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The less healthy your lifestyle, the more you are at risk of developing dementia in later life, a new systematic review has shown. Researchers analysed the results of 18 studies with over 44,000 participants.
Having two or more ‘modifiable risk factors’, including smoking, high blood pressure, poor diet, inactivity, obesity and excessive alcohol consumption, puts adults at greater risk of developing dementia.
The included studies followed up people without signs of cognitive decline to see who developed dementia of any cause.
A third of the studies could be combined in a meta-analysis and these showed a 20% increase in the risk of dementia for one risk factor, which rose to 65% for two risk factors. The presence of three risk factors doubled the risk of dementia. Other individual studies were compatible with this pooled estimate.
These results are consistent with our growing knowledge of the links between unhealthy lifestyles and dementia.
Why was this study needed?
Dementia affects around 850,000 people in the UK. With an ageing population, the Government has estimated that this figure will rise to two million by 2050. The cost to society is around £26 billion per year.
We know that the modifiable risk factors for cognitive decline and dementia include smoking, lack of physical exercise, poor diet, more than minimal alcohol intake, mid-life obesity, high blood pressure, high cholesterol and diabetes. This study looked at the cumulative impact of several of these risk factors on the risk of future cognitive decline and dementia.
What did this study do?
This systematic review included 18 prospective studies with over 40,000 participants. Eight studies were from the US, three from Sweden, two from the Netherlands, and one each from the UK, Finland, Germany, France, Australia and South Korea. The duration of follow-up ranged from 22 months to over 20 years.
The studies varied in which and how many risk factors they looked at. Five studies looked at the inverse of risk factors and reported on protective healthy behaviours.
The majority of the studies had a low or medium risk of bias. There was limited opportunity to combine results from the studies (only six of the 18 studies) due to differences in how they reported results. However, the research methods were appropriate, and the results appear reliable.
What did it find?
- Across the included studies, there was a consistent increased risk of dementia associated with greater numbers of risk factors or unhealthy behaviours, and the opposite for healthy or protective behaviours.
- The pooled increased risk of any type of dementia with one risk factor was 1.20 (95% confidence interval [CI] 1.04 to 1.39); with two risk factors it was 1.65 (95% CI 1.4 to 1.94); and with three risk factors it was 2.21 (95% CI 1.78 to 2.73).
- No clear differences in the results were observed by baseline age group – for instance by age at the beginning of the study or for length of follow-up.
What does current guidance say on this issue?
NICE recommends in its 2015 guideline that adults in mid-life are encouraged to adopt healthy behaviours that can reduce their risk of dementia, and be made aware of the links between lifestyle and later-life dementia.
NICE advises that public health bodies should commission initiatives and campaigns aimed at helping people to stop smoking, be more active, reduce their alcohol consumption, improve their diet and achieve and maintain a healthy weight.
NICE states that commissioners should include dementia risk reduction when developing strategies to address other chronic health conditions such as cardiovascular disease and diabetes.
What are the implications?
The consistent relationship demonstrated between lifestyle risk factors and dementia provides further evidence for public health organisations in terms of raising awareness. The overlap with risk factors for cardiovascular disease and cancer is likely to mean that lifestyle public health interventions could benefit all of them.
This meta-analysis is a useful attempt to quantify the effect of risk factor accrual for dementia. It looked only at widely known and accepted ‘modifiable risk factors’. So, for example, risk factors such as air pollution weren’t included. Further research will be needed to effectively target the most at-risk groups of people.
Citation and Funding
Peters R, Booth A, Rockwood K et al. Combining modifiable risk factors and risk of dementia: a systematic review and meta-analysis. BMJ Open. 2019;9:e022846.
No specific funding was received for this study. Individual authors are funded by a range of institutions including the Australian Dementia Collaborative Research Centre; the University of Sheffield; the Dalhousie Medical Research Foundation; the Canadian Institutes of Health Research, the Canadian Frailty Network and the Fountain Family Research Fund of the Queen Elizabeth II Health Sciences Centre.
Bibliography
Frankish H and Horton R. Prevention and management of dementia: a priority for public health. The Lancet. 2017;390:2614-5.
NHS website. Alcohol support. Alcohol Units. London: Department of Health and Social Care; updated 2018.
NICE. Dementia, disability and frailty in later life – mid-life approaches to delay or prevent onset. NG16. London: National Institute for Health and Care Excellence; 2015.
Public Health England. Dementia: applying All Our Health. London: Department of Health and Social Care; 2018.
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