Healthy lifestyle reduces dementia risk even in those with genetic risk factors

"Bad dementia genes can be overcome through healthy living, study finds," reports The Daily Telegraph.

The newspaper reports that regular exercise, not smoking, drinking sensibly, and eating a healthy diet have been found to reduce risk of getting dementia even if a person has a higher genetic risk of developing the condition.

This news is based on an analysis of data collected over 8 years from almost 200,000 adults aged 60 and over in the UK. The volunteers completed questionnaires at the start of the study about their lifestyles, and researchers looked at their DNA to see who carried genetic variations that have been associated with increased risk of Alzheimer's – the most common type of dementia.

The researchers found that among participants who had a higher genetic risk of getting dementia, only about 11 in every 1,000 with healthier lifestyles developed the condition during follow-up, compared with about 18 in every 1,000 with unhealthy lifestyles.

There are some limitations to the study. For example, some cases of dementia are likely to have been missed as researchers did not directly assess the participants, instead relying on hospital inpatient records and death certificates.

Overall, however, the findings are good news. We cannot change our genetics, but this study suggests that regardless of this, changing our lifestyles could help everyone reduce their dementia risk.

Read more about how healthy lifestyle choices may help reduce your risk of dementia.

Where did the story come from?

This study was conducted by researchers from the UK (University of Exeter Medical School, University of Oxford, University College London, The Alan Turing Institute), the US (University of Michigan, Veterans Affairs Center for Clinical Management Research in Michigan), Australia (University of South Australia) and Germany (University of Hamburg, Hamburg Center for Health Economics).

The study was published in the peer-reviewed Journal of American Medical Association). The paper is open-access, meaning it can be accessed for free online.

The UK media generally reports this study reasonably well. BBC News gives a good account of the study, and reports the actual numbers of people in the different groups developing the condition, which helps to put the findings into context. The Guardian also includes a description of some of the limitations to the study, which gives balance.

Some of the reports oversimplify the results. For example, the Daily Mirror's headline suggests that protecting against dementia is "all in your diet", when in fact smoking, physical activity, and alcohol consumption also play a role. They do clarify this later in the article.

What kind of research was this?

This was a cohort study that looked at whether older people who had healthier lifestyles were less likely to get dementia, particularly among those whose genetics made them more likely to develop the condition.

There are various different types of dementia, the most common being Alzheimer's disease and vascular dementia. The causes of dementia are not fully understood, and they are likely to differ to some extent between the different forms. We do know that genetics has some influence, with many genes likely to play a role in most forms of dementia.

There is also evidence that lifestyle behaviours play a role. This is the case in vascular dementia, which has similar risk factors to heart disease as it's caused by a reduced blood supply to the brain, but also applies to other types of dementia such as Alzheimer's.

People who have healthy diets, are physically active, do not smoke and only drink alcohol in moderation are at lower risk of developing dementia.

We do not fully understand how genetics and lifestyle risk interact with each other to affect dementia risk. In this study, the researchers mainly wanted to see whether having a healthy lifestyle reduced risk in people who had genetic risk factors for dementia. Previous studies that have looked at this question were too small to be conclusive.

This type of study is the most feasible way of looking at this type of question, as randomly assigning people to risky lifestyle activities, such as smoking, would not be ethical.

What did the research involve?

The researchers used data that was collected by the UK Biobank, which is an ongoing programme following the health and wellbeing of over half a million volunteers. They analysed the data from 196,383 adults aged 60 or over who did not have memory or thinking problems (cognitive impairment) or dementia when they were recruited, and who had provided DNA samples.

The researchers analysed the DNA of the participants to see if they carried almost 250,000 single “letter” genetic variations that have been found to be associated with increased risk of developing Alzheimer's disease. These variants are known as single nucleotide polymorphisms or SNPs.

They used this information to give each person a "genetic risk score". Those with the highest 20% of risk scores were classed as being at "high genetic risk", while those with the lowest 20% of risk scores were classed as being at "low genetic risk".

When they were recruited for the Biobank, participants completed online questionnaires about their lifestyles.

In the current study, the researchers assessed 4 behaviours that affect dementia risk – smoking, alcohol consumption, diet and physical activity.

Healthy behaviours were considered to be:

• Not currently smoking.
• Being regularly physically active (at least 150 minutes of moderate activity or 75 minutes of vigorous activity a week; or taking moderate physical activity at least 5 days a week or vigorous activity once a week).
• Healthy diet (at least 3 servings a day of fruits, vegetables and wholegrains; at least 2 servings of fish a week, less than 1 serving of processed meats a week, and no more than 1.5 servings of unprocessed red meats or refined grains a week)
• Moderate alcohol consumption – up to 14 grams of alcohol (1.75 units) a day for women and up to 28 grams (3.5 units) a day for men.

The researchers calculated a "weighted lifestyle score" ranging from 0 to 100 based on how many of the healthy behaviours a person had, and how strongly each of the behaviours was linked with dementia in their analyses.

They classed people with the highest scores (74 to 100 points) as having a favourable or "healthy" lifestyle, and those with the lowest scores (0 to 51 points) with an unfavourable or "unhealthy" lifestyle.

The researchers identified people who had developed any form of dementia during the study using hospital inpatient records and death records. They carried out statistical analyses to look at the risk of developing dementia in those with different levels of genetic risk, and whether this varied according to their lifestyle scores.

They took into account factors that could influence the results, such as:

• age
• gender
• education level
• socioeconomic status

What were the basic results?

The researchers classed about two-thirds of participants (68%) as having a healthy lifestyle, 8% as having an unhealthy lifestyle, and the remainder (24%) in between. On average, participants were followed up for 8 years after they were recruited to take part.

During follow-up, 1,769 participants (0.9%) developed dementia. The types of dementia the participants had were not reported. Among those with high genetic risk, 1.2% developed dementia, compared with 0.6% of those with low genetic risk. Among those classed as having an unhealthy lifestyle, 1.2% developed dementia, compared with 0.8% of those with a healthy lifestyle.

Even among participants with a high genetic risk, those with a healthy lifestyle were less likely to develop dementia. About 1.1% of those with a high genetic risk but a healthy lifestyle developed dementia, compared to about 1.8% of those with high genetic risk and an unhealthy lifestyle.

This represented about a 32% reduction in risk of developing dementia during follow-up (hazard ratio [HR] 0.68, 95% confidence interval [CI] 0.51 to 0.90).

How did the researchers interpret the results?

The researchers concluded that in older adults having a healthy lifestyle was associated with lower dementia risk, even among those whose genetics put them at higher risk.

Conclusion

This large UK cohort study has suggested that a healthy lifestyle can reduce overall dementia risk, even in people with genetic risk factors for Alzheimer's disease.

There are some limitations to be aware of. First, the analysis only included European people, which means the results may not apply to people of other ethnicities. The study also relied on volunteers, so the participants may not be representative of the whole population. For example, those who volunteer may be healthier, better educated or of a higher socioeconomic status.

The data on lifestyle was only collected at the start of the study, and may not have accurately represented the participants' behaviours over their lifetime. Data on dementia diagnoses relied on hospital inpatient data and data from death certificates. However, at least some of those with dementia may not have received inpatient care for any cause, and therefore would not have been identified as having dementia in the analyses.

The study looked at genetic risk factors for Alzheimer's disease, but not at the outcome of developing any type of dementia. This may be because Alzheimer's is the most common form of dementia, and probably the best studied. Analysing results by type of dementia would have been useful, but given that only relatively few people developed dementia, may not have been feasible.

As with all studies of this type, we cannot be sure that healthy lifestyle is definitely the only factor contributing to the differences in risk. Other unmeasured environmental factors may also play a role.

The positive message of this study is that even those with some genetic predisposition to developing dementia can still do something about it. It may also be of some comfort to bear in mind that even among those with high genetic risk in this study, only 1.2% developed dementia during follow-up. While this may in part be due to the fact that participants were still not very old at the end of the study (average age 72 years), it still shows that genetic risk factors are not a guarantee of a diagnosis.

Overall, the results of this study do offer reassurance that having a healthy lifestyle is your best chance of reducing your dementia risk.