Birth cohort differences in multimorbidity over time among Chinese oldest-old adults

Multimorbidity imposes a significant burden on healthcare systems worldwide. Understanding longitudinal changes multimorbidity among the oldest-old (i.e., those aged 80 or more) is essential yet remains limited. This study investigated birth cohort differences in multimorbidity over time among Chinese oldest-old adults using two longitudinal surveys in different decades.

Data were drawn from the Chinese Longitudinal Healthy Longevity and Happy Family Study. 2703 and 2533 participants aged 80 or more were included in the 1998 and 2008 surveys, both with a one-decade follow-up, respectively. The multimorbidity count was assessed as the number of conditions an individual had from a list of 12 common chronic conditions. Generalized linear mixed models were employed to assess birth cohort differences, adjusting for demographic, lifestyle, and socioeconomic factors. Inverse probability weighting was applied to mitigate attrition bias.

The 1998 survey (mean age: 89.32 ± 6.87 years, 51.17 % female) revealed no significant birth cohort differences in multimorbidity (P > 0.05). In contrast, the 2008 survey (mean age: 91.12 ± 7.13 years, 59.97 % female) demonstrated that each successive birth cohort experienced a higher multimorbidity count than its predecessors (P < 0.05). Compared to the cohort born in 1924-1928, participants from the cohort born in 1909-1913 had an estimated 0.217 fewer multimorbidity count (95 % CI: -0.397, -0.037), whereas those from the cohort born in 1919-1923 exhibited a reduction of 0.094 (95 % CI: -0.185, -0.002). Additionally, the multimorbidity count was significantly higher among smokers, alcohol consumers, and those with a lower intake of fresh fruit.

Multimorbidity is progressively increasing among recent birth cohorts among Chinese oldest-old adults. These findings highlight the urgent need for comprehensive policies and early interventions to promote healthy ageing.