Objectives: To document lifestyle-associated variations in biochemical markers 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 99 yrs.
Outcome measurements: Biochemical markers of bone resorption (urinary deoxypyridinolin and N-telopeptides), serum vitamin D metabolites, and serum intact parathyroid hormone (iPTH) concentrations were assessed. Mean values of all parameters were correlated with a six-grade activity score. Physical activity 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 seasonality of vitamin D hormone levels.
Results: Excretion of bone resorption markers was significantly higher in the institutionalized and physically inactive patients compared with those who were ambulatory and physically active (p = .0001). Vitamin D deficiency (25-hydroxyvitamin D of <12 ng/mL) was present in 86% of institutionalized and 15% of ambulatory subjects, and 1,25-dihydroxyvitamin D serum concentrations were lower in institutionalized than in ambulatory subjects (p = .0001). Mean serum concentrations for iPTH were similar for both the institutionalized and ambulatory groups. When subjects were arranged according to activity score, mean excretion of urinary bone resorption markers increased with degree of inactivity.
Conclusion: Despite the difference in vitamin D metabolites, iPTH serum concentrations did not differ significantly between the institutionalized and ambulatory groups. However, institutionalized and physically inactive participants had markedly elevated excretion of urinary bone resorption markers compared with ambulatory and physically active subjects. These results suggest that high bone turnover in the elderly may be caused by physical inactivity related to low mechanical loading rather than secondary hyperparathyroidism.