Dietary silicon intake and bioavailability - Bone Health - Brief Article

Nutrition Research Newsletter, June, 2002

Increasing evidence suggests that silicon plays a major role in bone formation, yet the bio-availability of silicon from the diet is unclear. It is assumed that silicon is available only from fluids, such as water and beer, but not from solid foods. However, because fluids account for only 20 to 30% of total silicon intake and because silica in solid foods could be hydrolyzed in the gastrointestinal (GI) tract, further research is needed on the bioavailability of silicon.

The kidney is the major route of excretion of absorbed silicon. Therefore, urinary silicon is a good proxy for absorption. The authors used urinary silicon as a measure of silicon uptake from the GI tract. The current study is set out to determine the intake and GI uptake of dietary silicon in adults and whether the silicon content of foods can be used as a marker for its uptake.

The subjects in the study of silicon intake were members of the Framingham study and the Framingham Offspring Study. Usual dietary intakes of the subjects were determined with the use of a semi-quantitative, 126-item food-frequency questionnaire. In the second part of the study, three to eight healthy subjects were used. The subjects fasted overnight and then continued to fast until 6 hours after ingestion of the test meal. Throughout this period, subjects ingested ultra-high purity water with negligible silicon content. GI uptake of silicon from foods was then estimated by using urinary silicon excretion as a surrogate measure of silicon uptake.

Total dietary intakes of silicon were between 13 and 62 mg/day, similar to previously reported values of 20 to 50 mg/ day from ester diets. Silicon intakes in men were significantly higher than those in women. Silicon intake also decreased with age. The major food sources were beer and bananas and string beans in women. The second part of the study showed that a mean of 41% of the ingested silicon was excreted in the urine or that silicon was readily available from foods. The silicon content of foods consumed was significantly correlated with urinary silicon excretion.

In conclusion, foods are major sources of available silicon for humans. The higher silicon intake in men can be explained by higher beer consumption in young men, which accounted for 45% of their total silicon intake. Since a significant correlation was found between silicon intake and urinary silicon excretion, it can be assumed that silicon contents of foods can be used to estimate exposure in future epidemiologic studies. This should allow researchers to examine the effect of dietary silicon on bone health.

Ravin Jugdaohsingh, Simon HC Anderson, Katherine L Tucker, et al., Dietary silicon intake and absorption, Am J Clin Nutr, 75:887-893 (May 2002) [Address reprint requests to R dugdaohsingh, Gastrointestinal Laboratory, The Rayne Institute, St Thomas' Hospital, London, Se1 7EH, United Kingdom. E-mail: ravin.jugdaohsingh@kcl.ac.uk]