High bone turnover in the elderly

Objectives: To document lifestyle-associated variations in biochemical mark ers of bone metabolism in advanced age. Study Design: Cross-sectional study. Setting: Department of Geriatrics, University Hospital, Basel, Switzerland. Subjects: Three hundred twelve ambulatory and 193 institutionalized men and women, aged 54 to 99yrs. Outcome Measurements: Biochemical markers of bone resorption (urinary deoxy pyridinolin and N-telopeptides), serum vitamin D metabolites, and serum int act parathyroid hormone (iPTH) concentrations were assessed. Mean values of all parameters were correlated with a six-grade activity score. Physical a ctivity score reflected the degree of weight bearing, ranging from walking independently to primarily bed-bound. Ambulatory subjects were measured in summertime and institutionalized subjects in wintertime to accentuate seaso nality of vitamin D hormone levels. Results: Excretion of bone resorption markers was significantly higher in t he institutionalized and physically inactive patients compared with those w ho were ambulatory and physically active (p =.0001). Vitamin D deficiency ( 25-hydroxyvitamin D of <12ng/mL) was present in 86% of institutionalized an d 15% of ambulatory subjects, and 1,25-dihydroxyvitamin D serum concentrati ons were lower in institutionalized than in ambulatory subjects (p =.0001). Mean serum concentrations for iPTH were similar for both the institutional ized and ambulatory groups. When subjects were arranged according to activi ty score, mean excretion of urinary bone resorption markers increased with degree of inactivity. Conclusion: Despite the difference in vitamin D metabolites, iPTH serum con centrations did not differ significantly between the institutionalized and ambulatory groups. However, institutionalized and physically inactive parti cipants had markedly elevated excretion of urinary bone resorption markers compared with ambulatory and physically active subjects. These results sugg est that high bone turnover in the elderly may be caused by physical inacti vity related to low mechanical loading rather than secondary hyperparathyro idism. (C) 1999 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.