Does Early or Timely Diagnosis Benefit People with Dementia and Their Carers? A Systematic Review

Background: Global dementia policies advocate for early or timely diagnosis, yet evidence on benefits or harms remains limited. This systematic review evaluates quantitative evidence comparing outcomes of early versus late and timely versus untimely dementia diagnoses. Methods: Following PRISMA guidelines, the protocol was registered on PROSPERO. Comprehensive searches of PsycINFO, Medline, Embase, SCOPUS, and CINAHL were conducted without date restrictions. Eligible studies defined diagnostic timing and examined associations with outcomes for people with dementia and/or carers. Quality was appraised using the QuADS tool, and data were narratively synthesised. Results: Four studies (2018–2021) met inclusion criteria, encompassing 37,341 individuals with dementia and 1409 carers across Europe and the United States. Three studies investigated early versus late diagnosis; one assessed perceived timeliness. Definitions varied. Evidence of benefit was limited: one study reported a 9–23% reduction in mortality risk for early diagnosis. Another found that carers perceiving the diagnosis as untimely experienced greater and more persistent emotional distress. No significant associations were observed for cognitive or functional decline, hospitalisation, or emergency department attendance. Conclusions: Despite strong policy endorsement, empirical evidence on benefits of early or timely dementia diagnosis remains scarce, geographically narrow, and methodologically constrained. Future longitudinal studies explicitly defining diagnostic timing and incorporating psychosocial and contextual factors are needed to clarify potential benefits or harms for people with dementia and their carers.