|Nielsen, Forrest - Frosty|
Submitted to: Bone
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/22/2008
Publication Date: 8/15/2008
Publication URL: http://handle.nal.usda.gov/10113/20792
Citation: Jugdaohsingh, R., Calomme, M.R., Robinson, K., Nielsen, F.H., Anderson, S., D'Haese, P., Geusen, P., Loveridge, N., Thompson, R., Powell, J.J. 2008. Increased longitudinal growth in rats on a silicon-depleted diet. Bone. 43(3):596-606. Interpretive Summary: Humans ingest between 20 and 50 mg of silicon per day in the Western world. This intake is higher than all other trace elements such as iron and zinc. Silicon is efficiently absorbed and excreted so that body concentrations are kept relatively constant. Some recent studies with human cells with bone forming characteristics have indicated that silicon may be beneficial for bone formation. Thus, silicon may have an important role in human health. Studies with rats and chickens in the 1970s support the suggestion that silicon is beneficial, if not essential, for bone and connective tissue health. These studies, however, did not clearly show that high intakes of silicon were preventing a silicon deficiency instead of merely overcoming by pharmacological means some other dietary deficiency or environmental stressor. Thus, an experiment was performed to determine whether silicon deprivation adversely affects growth and development, especially skeletal development, in weanling female rats. Rats were fed a well-balanced diet that provided very low amounts of silicon (0.17 mg/kg body weight per day) and compared to rats fed the same diet with water containing silicon (providing 4.08 mg/kg body weight per day) for 26 weeks. This experiment did not show the marked changes in bone and connective tissue found in the experiments performed in the 1970s. The experiment did not provide any substantial evidence indicating the silicon is an essential nutrient for normal growth and development. It did show that silicon status affected bone length, bone growth plate thickness, and connective tissue cell (chondrocyte) density. Thus, although silicon may not be essential, it apparently does have a beneficial effect on bone and connective tissue. This may be the reason that epidemiological studies have shown that higher intakes of silicon are associated with increased bone mineral density in humans.
Technical Abstract: Background: Silicon-deficiency in growing animals was originally reported to have profound effects on growth and development, notably on connective tissues. However, more recent attempts to replicate these findings have found mild alterations in bone metabolism without any adverse health effects. Thus the biological role of silicon remains unknown. Objective: Using a specifically formulated silicon-depleted diet and modern methods for silicon analysis and assessment of skeletal development, we undertook, through international collaboration between silicon researchers, the most extensive study of long-term silicon depletion on skeletal development in an animal. Design: 21-day old Sprague-Dawley rats were fed a silicon-depleted diet (n=20) for 26 weeks (3.2 ± 0.6 µg Si/g feed) and their growth and skeletal development compared with identical rats (n=10) on the diet but with silicon (as Si(OH)4) added to their drinking water (53.2 µg Si/g water); total silicon intake differed by 24-fold. A third group of rats receiving standard rodent chow and tap water, served as a reference group. A series of anthropometric and bone quality measures were undertaken during and following the study. Results: Fasting serum silicon concentrations and especially urinary silicon excretion were significantly lower in the silicon-deprived group compared to the supplemented group (P = 0.03 and 0.004, respectively). Tibia and soft-tissue silicon contents did not differ. Outward adverse health effects were not observed in the silicon-deprived group, however, body lengths from week 18 onwards (P < 0.05) and bone lengths at necropsy (P </= 0.002) were longer in this group. Moreover, these measures correlated with serum silicon concentrations (P </= 0.02). A reduction in bone growth plate thickness and an apparent increase in chondrocyte density were also observed in the silicon-deprived animals. No other differences were observed between the two groups, except for tibia phosphorus concentrations, which were lower in the silicon-deprived animals (P = 0.0003). Conclusion: We were unable to reproduce the profound deficiency state reported in rats and chicks in the early 1970’s, but we identified three areas that require further consideration in relation to silicon depletion; (i) delayed maturation of the longitudinal growth plate in relation to low circulating silicon concentrations (here demonstrated), (ii) bone quality in relation to bone-silicon concentrations (unchanged here) and (iii) homeostasis of silicon through renal conservation (implied here).