Kidney Function and Rate of Bone Loss at the Hip and Spine: The Canadian Multicentre Osteoporosis Study

Background: The relationship between kidney function and bone loss is unclear. Study Design: A prospective observational study. Setting & Participants: 191 men and 444 women aged ≥ 50 years participating in a population-based observational study designed to determine risk factors for bone loss and fractures. Predictors: The primary predictor of change in bone mineral density (BMD) was estimated creatinine clearance (using the Cockcroft-Gault formula) measured at baseline and stratified by quartiles. Our secondary predictor was estimated glomerular filtration rate using the Modification of Diet in Renal Disease Study equation, also stratified by quartiles. Outcomes & Measurements: Changes in BMD at the lumbar spine, total hip, and femoral neck during 5 years. Results: Compared with participants in the first quartile of estimated creatinine clearance (>101.2 mL/min), those in remaining quartiles were older (quartile 1, 50.0 years; quartile 2 [101.2-83.4 mL/min], 54.7 years; quartile 3 [83.4-68.3 mL/min], 60.5 years; and quartile 4 [<68.3 mL/min], 68.3 years); weighed less; reported more sedentary hours; were less likely to report excellent, very good, or good self-reported health; consumed less caffeine; and had lower serum calcium and phosphate and higher serum parathyroid hormone levels. After adjusting for age, weight, sex, baseline BMD, and these differences, compared with those in the first quartile, those in the fourth quartile had decreases in BMD of 0.08 g/cm² (95% CI, 0.04-0.1) at the lumbar spine, 0.08 g/cm² (95% CI, 0.06-0.1) at the femoral neck, and 0.09 g/cm² (95% CI, 0.07-0.1) at the total hip. Bone loss did not increase with worsening kidney function (P for trend > 0.05). Results were not substantially different using estimated glomerular filtration rate. Limitations: Observational study design and indirect measures of kidney function. Conclusions: Men and women with impaired kidney function are at increased risk of bone loss, even with minimal reduction in kidney function.