title: Proportion of dementia in Australia explained by common modifiable risk factors.
abstract: BACKGROUND
  At present, dementia has no known cure. Interventions to delay onset and reduce prevalence of the disease are therefore focused on risk factor reduction. Previous population attributable risk estimates for western countries may have been underestimated as a result of the relatively low rates of midlife obesity and the lower weighting given to that variable in statistical models.
  
  
  METHODS
  Levin's Attributable Risk which assumes independence of risk factors was used to calculate the proportion of dementia attributable to seven modifiable risk factors (midlife obesity, physical inactivity, smoking, low educational attainment, diabetes mellitus, midlife hypertension and depression) in Australia. Using a recently published modified formula and survey data from the Australia Diabetes, Obesity and Lifestyle Study, a more realistic population attributable risk estimate which accounts for non-independence of risk factors was calculated. Finally, the effect of a 5-20% reduction in each risk factor per decade on future dementia prevalence was computed.
  
  
  RESULTS
  Taking into consideration that risk factors do not operate independently, a more conservative estimate of 48.4% of dementia cases (117,294 of 242,500 cases) was found to be attributable to the seven modifiable lifestyle factors under study. We calculated that if each risk factor was to be reduced by 5%, 10%, 15% and 20% per decade, dementia prevalence would be reduced by between 1.6 and 7.2% in 2020, 3.3-14.9% in 2030, 4.9-22.8% in 2040 and 6.6-30.7% in 2050.
  
  
  CONCLUSIONS
  Our largely theory-based findings suggest a strong case for greater investment in risk factor reduction programmes that target modifiable lifestyle factors, particularly increased engagement in physical activity. However, further data on risk factor treatment and dementia risk reduction from population-based studies are needed to investigate whether our estimates of potential dementia prevention are indeed realistic.
authors.affiliation: Centre for Research on Ageing, Health and Wellbeing, The Australian National University, Florey, Building 54, Mills Road, Acton, ACT 2601, Australia. kimberlyashbymitchell@gmail.com.
authors.forename: Kimberly
authors.identifier: http://orcid.org/0000-0002-4709-2737
authors.initials: K
authors.lastname: Ashby-Mitchell
authors.affiliation: Centre for Research on Ageing, Health and Wellbeing, The Australian National University, Florey, Building 54, Mills Road, Acton, ACT 2601, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Burns
authors.affiliation: Baker IDI Heart and Diabetes Institute, 75 Commercial Road, Melbourne, VIC, 3004, Australia.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Shaw
authors.affiliation: Centre for Research on Ageing, Health and Wellbeing, The Australian National University, Florey, Building 54, Mills Road, Acton, ACT 2601, Australia.
authors.forename: Kaarin J
authors.initials: KJ
authors.lastname: Anstey
mesh_terms: D001315:Australia / Q000453:epidemiology; D003704:Dementia / Q000453:epidemiology* / Q000517:prevention & control; D003920:Diabetes Mellitus / Q000453:epidemiology; D004522:Educational Status; D006801:Humans; D006973:Hypertension / Q000453:epidemiology; D009765:Obesity / Q000453:epidemiology; D015995:Prevalence; D012307:Risk Factors; D040242:Risk Reduction Behavior; D057185:Sedentary Behavior; D012907:Smoking / Q000453:epidemiology
keywords: Australia; Dementia; Population attributable risk