Personality and dementia risk

“Being laid-back and outgoing makes you 50% less likely to develop Alzheimer's disease”, the Daily Mail reported. The newspaper said that people who are anxious, shy and prone to stress are more likely to go on to develop dementia. It said a study looked at the personalities and lifestyles of 506 older people and followed them for six years. Those who were calm had a 50% lower risk of dementia, even if they were not socially active, than those who were isolated and prone to stress.

This study found that people with low levels of neuroticism and high levels of extroversion (calm, relaxed types with outgoing personalities) had less risk of dementia than those with high neuroticism (those prone to distress and poor coping responses) and high extroversion.

However, the study cannot prove that these personality factors themselves affected the risk of dementia, as early dementia-related changes could themselves have affected personality. This study has not looked at whether changing your personality, which may not be possible, can affect your risk of dementia. For elderly people, maintaining social contact with others is likely to have benefits, but whether or not it reduces dementia risk remains to be proven.

Where did the story come from?

Dr Hui-Xin Wang and colleagues from the Karolinska Institutet and other research institutes in Sweden and the US carried out this research. The work was funded by the Swedish Council for Working Life and Social Research, and various other charitable organisations in Sweden and the US. The study was published in the peer-reviewed medical journal: Neurology.

What kind of scientific study was this?

This prospective cohort study looked at the relationship between personality traits (neuroticism and extroversion), lifestyle and dementia. Previous studies have found that stress is associated with degenerative changes in the brain. It has also been found that people’s personality traits and their level of social interaction may affect their ability to cope with stress. Therefore, the researchers wanted to investigate whether these factors might affect risk of dementia, which is a result of degenerative changes in the brain.

The participants were obtained from a previous cohort study of ageing and dementia in Sweden. The researchers excluded anyone from that study who met criteria for probable dementia at the time of assessment, and those who were unable to complete a personality questionnaire that assessed neuroticism and extroversion. This neuroticism part of the questionnaire is designed to identify people prone to ‘psychological distress, unrealistic ideas, excessive cravings or urges, and maladaptive coping responses’. Low scores indicate people to be ‘calmer, more relaxed, unemotional, and self-satisfied’. The extroversion part of the questionnaire assesses ‘quantity and intensity of interpersonal interaction, activity level, need for stimulation, and capacity for joy’. People who score lower on extraversion are identified as being ‘more reserved, sober, task-oriented, and quiet’.
Those who met inclusion criteria were asked to take part in a personal interview in which they were asked about their lifestyle, including their social interactions and leisure activities.

Of the people who were asked, 544 completed the questionnaire, and 506 (average age 83 years) were successfully followed up for an average of six years. The participants were given a full clinical assessment at three and six years, including medical history and psychological assessment. If an individual could not answer questions, the researchers identified a person close to them who could provide the relevant information.

Diagnoses of dementia were based on standard criteria. Two physicians made independent diagnoses, and if they agreed then this was the final diagnosis. If they disagreed then a third opinion was obtained. If a person died, their medical history and diagnoses were assessed using hospital records and death certificates.

The researchers then looked at whether levels of neuroticism or extroversion were individually associated with dementia. They also looked at the effects of these two personality traits together, and at how this association was affected by social interaction. They compared the proportion of people who developed dementia among those with low levels of neuroticism, extroversion or both with those who had high levels of both. The researchers adjusted their analyses for factors that could affect the results, such as whether the participants had the  form of the ApoE gene which has been associated with a higher risk of Alzheimer’s disease. They also took into account the participants’ age, cognitive function, gender, level of education, depressive symptoms or diagnoses, vascular disease, and whether they had died or were still alive at follow up.

What were the results of the study?

Of the 506 participants, 144 (28%) developed dementia during the six years of follow up. When they looked at each personality trait individually, the researchers found no association between the participants’ neuroticism or extroversion and their risk of developing dementia. However, when the two traits were assessed together some associations with dementia were found. People who had low neuroticism but high extroversion were about half as likely to develop dementia as those with high neuroticism and high extroversion (hazard ratio 0.51, 95% CI 0.28 to 0.94). Risk of dementia among people with low neuroticism and extroversion, or high neuroticism and low extroversion did not differ from those with high levels of both traits.

The researchers then split the participants into those with different social lifestyles. Among those who had an inactive and socially isolated lifestyle, people who were less neurotic  had a lower risk of dementia than those who were more neurotic, but this was not the case among people with an active and socially integrated lifestyle. Extroversion was not associated with risk of dementia in either socially inactive or socially integrated groups.

What interpretations did the researchers draw from these results?

The researchers concluded that people with low neuroticism and high extroversion have the lowest risk of dementia. They say that low neuroticism alone can reduce the risk of dementia in people with an inactive and socially isolated lifestyle.

What does the NHS Knowledge Service make of this study?

The prospective design of this study is one of its strengths; however, there are some limitations to consider:

• Even though this study followed people over time, it is difficult to determine the sequence of events. People who did not have detectable dementia may have had very early brain changes associated with this condition, and these changes may have affected their personality rather than the other way around. However, the authors feel they reduced this possibility by testing for cognitive performance at the beginning of the study, and adjusting their analyses accordingly.
• Even if the personality traits preceded the brain changes, it does not necessarily mean that the personality traits themselves increased the risk of dementia. There may be another factor or factors that affect both personality and risk of dementia.
• About a third of the people asked did not complete the personality questionnaire, and this may have affected the results if they differed from those who chose to complete it.
• Personality was only assessed once, and may not have been indicative of personality at other times during the participants’ lives.
• It is not possible to say from this study whether attempting to change one’s social life would have an effect on risk of dementia.
• The results may not be applicable to other countries, where social customs and interactions may differ.

Further replication of the findings of this study in other settings would increase confidence in the results. By objectively measuring dementia over time, by using a series of brain scans for example, it may be possible to avoid the criticism that this study is a “chicken and egg scenario”. These could help to determine whether it is the personality traits that increase the risk of dementia or if they are simply an early sign of the disease.