Distribution characteristics of body mass index in Chinese older adults of advanced ages under the new standard: based on data from the China Nutrition and Health Surveillance (2015–2017)

Objective To investigate body mass index (BMI) level of older adults aged 80 years and above in China under the new BMI recommendation standard and analyze the distribution characteristics of people with different BMI levels.

Methods A total of 3 262 older adults of advanced ages from the China Nutrition and Health Surveillance (2015– 2017) were included. The appropriate BMI level of them was determined by the latest The Appropriate Range of Body Mass Index and Body Weight Management Standards for the Oldest Old published in 2025. The results were weighted and adjusted by the sixth census data of the National Bureau of Statistics. The Rao-Scott chi-square test based on complex sampling design correction was performed to analyze the distribution characteristics of BMI among the older adults of advanced ages.

Results The weighted mean BMI of the older adults aged 80 years and above in China was (23.5±0.2) kg/m² in urban areas and (22.4±0.2) kg/m² in rural areas in 2015–2017. The overall distribution trends of BMI among the older adults of advanced ages were similar in urban and rural areas in China, while the BMI level in rural areas was slightly lower than that in urban areas (F = 20.94, P < 0.01). Under the new standard, 44.6% of the older adults of advanced ages had a BMI in the appropriate range, and 43.0% had a BMI below the appropriate range. The proportions of the older adults of advanced ages living in rural areas (65.3%) or in the central and western China (34.4% and 25.0%), with primary school education or below (89.8%), and with lower per capita annual dietary expenditure (23.0%) who had BMI below the appropriate range were higher (P < 0.01).

Conclusions Under the new appropriate BMI range standard, the BMI of older adults aged 80 or above in China is at a medium to low level, suggesting that the current nutritional problems of this population in China are still dominated by undernutrition. Understanding the BMI level and distribution characteristics of this population under the new standard can provide new data support for the health management of key populations.