The Role of Underweight in Active Life Expectancy Among Older Adults in Japan

It is underweight, rather than overweight or obesity, that has been a pressing public health concern in Japan. This study examines the impact of being underweight on the health of older Japanese men and women, measured by active life expectancy at age 65. Following the Japanese government's guideline, underweight in this study is defined using the body mass index (BMI) value of 20.

Data came from five waves (1999-2009) of the Nihon University Japanese Longitudinal Study of Aging (NUJLSOA). We used the Interpolation of Markov Chain approach to estimate the number of years underweight (BMI < 20), normal weight (20 < BMI < 25), and overweight (25 < BMI) individuals were expected to live without difficulty in activities of daily living (ADLs) or instrumental ADLs.

We found differences in life and health expectancies across the three weight categories. Underweight people were expected to live the shortest lives and spend the fewest years in an active state compared with normal and overweight individuals. Results remained unchanged even when accounting for educational attainment, smoking history, and a count of existing chronic conditions.

Being underweight is associated with poor quality of life lived among Japanese older adults. This finding suggests the importance of maintaining proper weight and avoids nutritional risks at advanced ages.