Table 2.

Studies regarding Si supplementation and bone health in humans.

First author, year	Study design	Setting	Inclusion criteria	Exclusion criteria	Intervention	Parallel treatments	Number of subjects (M-F)	Duration of the intervention	Primary outcomes	Secondary outcomes	Results
Eisinger et al. 35	Retrospective study	Free-living subjects	Osteoporosis	/	Si (n = 8)	Placebo (n = 16) Fluoride (n = 10) Etidronate (n = 13) Magnesium (n = 6)	53 osteoporotic women	14–22 months	Vertebral and femoral bone mineral density (BMD) changes	/	Si induced a significant increase in femoral BMD. Fluoride induced a significant increase in vertebral and a slight decrease in femoral BMD. Etidronate and, to a lesser extent, magnesium induced a slight although statistically non-significant increase in vertebral BMD.
Li et al. 36	Randomized, placebo-controlled trial	Free-living subjects	Postmenopausal women within 5 years of menopause; reduced bone density but no evidence of osteoporosis or osteopenia by DEXA scan (T ≥ −1.5 in the total hip and lumbar spine); written informed consent.	Women with a body mass index (BMI) > 30 kg/m2 or who were being treated with estrogens, corticosteroids, or bisphosphonates, who consumed more than one alcoholic beverage a day, or who had significant illness affecting bone metabolism.	1200 mg of calcium + 800 IU of vitamin D + 1 liter of Si-rich artesian aquifer water (SW, 86 mg/L silica)/day	1200 mg of calcium + 800 IU of vitamin D + 1 L of purified water of low-Si content (PW, undetectable amount of silica)/day	17 post-menopausal women (average age 54 years)	12 weeks	Changes in urinary Si level. Changes in serum parathyroid hormone (PTH) level and bone turnover markers (procollagen type I intact N-terminal propeptide, bone specific alkaline phosphatase and osteocalcin). Changes in urinary collagen type 1 cross-linked N-telopeptide (NTx) excretion.	/	The urinary Si for the SW group increased by 133.5%, a statistically significant increase by comparison to the PW group (no change in the urinary Si level). No change of PTH or markers of bone formation including procollagen type I intact, N-terminal propeptide, bone specific alkaline phosphatase, and osteocalcin within groups or between groups. No change in urinary NTx during the study within groups or between groups.
Spector et al. 37	Double-blind randomized placebo controlled trial	St Thomas' Hospital, London	Osteopenic, but otherwise healthy women; written informed consent.	Renal failure as defined by serum creatinine > 200 μmol/L, abnormal serum ferritin level, concomitant medication, oral glucocorticoid treatment, local injectable glucocorticoid treatment if > 5 injections per year, inhaled glucocorticoid treatment if > 6 months in the previous year and more than 2 mg/day prednisone equivalent, concomitant or previous treatment for bone diseases, concomitant and previous use of food supplements containing silicon or horsetail herb extract, bamboo extract, colloidal silicic acid, or silanol derivatives in the previous 6 months	1000 mg Ca and 20 microg cholecalciferol (Vit D3) and three different ch- orthosilicic acid (OSA) doses (3, 6 and 12 mg Si)	A choline-glycerol solution without ch-OSA	184 women (mean age for placebo: 62.0 ± 10.9 (n = 37); mean age for 3 mg Si: 60.4 ± 11.8 (n = 33; mean age for 6 mg Si: 59.7 ± 9.4 (n = 33); mean age for 12 mg Sì: 60.8 ± 9.7 (n = 33))	12 months	Evaluation of the effect of oral choline-stabilized orthosilicic acid and Si on markers of bone turnover and on bone mineral density in osteopenic women	/	There were no significant changes in femoral and lumbar BMD following the intake of ch-OSA; however, a post hoc analysis of subgroup of the femoral neck BMD (subjects with baseline femoral T-score <−1) showed a significant change of this parameter in the group treated with 6 mg of Si compared to the placebo group (BMD total femur and femoral neck greater than 0.98% and 2% respectively), with possible consequent reduction in the risk of hip fractures.
Spector et al. 35	Double-blind randomized placebo controlled trial	St Thomas' Hospital, London	Osteopenic, but otherwise healthy women; written informed consent.	Renal failure as defined by serum creatinine > 200 μmol/L, abnormal serum ferritin level, concomitant medication, oral glucocorticoid treatment, local injectable glucocorticoid treatment if > 5 injections per year, inhaled glucocorticoid treatment if > 6 months in the previous year and more than 2 mg/day prednisone equivalent, concomitant or previous treatment for bone diseases, concomitant and previous use of food supplements containing silicon or horsetail herb extract, bamboo extract, colloidal silicic acid, or silanol derivatives in the previous 6 months	Three different ch-OSA doses (3, 6, and 12 drops) were used corresponding to 3, 6, and 12 mg Si. All subjects received calcium and vitamin D3 (1000 mg calcium and 20 mg cholecalciferol) daily	A choline-glycerol solution without ch-OSA	114 women (average age: 61 years)	12 months	Investigate the effect of low dose oral silicon as an adjunct to calcium/vitamin D3 on markers of bone turnover and BMD.	/	The doses of 6 and 12 mg of Si were also shown to be significantly associated with an increase in procollagen type I N propeptide, while no significant change in BMD to the column was observed