[Distribution characteristics of body mass index among Chinese oldest-old aged 80 years and above].

Objective: To investigate body mass index (BMI) level, identify the main type of nutritional problem, and describe the population distribution characteristics of BMI among Chinese people aged 80 years or above. Methods: The data of 9 481 oldest-old individuals were obtained from the 2017-2018 Chinese Longitudinal Healthy Longevity Survey. The Lambda-Mu-Sigma method, weighted estimates of BMI, and comparisons by BMI quintiles were used to describe the BMI level and distribution characteristics among the oldest-old. Results: The average age of the participants was (91.9±7.7) years, with P50 of the weighted BMI at 21.9 (95%CI: 21.8-22.0) kg/m2. The result of BMI level showed a decreasing trend with age, with a rapid decline before age 100, and then the trend became slower. There are about 30% of the oldest-old classified as undernutrition, but the prevalence of overnutrition is only about 10%. The population distribution characteristics by BMI quintiles showed the oldest-old with lower BMI levels were likely to have the following characteristics: sociodemographically, to be older, female, ethnic minority, unmarried/divorced/widowed, rural residents, illiterate, with inadequate living expenses, located in Central, South, or Southwest China; regarding lifestyles, lower BMI levels were observed for participants who were smoking, not exercising, lack of leisure activities, or with poor dietary diversity; considering functional status, participants with lower BMI levels were those who have poor chewing ability, disability in activities of daily living, cognitive impairment, hearing loss, visual impairment, or poor self-rated health status. The oldest-old with higher BMI levels were likely to have heart disease, hypertension, cerebrovascular disease, and diabetes. Conclusions: The overall BMI level was low among the Chinese oldest-old and it showed a downward trend with age. Currently, the main nutritional problem among the Chinese oldest-old was undernutrition rather than overweight or obesity. Management of healthy lifestyles, functional status, and diseases would be helpful to reduce the risk of undernutrition among the oldest-old.目的： 研究中国≥80岁高龄老年人体质指数（BMI）水平，确定高龄老年人主要营养不良问题类型及不同BMI水平人群分布特征。 方法： 共纳入中国老年健康影响因素跟踪调查2017-2018年横断面研究9 481名高龄老年人数据，通过偏度-中位数-变异系数法、加权均值计算和五分位数分组分析等描述高龄老年人BMI水平及其分布特征。 结果： 研究对象年龄为（91.9±7.7）岁，加权BMI水平的P50为21.9（95%CI：21.8~22.0）kg/m2。BMI水平随年龄增长总体呈下降趋势，100岁前下降较快，之后趋势变得平缓。约30%的高龄老年人存在营养不足问题，而营养过剩的比例仅约10%。BMI五分位数人群分布特征表明，BMI水平较低的高龄老年人具有的特征：人口社会经济学上，年龄较大、女性、少数民族、未婚/离异/丧偶、在农村居住、未接受过教育、生活费水平不足、位于华中、华南和西南地区；生活方式上，吸烟、不锻炼、休闲活动缺乏、膳食多样性差；功能状态上，咀嚼能力差、日常生活自理能力损伤、认知功能损伤、听力损伤、视力损伤、自评健康状况差；患心脏病、高血压、脑血管疾病和糖尿病的高龄老年人BMI水平较高。 结论： 中国高龄老年人BMI总体水平较低，且随年龄增加呈下降趋势。目前中国高龄老年人的主要营养问题类型为营养不足而非营养过剩，进行健康生活方式、功能状态和疾病管理有利于降低高龄老年人营养不足风险。.