Mobility Limitation and Body Mass Index: Identifying Impact and Environmental Moderating Effects

Obesity is more prevalent among people with mobility limitations than those without. Having a mobility limitation is associated with obesity in cross-sectional studies but the role of mobility limitations in causing increases in weight is unclear. The direction of this relationship is important for informing how public health policy and interventions should address the high rate of obesity among people with mobility limitations. It is also important to understand what personal and environmental factors might moderate this relationship. Unfortunately there are few longitudinal surveys available for studying mobility limitation in adults over time. Healthcare administrative data provide new opportunities for research but there are challenges to using such data to study people with mobility limitations. The overall purpose of this dissertation was to better understand the effect of a mobility limitation on BMI and how that effect is modified in the context of personal and environmental factors. The first chapter of this dissertation is a study about the development of a predictive algorithm to identify people with mobility limitations using healthcare administrative data. I linked healthcare administrative data to self-reported mobility limitation and tested different predictive models. I found that a multilevel mobility limitation approach did not work well but a binary mobility limitation algorithm had good sensitivity and specificity. I used the algorithm in chapters two and three to study people with mobility limitation in a large, national cohort of veterans from the Weight and Veterans Environment Study. Chapter two was a longitudinal study to tease out the effects of a mobility limitation on BMI. I used fixed effects regression models that address important threats to causal interpretation of the findings. I found that having a mobility limitation increased BMI but by a smaller magnitude than previously reported. There were larger effects among younger aged veterans and those with many comorbidities. In the third chapter, I examined the role of the neighborhood environment as a moderator of the relationship between mobility limitation and BMI among a national sample of veterans. I found that the higher the level of neighborhood walkability, the smaller the effect of mobility limitation on BMI. Additionally, being in a high poverty and low walkability neighborhood was associated with a higher increase in BMI as a result of a mobility limitation. The findings from this dissertation have implications for public health research, practice, and policy.