Risk factors for dementia: separating facts from myths

Risk factors for dementia: separating the facts from the myths

Nov 12 2014

The world is going through a period of increasing public awareness of dementia, with many countries promising to ‘tackle’ the disease.

By next year, there will be 850,000 people living with dementia in the UK and, if current trends continue, the number of people in the UK with dementia is forecast to increase by 40% over the next 12 years and by 156% over the next 38 years.

Dementia currently costs the UK £26 billion a year, so this cost is only set to increase along with the prevalence (Prince et al, Dementia UK, 2014).

With no known cure, the importance of treatment strategies reducing the risk or delaying the onset of dementia has become a high priority.

Methods

The World Alzheimer Report 2014 (Prince et al, World Alzheimer Report, 2014) aimed to examine all evidence regarding protective and modifiable risk factors for dementia and those interventions trialled for modifying them. The comprehensive report consists of 104 pages, so here I’ve summarised their findings, with the aim of communicating them more succinctly for everyone out there in the woodland.

Dementia myths are commonplace, so we’ve digested the report and separated the fact from the fiction.

Non-modifiable risk factors

MYTHS	FACTS
Everyone gets dementia if they live long enough. Dementia is not a normal part of ageing.	APOE gene E4 allele increases the risk of dementia. The genotype is neither necessary nor sufficient to cause dementia, but does increase risk.
	You are more likely to get dementia as you get older.

Developmental risk factors

MYTHS	FACTS
We couldn’t find any in the report. If you can think of some, please share them with us in the comments section below.	Dementia risk is increased by inadequate nutrition in early life (indicated by a shorter leg length or smaller head circumference). There is limited but consistent evidence supporting this association.
	Dementia risk is increased in people who experience stressful events in early life. The most studied risk was parental death, however, this evidence comes from only three studies, two of which relied on self-reporting and could be subject to recall bias.
	Education is protective against dementia. Meta-analysis showed a reduction in risk from a high educational level to be around 40%.

Psychological and psychosocial risk factors

MYTHS	FACTS
Anxiety increases the risk of dementia. At least for now this remains a myth, with not enough evidence supporting a link, but it is worth keeping in mind the comorbidity with depression.	Depression increases the risk of dementia. Depression is estimated to almost double the risk of dementia, but results do not provide evidence to suggest whether depression is a prodrome of dementia or an independent causal risk factor.
Sleep disorders increase the risk of dementia. Although sleep disturbance can be common in those with dementia, there is very little evidence to support this being an independent risk factor. Keep in mind confounding factors such as sleeping pills and depression.	Your personality type can increase the risk of dementia. Different personality types alter the tendency to experience negative emotions and psychological distress, with one large systematic review showing those with high levels of neuroticism having a 32% higher risk for Alzheimer’s disease. Despite these findings, there is insufficient evidence to support interventions targeting psychological distress.

Lifestyle risk factors

MYTHS	FACTS
Ex-smokers still carry a higher risk of dementia. Ex-smokers are at a similar risk as those who have never smoked.	Smoking increases risk of dementia. It is well known that smoking increases the risk of stroke and therefore vascular dementia, but the systematic review and meta-analyses within the report show an increased risk of Alzheimer’s disease with smoking, with a non-significant trend in the same direction for any dementia.
Alcohol increases risk of dementia. Meta-analysis showed alcohol can actually have neuroprotective effects. Compared to non-drinkers, moderate drinkers were found to have a lower risk of Alzheimer’s disease (RR 0.62) and any dementia (RR 0.54). Heavy/excessive drinkers were found to have similar risk compared to non-drinkers. However, these should not be taken as reassuring results and the other detrimental health effects of alcohol should not be forgotten when giving lifestyle advice.	Physical activity reduces risk of dementia. Some studies suggest a reduction of up to 40% in risk for those undertaking physical activity, but studies with longer follow-up periods reported consistently negative results. For this reason, physical activity is not yet proven to be an effective way to prevent or delay the onset of dementia. However, the positive effects of physical activity on health, such as vascular risk factors and diseases, should be held in mind, as these are in turn related to dementia.
Drinking wine reduces your risk of dementia. Similar risks were found between those who only drank wine compared to non-drinkers.	Cognitive stimulation delays the onset of dementia. Evidence suggests that cognitive activity in late-life may be beneficial for both brain structure and function, although the exact type of cognitive stimulation warrants further research.
Dietary changes can alter the risk of dementia. Studies examining the effects of B vitamins, antioxidants, omega-3 and Mediterranean diet showed some positive results, but overall these findings have not been consistently replicated.

Cardiovascular risk factors

MYTHS	FACTS
Obesity increases the risk of dementia. Evidence does not support a direct association, but it is important to remember the detrimental physical health effects of obesity.	Hypertension increases the risk of dementia. Strong and consistent evidence links hypertension with any type of dementia, specifically in those who have midlife hypertension.
Everyone should be given statins to reduce the risk of dementia. Although, as above, there is a proven link between high cholesterol and dementia risk, the evidence to date does not support the hypothesis that preventing or treating dyslipidaemia will help to prevent cognitive decline, Alzheimer’s disease or other forms of dementia.	Cholesterol increases the risk of dementia. There is weak evidence to suggest an increased risk of dementia with high levels of midlife (but not late-life) total cholesterol. Interestingly, the most consistent finding across studies showed that a more rapid decline in total cholesterol from mid- to late-life predicts the onset of Alzheimer’s disease, although an explanation of the underlying mechanism currently escapes researchers.
	Diabetes increases the risk of dementia. There is a strong and consistent body of evidence to support the association between late-life diabetes and subsequent onset of dementia. Unsurprisingly, it is more strongly linked with vascular dementia than Alzheimer’s disease.

Limitations

Due to the large number of studies included in this report, some will always be stronger than others. However, the report authors have done their utmost to pool results and draw the most robust conclusions as possible.
With risk factors as prevalent as some of the ones studied here, it is inevitable that confounding will affect any study and this needs to be kept in mind when interpreting results.
Where possible, the report comments on risks for different types of dementia, although as we know, these conditions can have vastly different symptoms and affect different populations. Further research will be needed into the different types of dementia and the specific risk factors for them.

Conclusions

As the report dictates, “what is good for your heart is good for your brain”. All the advice you are used to giving about smoking, hypertension and diabetes apply to dementia as well. One of the things the World Alzheimer Report impresses upon the reader is that it’s never too late to change.

The strongest evidence for possible causal associations with dementia is:

Low education in early life
Hypertension
Smoking
Diabetes

Many of these risk factors do not necessitate new public health strategies and can be incorporated into those approaches already aimed at other conditions, particularly cardiovascular diseases.

The World Alzheimer Report authors used a large number of sources of evidence, from high quality journals and also conducted individual meta-analyses themselves for specific topics. They carefully considered both the existing evidence in-vitro for risk factors, as well as the real effect seen in the population.

Their key message essentially boils down to leading a healthy life, looking after your body as well as your mind, as you would do to reduce the risk of any other disease. Overall, this is an important report, which dispels some common myths and makes helpful suggestions for future research.