The European Journal of Public Health Advance Access published online on January 5, 2007
The European Journal of Public Health, doi:10.1093/eurpub/ckl271
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Medical costs of obese Japanese: a 10-year follow-up study of National Health Insurance in Shiga, Japan
Koshi Nakamura1, Tomonori Okamura1, Hideyuki Kanda2, Takehito Hayakawa3, Akira Okayama4, Hirotsugu Ueshima1 and The Health Promotion Research Committee of the Shiga National Health Insurance Organizations5
1 Department of Health Science, Shiga University of Medical Science, Otsu City, Shiga, Japan
2 Department of Hygiene and Preventive Medicine, Fukushima Medical University, Fukushima City, Fukushima, Japan
3 Department of Public Health Science, Shimane University School of Medicine, Izumo City, Shimane, Japan
4 Department of Preventive Cardiology, National Cardiovascular Center, Suita City, Osaka, Japan
Correspondence: Koshi Nakamura, MD, PhD, Department of Health Science, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu City, Shiga, 520-2192, Japan, tel: +81-77-548-2191; fax: +81-77-543-9732; e-mail: ksnkmr{at}belle.shiga-med.ac.jp
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/m2), participants were classified into the following three categories: BMI < 18.5, 18.5 
BMI < 25.0 and 25.0 BMI. Medical costs per person per month were compared among the three categories. Excess medical costs attributable to the 25.0 BMI category compared to the 18.5 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 BMI < 25.0) and 155 Euros (25.0 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 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.
Keywords: obesity, body mass index, medical costs, Japan