Mild cognitive impairment (MCI) in the population : new criteria and cohort effects

Abstract

Much work on identifying individuals at high risk of dementia has focused on the clinical concept of MCI, which is considered to be an intermediate state between normal cognitive ageing and dementia. Many definitions for this state exist, including for example amnestic-MCI and Other Cognitive Impairment no Dementia (OCIND). This study utilises the Cognitive Function and Ageing Studies (CFAS) I & II, to explore the concept of MCI in the UK population. The first study focused on updating the definition of MCI and established a cognitive spectrum to capture participants of CFAS with no cognitive impairment through to dementia. The definitions were then used to estimate the UK population prevalence of MCI. A natural progression was to use the follow-up (wave II) of CFAS II to determine the incidence and progression of MCI and OCIND. The final study focused on risk factors associated with prevalent MCI, OCIND and dementia, as well as incident cognitive impairment. The link between cognitive function and both socio demographic factors (i.e. education, deprivation and loneliness) and medical co morbidities (i.e. Parkinson’s disease, heart attack and diabetes) were investigated. Mild dementia has, along with CFAS defined dementia, declined, (5.7%, 95% CI: 3.8, 8·1) in 1991 to 315,142 (3.0%, 95% CI: 2.4, 3.8) in 2011. There is a clear increase in the prevalence of OCIND with MCI remaining stable. In CFAS II the overall incidence rate for RMCI, is 138.5 per 1000-person years (95% CI: 131.5, 145.5) and 233.5 per 1000-person years (95% CI: 228.4, 238.6) for OCIND. Key risk factors for incident MCI and transition to dementia were smoking status, loneliness and poor self reported health. The analysis highlights the need to move beyond the current narrow dementia criteria which exclude large proportions of older people with cognitive impairment. Findings suggest that the increase in OCIND and stability of MCI could reflect “normal cognitive ageing” among a population which is substantially older. Evidence suggests it is through healthy lifestyle behaviours, better educational attainment, minimizing risks from comorbidities in the wider population which should be further encouraged to reduce risk of cognitive impairment.