Abstract
This study examined the association between the trajectories of body mass index (BMI) and all-cause mortality in old age. Data came from the National Survey of the Japanese Elderly, which included 4,869 adults aged 60 and over, with up to seven 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 sample). Survival analysis showed that, relative to those with mid-normal decreasing BMI, those with stable overweight trajectory had the lowest mortality, whereas those with low-normal, decreasing BMI had the highest mortality. In a sharp contrast with prior observations from Western populations, BMI changes primarily lie within the normal-weight range and virtually none are obese among older Japanese. The association between BMI trajectories and mortality varies according to the distribution of BMI within the population.