Is there a biomedical explanation for socioeconomic differences in incident mobility limitation?

Background. The association between low socioeconomic status and poor physical functioning has been well described; biomedical factors may play an important role in explaining these differences. This study examines the association between socioeconomic status and incident mobility limitation in well-functioning older adults, and seeks to determine whether this link could be explained by biomedical factors. Methods. Data were obtained from 3066 men and women, aged 70-79 years from Pittsburgh, Pennsylvania and Memphis, Tennessee participating in the Health, Aging and Body Composition (Health ABC) study. Three indicators of socioeconomic status were used: education, income, and ownership of financial assets. Mobility limitation was defined as reporting difficulty walking 1/4 mile or climbing 10 steps during two consecutive semiannual assessments over 4.5 years. Biomedical factors included a wide range of diseases (e.g., heart and cerebrovascular disease) and biological risk factors (e.g. hypertension, poor pulmonary function, and high serum levels of inflammatory markers). Results. Adjusted hazard ratios of incident mobility limitation were significantly higher in those persons with low education, low income, and few assets. Hazard ratios ranged from 1.66 to 2.80 in the lowest socioeconomic groups. Additional adjustment for biomedical factors reduced the hazard ratios by an average of 41% for education, 17% for income, and 29% for assets. Conclusion. Biomedical factors can account for some of the association between socioeconomic status and incident mobility limitation. However, to reduce physical disabilities and, in particular, the socioeconomic differences therein, it may not be sufficient to solely intervene upon biological risk factors and risks of diseases.