Medical costs of obese Japanese: a 10-year follow-up study of National Health Insurance in Shiga, Japan.

BACKGROUND For the Japanese population, a body mass index (BMI) of 25.0-29.9 is classified as obesity and is a risk factor for cardiovascular disorders such as hypertension. METHODS A cohort study to clarify obesity costs for a Japanese population was conducted utilizing baseline BMI and medical costs over a 10-year follow-up period. The participants were 4502 community dwelling Japanese National Health Insurance (NHI) beneficiaries aged 40-69 years. According to their baseline BMI values (kg/m(2)), participants were classified into the following three categories: BMI < 18.5, 18.5 < or = BMI < 25.0 and 25.0 < or = BMI. Medical costs per person per month were compared among the three categories. Excess medical costs attributable to the 25.0 < or = BMI category compared to the 18.5 < or = BMI < 25.0 category were estimated. RESULTS Approximately 20% of the Japanese population studied had a BMI of 25.0 or over. A J-shaped relationship between BMI and personal total medical costs was observed. Personal total medical costs per month determined from the 10-year follow-up in each category were 189 Euros (BMI < 18.5), 134 Euros (18.5 < or = BMI < 25.0) and 155 Euros (25.0 < or = BMI). A J-shaped pattern was observed after adjusting for age, sex, smoking and drinking habits, and excluding early deceased participants. Furthermore, smoking habit did not modify the J-shaped pattern of total medical costs. The estimated excess medical costs for the 25.0 < or = BMI category represented 3.1% of the total medical costs for the entire study population (634 105 Euros). CONCLUSION The Japanese NHI beneficiaries with a BMI of 25.0 or over showed increased medical costs compared to those with a BMI of 18.5-24.9.