The Impact of Obesity Duration on Healthcare Use

A considerable volume of research has demonstrated differences in health, mortality rates, and healthcare use across various categories of body mass index (BMI)—with the obese (BMI>29.9) showing worse health and higher health care use, and, in some cases, higher mortality rates. However, these analyses generally do not consider the length of time an individual was obese, despite significant variation in this duration. Evidence from the literature indicates that a longer duration of obesity, conditional upon current weight, is associated with increased risks for coronary artery disease, type II diabetes, and death. Because childhood obesity rates roughly doubled from 1980 to 2010, individuals from more recent cohorts are projected to be obese for longer periods of time, on average. This increased average duration could lead to substantial cross-cohort differences in the rates of obesity-related disease and healthcare costs.

We examine the relationships between the duration of obesity and (i) healthcare utilization and (ii) obesity-related chronic conditions. We use six waves of the National Health and Nutrition Examination Survey to analyze trends in obesity duration, using self-reported measures of BMI ten years prior to the survey and at age 25 to infer the duration of obesity. These measures are used to estimate whether those who are obese for longer periods of time, controlling for their current obesity status, use more healthcare services and are more likely to be hospitalized. We also explore whether longer obesity duration is associated with higher rates of obesity-related disease (including diabetes, heart disease, and arthritis) and lower levels of physical functioning.

Preliminary results confirm the substantial increase in obesity rates, particularly in early adulthood, documented elsewhere. Obesity rates at age 25 increased from 4 percent for the 1940-1944 birth cohort to 19 percent for the 1980-1984 birth cohort. This early onset of obesity is related to later life healthcare utilization. Among those ages 45 and above, those not obese at age 25 but currently obese were 23 percent (3 percentage points) more likely to be hospitalized in the past year compared with those with a BMI less than 30. However, those currently obese who were obese at 25 were 43 percent (6 percentage points) more likely to be hospitalized. Obesity at age 25 similarly increased the likelihood that an individual had 8 or more healthcare visits in the past year, conditional on current BMI level.

This research has implications for projections of the future costs obesity. If the duration of obesity is related to these costs and younger cohorts will be obese for a longer portion of their life, then past research may inaccurately predict the future effects of obesity on health and health care costs. Further, this study has implications for the theoretical benefits of obesity interventions. If a longer duration of obesity is more costly or detrimental to health, then, other effects equal, there may be added benefits to interventions that decrease this duration, perhaps by focusing on childhood obesity.