The comparative absorption of silicon from different foods and food supplements

Abstract

Dietary Si (orthosilicic acid; OSA) appears important in connective tissue health, and although the sources and intakes of Si are well established, its absorption is not. Si absorption was measured from eight high-Si-containing sources: alcohol-free beer; OSA solution (positive control); bananas; green beans; supplemental choline-stabilised OSA (ChOSA); supplemental monomethyl silanetriol (MMST); supplemental colloidal silica (CS); magnesium trisilicate British Pharmacopoeia antacid (MTBP). Two of the supplements and the antacid were pre-selected following an in vitro dissolution assay. Fasting, healthy subjects (CS, n 3; others, n > or = 5) each ingested two of the sources separated by a 1-week wash-out period. Blood and urine were collected and measured for total Si concentrations by inductively coupled plasma optical emission spectrometry. Absorption, based on urinary Si excretion, was highest for MMST and alcohol-free beer (64% of dose), followed by green beans (44%), OSA (43%), ChOSA (17%), bananas and MTBP (4%) and CS (1%). Peak serum concentrations occurred by 0.5 h for MMST and green beans, 1.5 h for OSA and alcohol-free beer, 2 h for ChOSA and CS, and 4 h for MTBP. Area under the serum curves correlated positively with urinary Si output (r 0.82; P < 0.0001). Absorption of Si from supplements and antacids was consistent with their known chemical speciation and kinetics of dissolution under simulated gastrointestinal conditions. Monomeric silicates were readily absorbed, while particulate silicates were decreasingly well absorbed with increasing polymerisation. The present results highlight the need to allow for relative absorption of Si from different foods or supplements in subsequent epidemiological and intervention studies.

Fig. 1

Dissolution (mg Si/g product) of Si from different Si-containing products and supplements under simulated gastrointestinal (SGI) conditions at timed intervals following neutralisation of SGI fluid (SGIF) from gastric to intestinal pH. (), Silica complex; (■), horsetail; (□), colloidal silica; (), magnesium trisilicate British Pharmacopoeia; (), choline-stabilised orthosilicic acid (BioSil; BioMinerals NV, Destelgergen, Belgium). Results are means of three samples, with standard errors represented by vertical bars. *Mean value was significantly different from that at baseline (i.e. 0 min) (P<0·01; repeated-measures ANOVA).

Fig. 2

Serum Si (μg/l) over the 6 h period following the ingestion of: (a) an orthosilicic acid (OSA) solution containing 21·4 mg Si (–○–; n 5) and alcohol-free beer containing 22·9 mg Si (–●–; n 5); (b) cooked green beans containing 6·1 mg Si (–△–; n 5) and ripe, peeled bananas containing 13·6 mg Si (–▲–; n 5); (c) colloidal silica containing 780 mg Si (–□–; n 3) and magnesium trisilicate British Pharmacopoeia (BP) containing 200 mg Si (–■–; n 8); (d) choline-stabilised orthosilicic acid (ChOSA) containing 20 mg Si (–◆–; n 8) and monomethyl silanetriol (MMST) containing 6·9 mg Si (–◇–; n 14). Results are means, with standard errors represented by vertical bars. To allow for optimal clarity of figures with respect to graphical overlap, each of (c) and (d) show one set of data from study 3 and from study 4; i.e. magnesium trisilicate BP (shown in (c)) was ingested in study 3 with ChOSA (shown in (d)), while colloidal silica (shown in (c)) was ingested in study 4 with MMST (shown in (d)). Si-containing supplements and products were ingested at the maximum dose recommended. The increase in serum Si following the ingestion of alcohol-free beer, OSA, magnesium trisilicate BP, ChOSA and MMST was statistically significant (all P<0·0001), as it was for colloidal silica (P<0·001) and green beans (P=0·04), but not for bananas (P=0·43).

Fig. 3

Urinary Si excretion (mg/3 h) over the 6 period following the ingestion of: (a) an orthosilicic acid (OSA) solution containing 21·4 mg Si (n 5); (b) alcohol-free beer containing 22·9 mg Si (n 5); (c) cooked green beans containing 6·1 mg Si (n 5); (d) ripe, peeled bananas containing 13·6 mg Si (n 5); (e) colloidal silica containing 780 mg Si (n 3); (f) magnesium trisilicate British Pharmacopoeia (BP) containing 200 mg Si (n 8); (g) choline-stabilised orthosilicic acid (ChOSA) containing 20 mg Si (n 8); (h) monomethyl silanetriol (MMST) containing 6·9 mg Si (n 14). Results are means, with standard errors represented by vertical bars (n 5-14, see Table 1). Si-containing supplements and products were ingested at the maximum dose recommended. The increase in urinary Si excretion (0-6 h) was statistically significant following the ingestion of OSA (P<0·0001), alcohol-free beer (P<0·001), green beans (P=0·04), magnesium trisilicate BP (P<0·001), ChOSA (P<0·001), MMST (P<0·001) and colloidal silica (P=0·03), but not following the ingestion of bananas (P=0·13).

Fig. 4

Percentage increase in excretion of urinary Si over the 6 h period following the ingestion of: an orthosilicic acid (OSA) solution containing 21·4 mg Si (n 5); alcohol-free beer containing 22·9 mg Si (n 5); cooked green beans containing 6·1 mg Si (n 5); ripe, peeled bananas containing 13·6 mg Si (n 5); colloidal silica containing 780 mg Si (n 3); magnesium trisilicate British Pharmacopoeia (BP) containing 200 mg Si (n 8); choline-stabilised orthosilicic acid (ChOSA) containing 20 mg Si (n 8); monomethyl silanetriol (MMST) containing 6·9 mg Si (n 14). Results are means, with standard errors represented by vertical bars. Si-containing supplements and products were ingested at the maximum dose recommended.

Fig. 5

Correlation (r 0·82, P<0·0001; n 48) between area under the curve (AUC; 0-6 h) of serum Si (mg × h/l) and the increase in urinary Si excretion following the ingestion of the different Si sources over the 6 h study period: orthosilicic acid (○; n 5); alcohol-free beer (●; n 5); cooked green beans (△; n 5); ripe, peeled bananas (▲; n 5); colloidal silica (□; n 3); magnesium trisilicate British Pharmacopoeia (■; n 8); monomethyl silanetriol (◇; n 9); choline-stabilised orthosilicic acid (◆; n 8).