About two in ten people over the age of 65 have mild cognitive impairment – a noticeable change in their memory, problem-solving abilities or attention. This is caused, in part, by the same brain changes that occur in dementia. While mild cognitive impairment often has little effect on a person’s way of living, 5-10% of people with it will develop dementia.
Why some people with mild cognitive impairment develop dementia while others don’t has long been a mystery. But a recent study from Columbia University has identified several factors that determine whether a person is more or less likely to develop mild cognitive impairment. These findings might give us a clue about who might be more likely to develop dementia.
The researchers looked at 2,903 people aged 65 or over and tracked their brain function for nine years. Cognitive impairment was diagnosed by looking at whether participants struggled with a memory task, if they reported difficulty performing certain daily tasks (such as using the phone) and hadn’t been diagnosed with dementia.
At the start of the study, all participants had normal brain function. At the six-year follow-up, 1,805 participants had normal cognitive function, 752 had mild cognitive impairment, and 301 had dementia. The researchers then followed up with the cognitively impaired group for another three years.
As some participants were “lost to follow-up” due to death, the researchers were only able to look at 480 people from the original mild cognitive impairment group. While 142 still had mild cognitive impairment, they found that 62 people from this group now had dementia. The researchers also found that 276 people no longer met the criteria for mild cognitive impairment – showing us that mild cognitive impairment does not always lead to dementia and it isn’t necessarily permanent.
Let’s first look at the factors linked to a lower risk of developing mild cognitive impairment.
The time a person spent in education was one factor that decreased a person’s risk of mild cognitive impairment. People who had an average of 11.5 years in education were 5% less likely to develop mild cognitive impairment compared with those with only ten years in education. The study did not differentiate between the type of education (such as school or higher education).
One theory for this link is because a longer time in education is linked to higher socioeconomic status – which may mean a person has better access to a healthier lifestyle and better healthcare.
Another theory is that education helps the brain build more neurons and connections, which helps the brain maintain good function. This may help the brain compensate for any changes that may happen as a result of mild cognitive impairment, such as memory loss.
People who were more physically active or social had a slightly lower risk of developing mild cognitive impairment.
To measure how social or active participants were, they filled out a questionnaire about the activities they did and how often they did them, such as walking or going to the movies. Researchers then gave participants a score out of 13. The higher the score, the more active the participant was. Those who didn’t have mild cognitive impairment scored 7.5 on average, while those who had mild cognitive impairment scored slightly lower at 7.4. People with dementia scored 5.8.
Previous studies have also shown that moderate-intensity activity (such as swimming) during mid-life or late-life can reduce the risk of mild cognitive impairment. The protective effect of exercise could be explained by beneficial structural changes that happen in our brains as a result of exercise. Growing evidence also shows us that being social can help maintain brain health and lower the risk of premature death.
Alzheimer’s: exercise may reduce brain inflammation, helping to protect us from the disease
People who had an income greater than US$36,000 (£27,264) a year had a 20% lower chance of developing mild cognitive impairment compared with those who made less than US$9,000 a year.
Income is probably linked to a lower risk of cognitive impairment for similar reasons as education, since people with a higher income are more likely to be able to afford better healthcare and afford a better diet and lifestyle. They may also live in areas where environmental factors – such as pollution – have less effect on them. This is important, as growing evidence shows pollution may also be linked to conditions such as Alzheimer’s and Parkinson’s disease.
The Columbia University researchers also identified several factors that were associated with a greater risk of developing mild cognitive impairment. They include:
The presence of the AP0E E4 allele (one of two or more versions of a gene) was found to increase the risk of developing mild cognitive impairment by 18%. This finding chimes with previous evidence which also shows that this allele can increase the risk of dementia.
People with AP0E E4 are around three times more likely to develop Alzheimer’s disease than those with a different variant of the AP0E gene. It’s thought this is because this variant makes people more likely to accumulate toxic protein deposits in the brain – a hallmark of Alzheimer’s disease. Researchers also think this gene only causes harm in older age.
Underlying health conditions
People with one or more chronic health conditions, such as heart disease, depression or diabetes, have a 9% greater risk of developing mild cognitive impairment, the Columbia University researchers found.
The increased burden of having several health conditions might mean a person engages less in their usual daily activities or social life. Both of these can accelerate a decline in brain health. Other conditions, such as heart disease, are also known to increase the risk of cognitive decline.
This study reminds us that mild cognitive impairment isn’t necessarily a prelude to dementia. In fact, some participants in the study who had mild cognitive impairment ended up returning to normal brain function. It’s not entirely certain why, but it could be down to lifestyle changes after diagnosis (such as exercising more) which may have improved outcomes. While it could also be the case that some participants were misdiagnosed at the beginning of the study, this is unlikely given the wide range of tools they used to confirm their diagnoses.
Our brains are dynamic and keeping them active throughout our lives is important to maintaining good brain function. While there are some risk factors – such as our genes – that we can’t change, keeping active and following and healthy lifestyle may be one way to lower our risk of mild cognitive impairment and dementia.
Mark Dallas receives funding from Alzheimer's Research UK and the Alzheimer's Association.