Dietary silicon intake in Belgium: Sources, availability from foods, and human serum levels

The dietary intake of silicon by using the duplicate portion sampling technique of 24 hour-meals during 7 consecutive days is estimated.Since plant-based foods are major sources of silicon the elemental content is determined in various vegetarian foodstuffs commercially available in Belgium.Mean silicon intake from the 24-hour duplicate meals consumed daily by nearly 2000 persons was 18.6 +/- 8.5 mg/day. The major food sources were unrefined grains of high fibre content, cereal products and root vegetables. For vegetarian foods rice and barley revealed high silicon levels. Very high serum concentrations in newborns and concomittant low levels in the mothers indicated a homeostatic mechanism in humans. Besides the dietary intake, serum silicon levels of various population groups support the concept of essentiality of the element. An in vitro dialysability of the element in a simulated digestion procedure is used as a surrogate of silicon uptake.Silicon was readily available from foods but this correlated inversely with the elemental content.Serum silicon levels, as a function of age, gave indication of an important role of this element. In vitro availability study proved an inverse relation with the elemental content. A preliminary in vivo experiment confirmed that bioavailability is not only determined by concentration, but especially by the type of food and species under which silicon is present.