The Effect of Dietary Vitamin D3 Level on Bone Osteometry and Mechanical Properties in Young Rats

Abstract

Recent knowledge indicates that vitamin D3 not only regulates the calcium-phosphate metabolism, but also as a hormone with steroidal features, has significant remedial-homeostatic ability and has a pleiotropic function in the body. Medical observations confirm the beneficial effect of elevated levels of vitamin D3 in the prevention or alleviation of the course of many diseases of the cancer and autoimmune basis, diabetes and coronary diseases. The deficiencies of this vitamin in children, adolescents and young women are observed, causing the rickets or bone fragility. As the increasingly limited role of obtaining vitamin D3 from the sun exposure, supplementation of food sources becomes particularly important. The aim of the study was to evaluate the effect of the increased dietary vitamin D3 level on health status using rats as the model animals. The experiment was carried out on 36 weaned rat Wistar, half female and male, 5–6 weeks old. Animals were divided into 3 groups. All rats obtained ad libitum the same feed mixture but differed in the vitamin D3 level (0, 1000 or 5000 IU/kg). Bone length and weight, cross-section area and wall thickness were measured, cortical index was calculated. The mechanical properties were determined using the 3-point bending test performed on a universal testing machine (Zwick Z010). The supports were placed at 40% of the total bone length and the measuring head loaded bone samples with a constant speed of 10 mm/min until fracture. The bone mineral density was determined using the dual-energy X-ray absorptiometry (DEXA) method on a DiscoveryWHologic X-ray densitometer. We observed that, the vitamin D3 presence in feed did not significantly affect the bone geometrical traits in young rats. The vitamin D3 supplementation, regardless its level, increased the bone mineral density by 8–12% (P<0.05) and some mechanical properties were improved (P<0.05) in comparison to group without vitamin D3 supplementation. Also, the femur bone of rats supplemented with vitamin D3 characterised by the higher share force (11–14%), work needed for destruction (24–55%), ultimate strain, ultimate stress (5–7%). The bone elastic strength was the highest in group III, receiving the vitamin D3 in amount excessing the standard requirement of rats. Summerizing it can be concluded, contrary to the assumptions, we did not confirmed the significant effect of increased vitamin D3 level in feed on MBD and most of the mechanical traits. However, the maximal elastic strenght was the highest in group receiving 5000 IU/kg of vitamin D3, which reflects the highest elastic strength of midshaft cortical bone under reversible deformation and the maximum stress which a bone can withstand before fracture, but the difference was not statistically confirmed.