The oldest-old population, those aged ≥ 80 years, is the fastest-growing group in the United States (US), grappling with an increasingly heavy burden of dementia. We aimed to dissect the trends in dementia prevalence, mortality, and risk factors, and predict future levels among this demographic. Leveraging data from the Global Burden of Disease Study 2019, we examined the trends in dementia prevalence, mortality, and risk factors (with a particular focus on body mass index, BMI) for US oldest-old adults. Through decomposition analysis, we identified key population-level contributors to these trends. Predictive modeling was employed to estimate future prevalence and mortality levels over the next decade. Between 1990 and 2019, the number of dementia cases and deaths among the oldest-old in the US increased by approximately 1.37 million and 60,000 respectively. The population growth and aging were highlighted as the primary drivers of this increase. High BMI emerged as a growing risk factor. Females showed a disproportionately higher dementia burden, characterized by a unique risk factor profile, including BMI. Predictions for 2030 anticipate nearly 4 million dementia cases and 160,000 related deaths, with a marked increase in prevalence and mortality anticipated among those aged 80–89. The past 30 years have witnessed a notable rise in both the prevalence and mortality of dementia among the oldest-old in the US, accompanied by a significant shift in risk factors, with obesity taking a forefront position. Targeted age and sex-specific public health strategies that address obesity control are needed to mitigate the dementia burden effectively.

美国最年长的老年人口（≥ 80 岁）是增长最快的群体，正在应对日益沉重的痴呆症负担。我们的目的是剖析痴呆症患病率、死亡率和风险因素的趋势，并预测该人群的未来水平。利用 2019 年全球疾病负担研究的数据，我们研究了美国最年长老年人痴呆症患病率、死亡率和风险因素（特别关注体重指数，BMI）的趋势。通过分解分析，我们确定了这些趋势的关键人口层面贡献因素。采用预测模型来估计未来十年的患病率和死亡率水平。 1990年至2019年间，美国高龄老人的痴呆症病例和死亡人数分别增加了约137万和6万人。人口增长和老龄化被认为是这一增长的主要驱动力。高体重指数已成为一个日益严重的风险因素。女性表现出不成比例的较高痴呆症负担，其特点是独特的危险因素，包括体重指数。预计到 2030 年，将有近 400 万痴呆病例和 16 万相关死亡病例，其中 80-89 岁人群的患病率和死亡率将显着增加。过去 30 年，美国老年人中痴呆症的患病率和死亡率显着上升，同时危险因素也发生了显着变化，其中肥胖占据首位。需要针对肥胖控制的有针对性的年龄和性别公共卫生策略，以有效减轻痴呆症负担。