Renal function and bone mineral density in community-dwelling elderly Japanese men: The Fujiwara-kyo Osteoporosis Risk in Men (FORMEN) Study

End-stage renal failure deteriorates bone mass and increases fracture risk. However, there are conflicting reports in the literature regarding the effects of mild to moderate renal dysfunction on bone mineral density (BMD). We investigated the association between renal function and BMD at the spine and hip and bone metabolism markers in community-dwelling elderly Japanese men. From 2174 male volunteers aged ≥ 65 years, we examined 1477 men after excluding those with diseases or medications known to affect bone metabolism. Renal function was assessed by serum cystatin C and estimated glomerular filtration rate (eGFR) calculated using the Modification of Diet in Renal Disease Study equation. Bone metabolism was evaluated using levels of serum amino-terminal propeptide of type I procollagen (PINP) and tartrate-resistant acid phosphatase isoenzyme 5b (TRACP-5b), which represent bone metabolic status independent of renal function. eGFR was inversely associated with BMD after adjusting for potential confounders (P < 0.01). Cystatin C showed a weaker but significant association with BMD. eGFR was modestly positively associated with PINP levels (P = 0.04), although cystatin C concentrations were neither associated with PINP nor TRACP-5b levels. Since BMD integrates bone metabolism from the past to present, inverse associations between renal function and BMD may be attributed to past factors, such as obesity. Our findings suggest that low renal function does not affect bone metabolism in a population of community-dwelling elderly Japanese men. Longitudinal studies will be necessary to clarify whether low renal function affects bone loss.