Body mass index and medical care costs among Japanese adults

INTRODUCTION: Obesity confers an increased risk of cardiovascular diseases, diabetes, and hypertension, and consequently increases health care expenditure. In addition, social, environmental, and economic factors influence individual health care costs. This study aimed to identify the association between body mass index (BMI) and health care costs, after controlling for social and environmental factors, among Japanese adults aged 20 years and above.

METHODS: The data were obtained from Japan Household Panel Survey, which was conducted between 2009 and 2011 using structured questionnaire. In total, 2066 participants were followed for 3 years and included in analysis. Annual out-of-pocket expenditure on health care was the outcome variable. Sex, equivalent income, occupation, education, residence, physical and psychological status, smoking habit, alcohol consumption, and payment for health promotion activities were controlled. However, several values of the outcome variable were outliers, which necessitated the application of robust and quantile regression models to examine the association between BMI and health care costs according to age (20–39 years, 40–59 years, 60–69 years, and 70 years and above). 

RESULTS: The proportions of overweight (BMI=18.5–24.9) and obese (BMI >30.0) individuals were 17.8% and 3.5%, respectively. The robust regression model showed that one unit BMI was increased 6.7 USD annual health care costs, but only in individuals aged 40–59 years (p = 0.003). In the quantile regression model, the 75 percentiles of annual health care costs of obesity individuals paid 820 USD and overweight person paid 200 USD higher than normal weight individuals in age between 40 and 59 years. 

CONCLUSIONS: A higher BMI increases the expenditure on health care; however, this association is influenced by age. Weight control programs should be organized particularly for middle-aged populations.