Evidence Review
Silicon and Bone Mineral Density
The strongest human evidence for silicon's role in bone health comes from the Framingham Offspring cohort study (Jugdaohsingh et al., 2004) [1]. This observational study in 2,847 adults found that dietary Si intake was a significant positive predictor of cortical bone mineral density (BMD) in men (p < 0.001) and premenopausal women (p = 0.04), independent of calcium, phosphorus, and other established bone nutrients. The association was not significant in postmenopausal women not on hormone therapy, suggesting an interaction with estrogen status.
Animal evidence for horsetail extract specifically was provided by Arbabzadegan et al. (2019) [6], who found that E. arvense extract significantly increased femur and tibia BMD in Wistar rats compared to untreated controls, as measured by digital radiography. A separate study in an ovariectomized rat model of osteoporosis (Kotwal & Badole, 2016) found E. arvense combined with calcium and vitamin D3 showed anabolic bone effects comparable to the combination supplementation alone, but the herb appeared to add some incremental benefit.
Limitations: Human RCT data for horsetail extract on bone density are lacking. The Framingham data reflect dietary silicon broadly (from grains, vegetables, and water) — not horsetail supplementation specifically. Translating animal and epidemiological data to clinical practice requires caution.
Hair and Nail Silicon RCTs
Barel et al. (2005) [3] conducted a double-blind, placebo-controlled trial (n=50) using 10 mg/day of choline-stabilized orthosilicic acid (ch-OSA) for 20 weeks in women with photodamaged skin. The silicon group showed significant improvements in nail brittleness scores and skin roughness vs. placebo. Hair brittleness also trended toward improvement.
Wickett et al. (2007) [2] extended this with a 9-month double-blind RCT in 48 women with fine hair. The ch-OSA group (10 mg Si/day) showed statistically significant improvements in hair tensile break load (+13% vs. placebo, p < 0.05), elasticity, and hair cross-sectional area. This is a robust, well-designed trial with clinically meaningful outcomes.
Important note: Both trials used ch-OSA — a specific bioavailable silicon form — not horsetail tea directly. Horsetail is a food source of silicic acid with likely lower and more variable bioavailability per dose. The trials establish that silicon bioactivity for hair and nails is real; whether tea or standard extracts deliver equivalent doses requires individual consideration.
Anti-Inflammatory Mechanisms
Martins Do Monte et al. (2004) [4] demonstrated that a hydroalcoholic extract of E. arvense stems reduced carrageenan-induced paw edema by 25–30% at 50 mg/kg in mice, with peak activity at 3–4 hours post-challenge, consistent with inhibition of the prostaglandin-mediated phase of inflammation. The extract also showed antinociceptive effects in the writhing and hot-plate tests.
A more mechanistic in vitro study (Steinborn et al., 2018) established that E. arvense preparations suppress lymphocyte proliferation and activation via an IL-2-dependent pathway, with activity found in both aqueous and ethanolic fractions. Importantly, the flavonoid fraction (not the silica-rich fraction) drove most of the lymphocyte suppression, suggesting the plant's anti-inflammatory properties extend beyond its mineral content.
Strength of evidence: Anti-inflammatory evidence is primarily animal and in vitro. Clinical anti-inflammatory applications are not yet supported by human RCTs.
Wound Healing
Asgharikhatooni et al. (2015) [5] conducted the most rigorous human clinical trial: a randomized, placebo-controlled study in women who received topical 3% E. arvense ointment vs. placebo after episiotomy (n=108). The horsetail group showed significantly faster wound healing (assessed via REEDA scale at days 5, 10) and lower pain scores (VAS) compared to the Vaseline placebo group. This is a high-quality clinical trial with a meaningful patient population.
Animal wound-healing studies (Ozay et al., 2010) corroborated these findings, showing 95–99% wound closure in rats treated with E. arvense ointment alongside enhanced angiogenesis and granulation tissue formation.
Clinical relevance: Topical horsetail is the best-supported application, particularly for tissue repair. The mechanism likely involves both silica (collagen synthesis) and flavonoid-mediated reduction of wound-site inflammation.
Overall Evidence Quality
| Application |
Evidence Level |
Human RCT? |
| Hair/nail strength (silicon) |
Moderate |
Yes (ch-OSA form) |
| Bone mineral density |
Moderate (epidemiological) |
No (animal only for E. arvense) |
| Wound healing (topical) |
Moderate |
Yes |
| Anti-inflammatory |
Low–Moderate |
No |
The evidence base supports cautious, targeted use — particularly for hair/nail brittleness and topical wound support. Bone density benefits are plausible based on silicon's role in collagen metabolism but require more direct human trial evidence before strong recommendations can be made.