Author(s): Riccardo E. Marioni 1 , * , Michael J. Valenzuela 2 , Ardo van den Hout 3 , Carol Brayne 1 , Fiona E. Matthews 4 , MRC Cognitive Function and Ageing Study 1
The ageing of modern nations is set to radically alter the nature of society, arguably with no greater impact than on the prevalence and cost implications of dementia. Currently, 800,000-900,000 persons suffer from dementia in the UK, with an annual estimated cost to the economy of Â£22-23 billion . Whilst mortality rates for stroke, heart disease and other common causes of death declined between 2000 and 2008, the equivalent figure for Alzheimer's dementia rose by 66% . By 2050, dementia prevalence is expected to nearly quadruple to over 115 million worldwide  and at the same time the proportion of tax-paying workers to retirees will fall by 40% . Projections in Australia suggest that assuming the status quo , dementia-related care in 2060 would consume the entire current health budget , clearly an unsustainable scenario that will force unenviable health decisions by policy makers.
Given these forecasts, identification of modifiable factors that reduce the risk of developing severe cognitive impairment or encourage cognitive recovery from mild cognitive impairment (MCI) to a non-cognitively impaired state are highly sought after. MCI describes a stage of intermediate cognitive dysfunction where the risk of 'conversion' to dementia is increased but is by no means guaranteed . Indeed, it is possible for individuals to revert from a diagnosed MCI state back to a normal, non-impaired cognitive state over time .
There is considerable evidence to support a link between an active cognitive lifestyle and a decreased risk of cognitive decline and dementia , . Previously, we have found that greater cognitive lifestyle, denoted by education, occupational complexity and late-life social engagement, was predictive of decreased dementia incidence over and above other known risk factors . However, this paper did not explore the link between cognitive lifestyle and cognitive decline. Furthermore, whilst each individual factor was itself not independently predictive of lower risk, the combination of a higher level of education plus either a more complex occupation or late life social engagement decreased prospective dementia risk by 40%. This may explain why reviews of these components in isolation have been mixed -. Active participation in any single cognitive lifestyle factor appears not to be sufficiently powerful to modify dementia risk, but ongoing engagement throughout the lifespan may accumulate and provide additive or synergistic value.
Whether the same is true in models of cognitive decline is not clear. Recently, we showed that an active cognitive lifestyle was associated with a decreased risk of cognitive decline, an increased chance of cognitive recovery, but an increased mortality risk from the most severely impaired cognitive state . However, this paper did not break down cognitive lifestyle into its individual components but instead used an overall summary score, measured as a weighted linear combination of education, occupation and social engagement.
We now extend this work by...