Tuesday June 9 2009
Exercise has many health benefits
The Daily Mail has reported that scientists have found four key factors that could prevent cognitive decline in old age. It said that exercise, education, social activity and not smoking are all part of the “recipe for staying sharp”. According to the newspaper, an eight-year study of 2,500 men and women, aged 70 to 79, found that these factors helped maintain mental performance.
The newspaper article is based on a relatively large study, which identified some differences between people who maintained their cognitive abilities in old age and those who did not. The study only included those who were functioning well at ages 70 to 79 and may not be representative of those who are not functioning well at this age. As with all studies of this type, it is difficult to be certain that the factors identified are themselves responsible for the differences in cognitive decline. However, doing exercise, taking part in social activities and not smoking are likely to have a number of benefits and older people should be encouraged to engage in these behaviours where possible.
Where did the story come from?
The research was carried out by Dr K Yaffe and colleagues from the University of California and other research centres in the US. The study was funded by the National Institutes of Health and National Institute on Aging, as well as various other sources including the Canadian Institutes of Health Research. The study was published in the peer-reviewed medical journal Neurology.
What kind of scientific study was this?
In this prospective cohort study, the researchers investigated the factors that could predict whether an individual would maintain their cognitive function in old age.
The current analysis looked at individuals enrolled in the Health, Aging and Body Composition (Health ABC) study. This study randomly sampled “well functioning” black and white people aged 70 to 79 who were living in Memphis and Pittsburgh, USA, in 1997. By well functioning, the researchers meant that the participants reported no difficulties walking a quarter of a mile, climbing 10 steps without resting or with the normal activity of daily living. They excluded anyone who had been diagnosed with life-threatening cancer or who planned to move out of the area within the next three years. This left 3,075 people who agreed to participate in the study.
At the beginning of the study, the participants gave information about themselves and their lifestyles, including their education, whether they were working or volunteering, living alone or with someone, providing care for a spouse or child, whether they visited family or friends at least once a week and whether they felt the need for more social support. They also completed a literacy test and their levels of depressive symptoms were measured using a standard scale. Participants were asked to rate their health (from excellent to poor) and report whether they had high blood pressure, diabetes or a history of heart attack, stroke or mini-stroke. They also gave information about smoking, alcohol consumption and weekly exercise (particularly moderate to vigorous exercise such as aerobics, weight training or brisk walking). The participants provided blood samples, which were tested for levels of fats and sugar. The researchers determined which forms of the APOE gene the participants carried as one particular form of this gene, the E4 variant, increases the risk of Alzheimer’s disease.
Participants’ cognitive function was assessed using a standard test (the Modified Mini-Mental State Examination or 3MS) at the start of the study and two, four and seven years later. The test gives a score from 0 to 100, with a higher score indicating better cognitive function. Based on how these scores changed from the beginning of the study to the final visit, the participants were split into three groups. The first group consisted of those who maintained (or improved) their cognitive function. In the second group were those who had only minor decline in their cognitive function (less than one standard deviation below the mean change). In the third were those who had a major decline in their cognitive function (more than one standard deviation below the mean change).
The researchers only included those participants who did not already have clinically impaired cognitive function at the start of the study (those with scores of 80 or over on the 3MS test). They also excluded anyone for whom there was no first 3MS score and those who had only one 3MS score. This left 2,509 people for analysis.
The researchers used the information they gathered to investigate whether individual characteristics predicted how cognitive function changed over time. When looking at each characteristic they took into account all other characteristics that were found to have an effect.
What were the results of the study?
Over the course of the study, 30% of the participants (758 people) maintained or improved their cognitive function, 53% (1,340 people) had a minor decline and 16% (411 people) had a major decline. Those who maintained their cognitive function had an average improvement of about one point on the 3MS test (score range 0 to 100), while minor decliners decreased by two points on average and major decliners by 9 points on average.
The researchers found that the characteristics that increased the likelihood of falling into the group that maintained their cognitive function (rather than having a minor decline) were: being younger, being white, having education to high-school level or higher, taking part in weekly moderate to vigorous exercise, not smoking and having a ninth grade (age 14 and 15) or higher literacy level.
They found that the characteristics that increased the likelihood of falling into the group that only had a minor decline in their cognitive function (rather than having a major decline) were: being younger, having education to high school level or higher, having a ninth grade or higher literacy level, having a higher level of social support and not having a copy of the E4 variant of the APOE gene.
What interpretations did the researchers draw from these results?
The researchers concluded that older people who maintain their cognitive function over time have different characteristics to those who experience minor decline in cognitive function. Some of the characteristics are modifiable and could be targeted in “prevention programs to promote successful cognitive aging”.
What does the NHS Knowledge Service make of this study?
The study’s strengths are that it followed individuals up over time and that it was relatively large. The researchers managed to define cognitive groups based on the participants’ rate of cognitive change over several years, which allowed them to distinguish between people with major decline (possibly a warning of dementia) and the more normal rate of age-related decline. There are a number of points to note when interpreting the results:
- The factors that were linked with different patterns of cognitive decline may not themselves be responsible. There may be other, unknown characteristics (confounders) that affect the results, such as socioeconomic status or diet.
- Although some of the factors may be modifiable, such as exercise, this does not necessarily mean that doing more exercise will prevent cognitive decline. To determine whether this is the case would ideally require randomised controlled trials, which is probably not feasible.
- The participants submitted most of their health information themselves, for example whether they had high blood pressure or diabetes, and there may have been some inaccuracies in these reports.
- Only current behaviours, such as smoking, alcohol consumption and exercise, were assessed, and these may not have been representative of the individual’s habits in the past.
- The study included older people who were functioning well after 70 years and so the results may not apply to older people who are functioning less well. People who are healthy and functioning well at this age may be more likely to maintain their cognitive function over time than the general population, which will also include people who are not healthy or functioning well.
The findings of this study support the idea that both environmental and genetic factors may play a role in change in cognitive function with age. It also suggests that slightly different factors may be involved in maintaining cognitive function and in determining whether any decline is major or minor.
With the exception of the participants’ access to social support, the study did not identify any modifiable factors in older people that decided whether they had either major or minor decline in cognitive function. In addition, there was a particularly strong link between major decline and the E4 variant of the APOE gene.
However, the study suggests that certain modifiable lifestyle choices that older people make, namely partaking in exercise and not smoking, may increase their likelihood of maintaining their cognitive abilities rather than experiencing a decline. These lifestyle choices have other health benefits and should be encouraged where possible.