 Primary endpoint: Urinary N-telopeptide of type I collagen NTXCr. Secondary endpoints: other bone turnover markers, BMD, muscle function, thyroid function, blood glucose, anti-oxidant activity, inflammatory markers The investigators will make the primary analysis based on women with baseline serum selenium below 120 mcgl. To ensure adequate power for this analysis we will plan to recruit 120 women we expect that 100 of the 120 will have serum selenium below 120 mcgl based on our previous cross-sectional study. The investigators will review the baseline serum selenium results when 40 women have been recruited to confirm the expected distribution of baseline levels, and we will adjust the total recruitment number accordingly to ensure at least 99 women with serum selenium below 120mcgl have been randomised for the final primary endpoint intention-to-treat analysis. 