Original Contribution Trajectories of Body Mass Index and Their Associations With Mortality Among Older Japanese: Do They Differ From Those of Western Populations?

Few studies have focused on the relationship between the trajectories of long-term changes in body mass index (BMI; weight (kg)/height (m)2) and all-cause mortality in old age, particularly in non-Western populations. We eval-uated this association by applying group-basedmixture models to data derived from the National Survey of the Jap-anese Elderly, which included 4,869 adults aged 60 or more years, with up to 7 repeated observations between 1987 and 2006. Four distinct BMI trajectories were identified: “low-normal weight, decreasing ” (baseline BMI = 18.7; 23.8 % of sample); “mid-normal weight, decreasing ” (baseline BMI = 21.9; 44.6 % of sample); “high-normal weight, decreasing ” (baseline BMI = 24.8; 26.5 % of sample); and “overweight, stable ” (baseline BMI = 28.7; 5.2 % of sam-ple). Survival analysis with an average follow-up of 13.8 years showed that trajectories of higher BMI were associ-ated with lower mortality. In particular, relative to those with a mid-normal weight, decreasing BMI trajectory, those with an overweight, stable BMI trajectory had the lowest mortality, and those with a low-normal, decreasing BMI trajectory had the highest mortality. In sharp contrast with prior observations from Western populations, BMI changes lie primarily within the normal-weight range, and virtually no older Japanese are obese. The association between BMI trajectories and mortality varies according to the distribution of BMI within the population. body mass index; Japan; mortality; older adults; trajectories Abbreviations: ADL, activity of daily living; BMI, body mass index; CI, confidence interval