · small | 1 |
| Reduced hair/nail brittlenessReported as a secondary outcome in the same small Barel 2005 ch-OSA trial; weak standalone evidence. | Preliminary | ↑ benefit · small | 1 |
| Bone collagen formation / bone densitych-OSA raised bone-formation marker PINP in one RCT but did not change BMD; umbrella review found human trials inconsistent at feasible doses. | Mixed | ↔ mixed · small | 3 |
Dosing & Compounds
Typical Dose
ch-OSA ~10 mg Si/day (dose used in trials).
Active Compounds
Safety & Cautions
ch-OSA at ~10 mg Si/day was well tolerated in short trials and is unlikely to harm people with normal kidney function. The main concerns are with horsetail itself: thiaminase can deplete vitamin B1 with prolonged use, and it contains trace nicotine (avoid in pregnancy and when quitting smoking). Choose thiaminase-free standardized products, avoid prolonged/high-dose use, and avoid in renal impairment. Educational only — always check with your doctor or pharmacist before combining Silica (Horsetail / ch-OSA) with any medicine.
Key Studies ★ 15 studies
umbrella review
Pritchard & Nielsen 2024 (umbrella review)
✓ PubMed
Umbrella review in Nutrients found silicon consistently improves bone density and collagen synthesis in animal models, but the effective doses (~139 mg/kg BW/day) far exceed feasible human intake (~12-62 mg/day) and human supplementation trials at modest doses gave inconsistent results.
regulatory opinion
EFSA NDA Panel 2018 (regulatory opinion)
✓ Full text
EFSA scientific opinion concluded there is no safety concern for orthosilicic acid-vanillin complex as a novel-food source of silicon in adult supplements and that silicon is bioavailable from it, while noting silicon essentiality is unestablished and no tolerable upper level could be set.
RCT
Geusens 2021 (RCT)
✓ Full text
12-month exploratory double-blind RCT (21 randomized, 18 per-protocol) in peri-implantitis patients found ch-OSA stabilized peri-implant bone loss and prevented mucosal recession versus significant worsening on placebo.
RCT
Csetti 2021 (RCT)
✓ PubMed
Double-blind randomized trial in 58 stage I hypertensive adults found standardized Equisetum arvense extract lowered systolic and diastolic blood pressure by about 12.6 and 8.1 mmHg respectively, with efficacy and tolerability similar to hydrochlorothiazide.
RCT
Vicente-Zurdo 2021
✓ Full text
In a randomized, double-blind, crossover post-prandial study in 5 healthy men dosed at 21.6 mg silicon, urinary silicon excretion did not differ significantly between an Equisetum arvense orthosilicic acid liquid (32.4%), an aloe-vera OSA liquid (34.6%), and an OSA-maltodextrin powder (27.2%), indicating comparable bioavailability across formulations.
RCT
Teughels 2021 (ch-OSA peri-implantitis RCT)
✓ PubMed
Exploratory randomized, double-blind, placebo-controlled trial, 18 analyzed peri-implantitis patients, ch-OSA vs placebo for 12 months after flap surgery: mucosal recession increased with placebo but not ch-OSA (between-group p<0.01); peri-implant bone levels (IS-BIC, IS-AC) stayed stable with ch-OSA but worsened on placebo (IS-BIC between-group p<0.05).
safety review
LiverTox 2022 (safety review)
✓ Full text
NIH LiverTox classifies horsetail as a probable rare cause of clinically apparent liver injury (likelihood C); conventional oral doses up to ~6 g/day showed no hepatotoxicity in trials and any injury is rare, mild, and self-limiting.
safety assessment
Cosmetic Ingredient Review 2021 (safety assessment)
✓ Source
CIR safety assessment of Equisetum arvense-derived cosmetic ingredients reported few in vivo toxicity studies for most Equisetum species and no consensus on an effective non-toxic dose, while noting crude horsetail contains thiaminase.
RCT
Carneiro 2014 (RCT)
✓ PubMed
Randomized double-blind crossover trial in 36 healthy men found a standardized Equisetum arvense dried extract (900 mg/day) produced a diuretic effect stronger than placebo and comparable to hydrochlorothiazide 25 mg, without significant changes in electrolyte excretion.
RCT
Barel 2005 (RCT)
✓ PubMed
20-week double-blind RCT in 50 women with photodamaged skin; 10 mg Si/day ch-OSA reduced skin roughness, improved mechanical properties, and lowered hair/nail brittleness vs placebo.
RCT
Wickett 2007 (RCT)
✓ PubMed
9-month double-blind RCT in 48 women with fine hair; 10 mg Si/day ch-OSA improved hair tensile strength and increased hair cross-sectional area vs placebo.
RCT
Spector 2008 (RCT)
✓ PubMed
12-month randomized placebo-controlled trial in osteopenic women (184 randomized, 136 completed) found ch-OSA added to calcium/vitamin D3 significantly raised the bone collagen formation marker PINP at the 6 and 12 mg silicon/day doses versus placebo, though lumbar BMD did not change significantly.
Review
Price 2013 (review)
✓ Full text
Review of silicon in connective tissue/bone ranks ch-OSA as an intermediate-bioavailability source but concludes human evidence remains limited and promising rather than established.
Cohort
Jugdaohsingh (Framingham Offspring cohort) 2004
✓ PubMed
Cross-sectional cohort of 2847 adults: higher dietary silicon intake correlated positively and significantly with hip BMD in men and premenopausal women (not postmenopausal women); BMD differed by up to ~10% between highest (>40 mg Si/day) and lowest (<14 mg Si/day) intake quintiles. No association at lumbar spine in most groups.
Cohort
Tucker (Framingham Offspring cohort) 2009
✓ PubMed
Population cohort (1182 men, 1537 women): moderate beer intake associated with 3.4-4.5% greater hip BMD, but after adjustment for silicon intake all beer-BMD differences became non-significant, whereas wine/liquor associations remained, indicating silicon mediates beer's bone benefit.