Incidence of dementia

Understanding the number of new dementia cases in a given period, also known as the incidence of dementia, is important for responding to the changing and growing challenges that dementia poses. The issues and gaps discussed in the Prevalence of dementia page are also applicable to dementia incidence data. Estimating dementia incidence requires even more information, such as date of diagnosis and whether a diagnosis was made close to symptom onset.

Emerging evidence suggests the incidence rate of dementia is declining in several high-income countries due to improvements in the prevention and management of vascular risk factors for dementia (i.e. high blood pressure and cardiovascular disease) (Roehr et al. 2018). This decline has been seen despite rising cases globally of other risk factors for dementia, such as diabetes and obesity. It isn’t clear whether a declining incidence applies to Australia as we do not know the net effects of changing dementia risk factors coupled with an ageing population. For example, Australia’s obesity rates are among the highest of OECD nations but its mortality rate due to coronary heart disease lies just below the OECD average (AIHW 2020).

Given the unique and changing profile of Australia’s population and the lack of Australian-specific studies on dementia incidence, we have chosen not to present national dementia incidence estimates. Recent and emerging work to improve dementia prevalence and incidence estimates provide a good prospect for the availability of these statistics in coming years.

Emerging Australian work to better understand dementia incidence

The following 3 examples illustrate the important knowledge that can be gained from population-wide, high-quality data on dementia incidence.

The Sydney Memory and Ageing Study

This ongoing population-based longitudinal study has provided important information about dementia incidence among older community-dwelling adults (aged 70–90) since 2005. The study provides high-quality information by using reliable, standardised assessments of mild cognitive impairment and dementia among older Australians. Of those adults in the study with no cognitive impairment, 9.5% developed dementia over 6 years. Of participants with mild cognitive impairment, 4.7% developed dementia 2 years later (Lipnicki et al. 2017).

45 and Up Study

The 45 and Up Study is the largest ongoing study of healthy ageing in the southern hemisphere. A cohort of about a quarter of a million participants from the 45 and Up Study has been linked to health administrative data such as hospitals and prescription data, to ascertain dementia incidence rates. Recent estimates place the age-adjusted incidence rate of dementia at 16.8 cases per 1,000 person years for people aged 65 and over (Welberry et al. 2020).

NHMRC-funded dementia research grants

The National Health and Medical Research Council (NHMRC) through the then National Institute for Dementia Research has funded research grants exploring the utility of linked health administrative data (such as hospitals and deaths data) and electronic health records, to better identify dementia and develop new methodological approaches to estimate dementia prevalence and incidence (NHMRC 2019).

The NHMRC has also funded the development of a dementia clinical quality registry to directly collect data for the diagnosis and management of dementia by the Australia Dementia Network, which could be used in the future to estimate dementia incidence using high-quality clinical data (NHMRC 2019).