Tuesday April 24 2012
It is unclear whether exercise can halt cognitive decline
Exercise can dramatically alter the rate of mental decline in elderly people with early signs of dementia, the Daily Express reported today.
The news reports are based on a small study that compared how different types of exercise may affect the mental ability of elderly women with “probable” mild cognitive impairment (MCI). MCI is a risk factor for developing dementia, although it does not always lead to the condition. During a six-month trial, elderly women were asked to regularly perform either aerobic exercise, muscle-strengthening “resistance training” such as weightlifting, or classes involving gentle stretches and movement. Researchers found that women who performed resistance exercises showed improvements in several aspects of their cognitive functioning.
Elderly people are rightly advised to keep active, as it helps maintain physical health. However, whether exercise can prevent cognitive decline is less clear from these results. This small study did not show that resistance training cuts the risk of dementia, nor did it set out to do so. To investigate this, it would have needed to have followed participants over a longer period and assessed whether they met criteria for diagnosing dementia rather than MCI. Also, the women’s mental abilities were tested only twice, at the start of the study and after six months of exercise. Many factors may have affected how well they performed, including how they felt on the day of the tests.
This was a “proof-of-concept study”, which means it was designed to provide only preliminary evidence that exercise may have an effect on cognitive ability. The results are interesting, but further research is required.
Where did the story come from?
The study was carried out by researchers from a number of institutions, including the University of Vancouver in Canada and the University of Illinois in the US. It was funded by the Pacific Alzheimer’s Research Foundation. The study was published in the peer-reviewed journal Archives of Internal Medicine.
The Express’s claim that exercise cuts dementia risk was misleading, since the study did not take a long-term look at whether participants developed dementia. It only compared how people who were judged to “probably have” mild cognitive impairment (MCI) performed in mental tests after six months of different types of exercise. MCI does not necessarily progress to dementia, although it is a risk factor.
What kind of research was this?
This randomised controlled trial looked at whether different types of exercise improved mental ability in elderly women with memory problems. The two types of exercises researchers tested were:
- aerobic exercise – such as walking, jogging and swimming, which generally increase the heart rate and the oxygen available to the body
- resistance training – such as weightlifting, which increases muscle strength
Resistance training is usually “anaerobic”, which literally means “without air”. It uses muscles at high intensity for a short period.
The researchers say that exercise is a promising strategy for combating cognitive decline and that aerobic and resistance training have been shown to enhance mental performance both in healthy elderly people and in those with MCI. However, they say that no study has yet compared the effects of the two types of exercise on mental function in older people with MCI. Therefore, they set out to perform a “proof of concept” study to compare their potential effects. A proof of concept study is intended to provide preliminary evidence on a theory.
What did the research involve?
The study involved 86 women aged 70 to 80 years old who were living in the community (not in care or a home). It is not clear how they were recruited. They were randomly allocated to either twice-weekly resistance training sessions (28 women), twice-weekly aerobic training (30 women) or twice-weekly balance-and-tone sessions (28 women), the last being a control group to compare against the aerobic and resistance training groups. They were classified as having “probable” MCI according to their scores on a cognitive assessment scale and whether they reported memory problems.
At the start and end of the study, the women took several tests to measure cognitive function. The main one was the Stroop test, an established test in which the name of a colour is printed in a different colour (for example, the word "red" is printed in blue ink). Other tests examined memory and problem-solving ability. The women also underwent functional MRI (magnetic resonance imaging) scans of their brains while performing some memory tasks. This is a special type of MRI that looks at changes in blood flow as an indication of changes in brain activity. Researchers also gave tests to assess the general balance, mobility and cardiovascular capacity of participants.
The 60-minute fitness classes were led by certified fitness instructors. For resistance training, both free weights and a pneumatic exercise system were used. Participants did two sets of six to eight repetitions of each exercise, with loads being progressively increased. The aerobic exercise was an outdoor walking programme, with age-specific target heart rates. The control group exercise consisted of stretching, performing a range of motions, balance exercises and relaxation techniques.
What were the basic results?
Of the 86 participants, 77 completed the trial. The researchers reported that, compared with the control group, those performing resistance training showed significantly improved performance on the Stroop test and one memory task (associative memory). Compared with the control group, the resistance group also had greater changes in blood flow in certain areas of the brain when they were tested on their memory skills.
The aerobic training group significantly improved in general balance, mobility and cardiovascular capacity compared with the control group. No other differences in test results were found between the three groups.
Two women suffered shortness of breath and four had falls, although there were no significant differences in the rate of adverse events between the groups.
How did the researchers interpret the results?
The researchers said that, in older women with memory problems, six months of resistance training improved certain measures of cognitive function as well as patterns of brain activity during mental tests, compared with women in the control group. Aerobic exercise improved physical function. According to the researchers, this provides “new evidence” that resistance training can be of benefit in people at risk of dementia. Twice-weekly sessions of resistance training could be a promising strategy to “alter the trajectory of cognitive decline” in older people with MCI.
This was a “proof-of-concept study”, which means it was designed to provide only preliminary evidence that exercise may have an effect on cognitive ability. The results of this small, initial study are of interest, but further research is required.
Important points to consider include:
- The study appears to have tested mental ability only twice, at the start of the study and after six months of exercise. Many factors may have affected how well people performed, including how they felt on the day of the test.
- People in the study had only “probable” mild cognitive impairment. This was based on having a score below a threshold on a certain test (the Montreal Cognitive Assessment) and reporting memory problems. This is not a formal diagnosis of MCI, so it is not certain how many of the participants really had the condition.
- The trial only assessed performance on a variety of diagnostic tests. It did not set out to assess whether women met diagnostic criteria for dementia at the end of the study. As such, it cannot show that resistance training cuts the risk of dementia.
- It is not known how or whether the changes observed (such as improvements on the Stroop colour test and associative memory in the resistance training group) would have translated into noticeable improvements in daily life and functioning.
- The study only examined women.
While exercise is generally thought to be good for older people, further research is required to find out which type of exercise, if any, could help halt cognitive decline and reduce the risk of dementia.