Population decline, particularly through aging, is reshaping demographic structures and placing increasing pressure on health and care systems. However, the mechanisms linking these changes to late-life health outcomes and the functioning of medical systems remain insufficiently understood. Here, we examine the dynamic interrelationships among population change, Alzheimer’s mortality as a representative late-life outcome, and treatment- and caregiving-oriented medical infrastructure. We show that increases in population are followed by sustained declines in Alzheimer’s mortality over the medium to long term, whereas depopulating regions exhibit persistently rising mortality despite expansions in long-term care facilities. In contrast, treatment-oriented medical infrastructure is consistently associated with lower mortality. These findings reveal an imbalance in which caregiving capacity expands where treatment capacity contracts. Policies prioritizing treatment-oriented systems, particularly early diagnosis and intervention, are critical for mitigating late-life mortality risks under sustained population decline.