Impact of high body mass index on health state utilities: a time trade-off study in the general population of Japan.

AIMS: Given the increasing burden of patients with obesity disease, the impact of weight loss on health state utility needs to be reflected in cost-effectiveness analyses of new treatments. Equally important is that, health state utilities that reflect the preferences of the general population are of value for cost-effectiveness analyses. The aim of this time trade-off (TTO) study in the general population of Japan is to estimate the health state utilities of patients with obesity disease.

METHODS

Vignettes were generated for health states categorized by BMI (kg/m2), as follows: ≥25 to <30, ≥30 to <35, ≥25 to <35, or ≥35. The vignettes were validated by a medical expert and patients with obesity disease. A pilot survey examined the general population's comprehension of the vignettes before the main survey. Face-to-face interviews were conducted with the general population in both the pilot and main surveys by trained interviewers. Respondents were asked to imagine themselves in each vignette. Health state utilities were measured for each vignette using the TTO method.

RESULTS

The main survey and pilot survey included 240 adult respondents from the general population of Japan in total (female 50%; mean age, 44.5 years; and mean BMI, 22.4 kg/m2). The mean (95% confidence interval) health state utility tended to decrease as BMI category increased, as follows: 0.827 (0.804-0.849) for ≥25 to <30 kg/m2, 0.604 (0.563-0.645) for ≥30 to <35 kg/m2, 0.771 (0.741-0.800) for ≥25 to <35 kg/m2, and 0.317 (0.255-0.380) for ≥ 35 kg/m2.

CONCLUSIONS

The results of this TTO study in the general population of Japan demonstrate that an increase in BMI from 25 kg/m2 upward is associated with a decrease of health state utilities. These findings can be utilized to perform cost-effectiveness analyses of anti-obesity medications in Japan.