To evaluate the independent and joint effects of C-reactive protein (CRP) and 25-OH vitamin D (25(OH)D) levels on mobility disability in older persons.DESIGN:
U.S. population-based cross-sectional study.SETTING:
National Health and Nutrition Examination Surveys (2001–2002).PARTICIPANTS:
Individuals aged 50 and older (N = 1,826).MEASUREMENTS:
C-reactive protein (mg/dL), with high CRP defined as ≥0.2 mg/dL, and 25(OH)D levels (ng/mL) operationalized as severe deficiency (<10 ng/mL), deficiency (10–19.9 ng/mL), insufficiency (20–29.9 ng/mL), and normal (≥30 ng/mL). Mobility disability was operationalized as gait speed of <0.8 m/s while completing a 20-foot walk (6.1 m).RESULTS:
High CRP and low 25(OH)D levels were associated with slow gait speed. Individuals with high CRP levels and severe vitamin D deficiency were more likely to have slow gait speed than were those with neither risk factor (odds ratio = 3.54, 95% confidence interval = 1.42–8.84, P = .007). A significant positive association between vitamin D level and gait speed was found only in those with high CRP in stratified analyses. Whites and blacks showed similar findings as the overall population.CONCLUSION:
These findings provide evidence of a potential joint effect of vitamin D and CRP on gait speed, suggesting that evaluation and correction of vitamin D levels may be especially important in individuals with high CRP levels. J Am Geriatr Soc 61:1574–1579, 2013.