Summary
As New Zealand’s population ages, dementia rates are projected to double by 2050. New research is providing stronger evidence that mental health disorders, particularly depression, anxiety, and bipolar disorder, significantly increase dementia risk, especially when severe. Psychological distress more than doubles dementia risk, and people with poorer self-rated health are also at higher risk.
Mental health challenges are rising in Aotearoa New Zealand (NZ), yet unmet need for services has also grown, highlighting a care gap. The evidence underscores the need for early, sustained investment in mental health. This means a life course approach and whole-of-government action to reduce social and economic disadvantage, promote wellbeing, and lower population-level dementia risk.
The risk of dementia increases steeply with age. As the Aotearoa New Zealand (NZ) population ages, the number of people with dementia is projected to double from 83,000 in 2025 to 167,000 by the year 2050.1
In the absence of a cure, there is a need to focus on reducing dementia risk and it is estimated that almost half of dementias worldwide are preventable if 14 potentially modifiable “risk factors” for dementia were completely eliminated.2 These risk factors broadly fall into two groups. Firstly, factors that result in damage to the brain: diabetes, high cholesterol, hypertension, smoking, obesity, air pollution, head injury, physical inactivity, high alcohol use, and untreated depression. Secondly, factors that reduce cognitive reserve, the brain’s ability to tolerate damage: low education, uncorrected hearing or vision loss, and social isolation. While depression is the only mental health disorder currently included as a risk factor, other mental health disorders including anxiety, bipolar disorder, and psychotic disorders likely increase dementia risk.2
Indeed, our new research, published in International Psychogeriatrics, finds that adults in NZ who have ever been diagnosed with a mental health disorder face increased risk of developing dementia later in life. 3 Using data from the NZ Health Survey, we followed up adults who had reported being diagnosed by a doctor with depression, anxiety, or bipolar disorder to identify how many were subsequently diagnosed with dementia.
We found that anxiety was associated with a 30% higher risk of dementia, depression with a 40% higher risk, and bipolar disorder with almost a threefold increase. Our study aimed to quantify dementia risk associated with mental health disorders in the general population, most of whom are managed in the community or primary care rather than hospital settings.
Rates of mental health disorders and psychological distress in NZ are increasing but so is unmet need
These findings add to a growing body of evidence linking mental health conditions with later-life dementia risk. A 2022 NZ study reported that the risk of dementia tripled in people hospitalised for anxiety disorders, quadrupled for mood disorders (depression or bipolar disorder), and was over six times higher for those with psychotic disorders. However, hospitalisation reflects more severe illness, and many people with mental health disorders are treated in the community. Our findings confirm that increased dementia risk is also present at a population level.
There is growing evidence that the prevalence of mental health distress and disorders in NZ has increased over the last decade. Between 2016 and 2023 rates of people reporting moderate to severe anxiety or depression symptoms increased by more than 50%.4 A similar trend is seen in psychological distress, with over 50% more people reporting high or very high levels of distress. 5 It is concerning that reported unmet need for mental health and addiction services also rose by 50% over this period, suggesting that growing demand is not being met.4
Mental health disorders in Aotearoa are associated with increased dementia risk
Mental health disorders can increase the risk of dementia through both biological and psychosocial avenues. Chronic stress can lead to changes in the brain while some psychiatric medications, such as antipsychotics, have also been linked to an increased dementia risk. Mental health disorders are also associated with health behaviours that result in poorer physical and mental wellbeing such as higher rates of smoking and alcohol use and lower rates of physical activity and social interaction. 3
Psychological distress and self-perception of overall health are associated with increased dementia risk
There is growing evidence of an association between a person’s own assessment of their physical or psychological health and dementia risk.6 7 Our research demonstrates that the risk of dementia is doubled in people reporting psychological distress and tripled in those who experience more severe distress. We also have preliminary evidence that those who rate their overall health less favourably are at an increased risk of dementia. New Zealanders who rated their health as poor had triple the risk of dementia compared to those rating their health as excellent, even after accounting for existing physical or mental health disorders, or psychological distress. (Kimpton, unpublished research)
A life course approach to mental health and wellbeing is needed
While dementia is seen as a disease of older people, it is the end result of incremental and cumulative damage to the brain over decades. Mental health and wellbeing are shaped by the complex interplay of social and environmental factors across the life course. Early life experiences play a critical role in shaping long-term mental health outcomes. Chronic stressors associated with deprivation include economic instability, food insecurity, and environmental factors such as air quality, noise and access to green spaces.8
As with other risk factors for dementia, change on an individual level is unlikely without broader population-level approaches that address the environment within which people live, work, and play. Effective policies and interventions will require a whole-of-government approach to address the health inequities associated with poverty and social disadvantage.
What this Briefing adds
- Rates of people reporting anxiety and depression symptoms in Aotearoa are increasing but so too are the rates of unmet need
- Mental health disorders are associated with an increased risk of dementia and more severe illness is associated with higher risk
- Psychological distress doubles the risk of dementia and almost triples the risk in those with more severe distress
- Perceptions of poor overall health are associated with an increased risk of dementia, with those who rate their health as poor having twice the risk of dementia
Implications for policy
- Urgent action is needed on mental health in the face of rising rates of mental health disorders and increasing levels of unmet need. Timely and appropriate treatment of mental health disorders will reduce dementia risk
- The association between dementia risk and psychological distress more generally emphasises the need for broader initiatives to promote resilience and mental wellbeing in our communities
- Mental health and wellbeing are shaped by childhood experiences, and life stressors are amplified by poverty and social disadvantage. A life course approach is needed to promote mental health and wellbeing from early life.
- Effective policies and interventions will require a whole-of-government approach to address the health inequities associated with poverty and social disadvantage.
Authors details
Dr ‘Etuini Ma’u, Department of Psychological Medicine, University of Auckland | Waipapa Taumata Rau
Associate Professor Sarah Cullum, Department of Psychological Medicine, University of Auckland | Waipapa Taumata Rau
Associate Professor Gary Cheung, Department of Psychological Medicine, University of Auckland | Waipapa Taumata Rau
