Cystatin C and Objectively Measured Mobility 10 Years Later in Older Women.

BACKGROUND: Serum biomarkers predicting physical performance in late life are uncertain. We tested the hypotheses that lower serum cystatin C (cysC) in older women is associated with good mobility 10 years later. METHODS: We conducted a longitudinal analysis of a prospective cohort of 1,384 women attending Year 10 and Year 20 examinations of the Study of Osteoporotic Fractures. Serum cysC was measured using Year 10 frozen serum specimens. Year 20 mobility was ascertained by the Short Physical Performance Battery; scores of 10-12 indicated good mobility. RESULTS: At Year 20, mean age was 87.5 years and 364 women (26.3%) had good mobility. After adjustment for age, race, education, health status, diabetes, cardiovascular disease, and body mass index, lower cysC at Year 10 was associated with a higher likelihood of good mobility at Year 20. Compared with quartile (Q) 4 of cysC (referent group), odds ratios (95% confidence interval) were 1.52 (1.02-2.25) for Q3, 1.93 (1.32-2.84) for Q2 and 1.80 (1.21-2.67) for Q1 (p trend across Qs .003). The association was only modestly attenuated after further adjustment for mobility as assessed by a modified Short Physical Performance Battery at Year 10 (p trend .02) or consideration of potential biologic mediators including Year 10 levels of serum 25-hydroxyvitamin D, interleukin 6, and cytokine soluble receptors (p trend .04). CONCLUSIONS: Lower cysC in older women is independently associated with good mobility 10 years later and may be a biomarker for successful aging as manifested by preservation of lower extremity performance in late life.