Potential for primary prevention of Alzheimer's disease: an analysis of population-based data
Norton S, Matthews FE, Barnes DE, Yaffe K, Brayne C (2014) The Lancet - Neurology 13 788 - 794
Web URL: Read more on the Lancet website
Abstract:
Background
Recent estimates suggesting that over half of Alzheimer's disease burden worldwide might be attributed to potentially modifiable risk factors do not take into account risk-factor non-independence. We aimed to provide specific estimates of preventive potential by accounting for the association between risk factors.
Methods
Using relative risks from existing meta-analyses, we estimated the population-attributable risk (PAR) of Alzheimer's disease worldwide and in the USA, Europe, and the UK for seven potentially modifiable risk factors that have consistent evidence of an association with the disease (diabetes, midlife hypertension, midlife obesity, physical inactivity, depression, smoking, and low educational attainment).
The combined PAR associated with the risk factors was calculated using data from the Health Survey for England 2006 to estimate and adjust for the association between risk factors. The potential of risk factor reduction was assessed by examining the combined effect of relative reductions of 10% and 20% per decade for each of the seven risk factors on projections for Alzheimer's disease cases to 2050.
The combined PAR associated with the risk factors was calculated using data from the Health Survey for England 2006 to estimate and adjust for the association between risk factors. The potential of risk factor reduction was assessed by examining the combined effect of relative reductions of 10% and 20% per decade for each of the seven risk factors on projections for Alzheimer's disease cases to 2050.
Findings
Worldwide, the highest estimated PAR was for low educational attainment (19·1%, 95% CI 12·3—25·6). The highest estimated PAR was for physical inactivity in the USA (21·0%, 95% CI 5·8—36·6), Europe (20·3%, 5·6—35·6), and the UK (21·8%, 6·1—37·7).
Assuming independence, the combined worldwide PAR for the seven risk factors was 49·4% (95% CI 25·7—68·4), which equates to 16·8 million attributable cases (95% CI 8·7—23·2 million) of 33·9 million cases. However, after adjustment for the association between the risk factors, the estimate reduced to 28·2% (95% CI 14·2—41·5), which equates to 9·6 million attributable cases (95% CI 4·8—14·1 million) of 33·9 million cases.
Combined PAR estimates were about 30% for the USA, Europe, and the UK. Assuming a causal relation and intervention at the correct age for prevention, relative reductions of 10% per decade in the prevalence of each of the seven risk factors could reduce the prevalence of Alzheimer's disease in 2050 by 8·3% worldwide.
Assuming independence, the combined worldwide PAR for the seven risk factors was 49·4% (95% CI 25·7—68·4), which equates to 16·8 million attributable cases (95% CI 8·7—23·2 million) of 33·9 million cases. However, after adjustment for the association between the risk factors, the estimate reduced to 28·2% (95% CI 14·2—41·5), which equates to 9·6 million attributable cases (95% CI 4·8—14·1 million) of 33·9 million cases.
Combined PAR estimates were about 30% for the USA, Europe, and the UK. Assuming a causal relation and intervention at the correct age for prevention, relative reductions of 10% per decade in the prevalence of each of the seven risk factors could reduce the prevalence of Alzheimer's disease in 2050 by 8·3% worldwide.
Interpretation
After accounting for non-independence between risk factors, around a third of Alzheimer's diseases cases worldwide might be attributable to potentially modifiable risk factors.
Alzheimer's disease incidence might be reduced through improved access to education and use of effective methods targeted at reducing the prevalence of vascular risk factors (eg, physical inactivity, smoking, midlife hypertension, midlife obesity, and diabetes) and depression.
Alzheimer's disease incidence might be reduced through improved access to education and use of effective methods targeted at reducing the prevalence of vascular risk factors (eg, physical inactivity, smoking, midlife hypertension, midlife obesity, and diabetes) and depression.
FAB RESEARCH COMMENT:
These new calculations suggest that one third of dementia cases could be avoided by reducing known 'modifiable' risk factors. This estimate is lower than earlier ones (which suggested that half of all dementia cases might be preventable), because the researchers took account of the significant overlaps between many of these risk factors.Worldwide, these new analyses showed that lack of education makes the single biggest modifiable contribution to dementia - while in the US and UK, it is lack of exercise - followed by other cardiovascular risk factors in middle age, including high blood pressure, obesity, and diabetes - and also depression.
Noticeably absent from this list is any mention of NUTRITION or DIET - despite their fundamental importance as a contributory risk factor for obesity, Type 2 diabetes, high blood pressure - and the mounting evidence that nutritional interventions can reduce symptoms of depression, and also slow the progression of age-related cognitive decline and dementia.
For the related news item and additional FAB comment, see:
And for more information on the links between diet and dementia, as well as other age-related mental health problems, please see the following lists of articles, which are regularly updated.
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