Habitual fasting duration and accelerated multimorbidity in older adults

BACKGROUND: Prolonged fasting has been linked to metabolic benefits in younger adults, but its effects on chronic diseases in older populations remain unclear. OBJECTIVE: To examine the association between habitual fasting duration and 15-year chronic disease accumulation in older adults, overall, within organ systems, and between age groups. METHODS: Data were drawn from the Swedish National study on Aging and Care in Kungsholmen, a longitudinal population-based cohort of 2981 predominantly community-dwelling adults aged ≥60 years. Habitual fasting duration was the longest interval between two typical eating occasions within a 24-h window. Multimorbidity was the total number of chronic diseases (out of 60) at each visit, analyzed overall and within cardiovascular, neuropsychiatric, and musculoskeletal organ systems. Multivariate linear mixed models estimated the association between habitual fasting duration and the annual rate of multimorbidity accumulation, overall and stratified by age (<78 vs. ≥78 years). RESULTS: Compared with the lowest habitual fasting quartile (6-11.5 h), participants in the highest quartile (14-24 h) experienced steeper annual accumulation of total chronic diseases (β = 0.119; 95% confidence interval: 0.070, 0.167), cardiovascular diseases (0.022 [0.006, 0.038]), and neuropsychiatric diseases (0.019 [0.005, 0.033]), but not musculoskeletal diseases. The association with total chronic disease accumulation was apparent in adults aged ≥78 years (β = 0.099 [0.031, 0.168]) but absent in those <78 years (-0.009 [-0.078, 0.061]). Findings remained consistent across sensitivity analyses addressing reverse causation, measurement bias, and residual confounding. CONCLUSION: In older adults, particularly the older old, longer habitual fasting duration was associated with faster chronic disease accumulation, suggesting it may be detrimental in advanced age.