An investigation into the effects of Omega-3 fatty acids on bone resorption in the female ovariectomised rat : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Nutritional Science at Massey University

Abstract

Estrogen deficiency results in disruption of the normal bone remodeling cyclc leading to a loss of bone mineral and, in many cases, the development of osteoporosis. Various studies have demonstrated a beneficial effect of essential fatty acids (EFAs) in reducing the loss of bone density as a consequence of estrogen deficiency. The aim of the present study was to examine the specific effects of the n-3 EFA, eicosopentaenoic acid (EPA) on bone density and strength in ovariectomised female rats. 60 Sprague-Dawley rats were randomized into four groups and either ovariectomised (n=45) or sham operated (n=15). Ovariectomised animals were fed calcium adequate diets containing either corn oil (OVX control, n=15), corn oil + 0.1g/kg body weight EPA (low dose, n=15) or corn oil + 1.0g/kg body weight EPA (high dose, n= 15) for a period of nine weeks. Sham rats were fed the corn oil diet as per the OVX control group. Urinary calcium and phosphate excretion, serum type 1 collagen c-telopeptide concentration, bone density, bone ash and bone breaking strength were measured. Plasma fatty acid composition and serum concentrations of 25 hydroxyvitamin D3 were also determined. Femur bone density was significantly lower in the high dose group compared to sham, OVX control and low dose EPA groups (p<0.001, p=0.0096 and p=0.0047 respectively). Low dose EPA supplementation had no significant effect on bone density. No significant differences in urinary calcium or phosphate concentrations, serum concentrations of type-1 collagen c-telopeptide or bone breaking strength were evident with either dose of EPA compared to unsupplemented, ovariectomised controls. EPA supplementation resulted in significant decreases in the levels of n-6 EFAs and increases in the levels of n-3 EFAs except docosahexaenoic acid in plasma lipids. Both low and high dose EPA supplementation led to significant increases in serum concentration of25(OH) vitamin D3. In conclusion 1.0g EPA/kg body weight had a detrimental effect on bone density in ovariectomised rats. It is proposed that high intake of the highly unsaturated EPA resulted in significant lipid peroxidation. This in turn disrupted membrane structure and inhibited intestinal calcium absorption thereby stimulating PTH-mediated bone resorption. potential role for n-3 EFAs in the regulation of vitamin D activity is also outlined