Does exercise prevent dementia?

"Taking exercise just three times a week in middle age can help improve the memory and may ward off the start of dementia," reported the Daily Express . It said that a study has found that people who did regular moderate aerobic exercise for one year showed increases in the size of their hippocampus, an area of the brain related to memory.

This study was in people aged 55 to 80, comparing the size of the hippocampus on MRI scans and their ability in memory tests following a year of either aerobic exercise or light exercise, including non-aerobic toning exercises and yoga. The aerobic exercise group showed small increases in hippocampal volume compared with the control group, which showed small decreases in volume.

However, these size differences did not translate into differences in memory faculties between the groups. Although the aerobic exercise group’s memories did improve over this time, the improvements were not significantly different from that of the control group, which also showed small improvements. This may indicate that any type of exercise leads to improvements in memory, including non-aerobic toning exercises and yoga, but further research would need to clarify this. In the meantime, physical fitness is associated with many other physical and mental benefits.

Where did the story come from?

The study was carried out by researchers from several universities in the USA. It was funded by the National Institute on Aging and the National Institutes of Health. The study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences .

What kind of research was this?

This randomised controlled trial tested the theory that aerobic exercise can increase the size of the hippocampus in older adults, leading to improvements in spatial memory. The hippocampus is an area of the brain responsible for long-term memory and spatial navigation.

The researchers said that the hippocampus shrinks in late adulthood, leading to memory impairment and an increased risk of dementia. They said that studies have shown that hippocampal volume is associated with physical fitness, and efforts are now being made to find strategies to prevent the hippocampus from shrinking.

What did the research involve?

The researchers enrolled older adults (between the ages of 55 and 80) from the community. The researchers excluded anyone diagnosed with depression (measured by a standard diagnostic scale) or a history of neurological or cardiovascular disease. Originally there were 179 people in the study, but some dropped out or were excluded, so only 120 (82.7%) were included in the final analyses.

At the start of the study, all the participants had their aerobic fitness levels tested, MRI scans taken of their brains, and completed standard memory tests. Blood tests were also taken to measure levels of brain-derived neurotrophic factor (BDNF), a protein in the brain thought to be important for long-term memory.

The participants were then randomised to either an aerobic walking group or a control group, both supervised by trained exercise instructors. People in the aerobic exercise group increased their exercise levels over the first seven weeks until they were walking 40 minutes a day, three times a week. They were encouraged to walk at moderate intensity, measured in relation to individual heart rate (the target heart rate zone was calculated according to resting and maximum heart rates achieved during a baseline exercise test). Those in the control group did regular stretching exercises, lightweight training and yoga. Both groups completed exercise logs regularly.

The participants all had further brain scans, blood (BDNF) tests, memory tests and fitness tests at six months, and again after the completion of the intervention, at one year. The researchers used standard statistical methods to analyse their results.

What were the basic results?

The researchers found that after one year:

• The MRI scans showed that people in the aerobic exercise group had increases in the size of their hippocampus (by 2.12% in the left hippocampus and 1.97% in the right). In the control group, hippocampus size declined by 1.40% and 1.43% respectively.
• Most of the increase in size took place in the anterior (front) hippocampus, with minimal change in size in the posterior area or other regions of the brain. (The researchers point out that cells in the anterior hippocampus are involved in spatial memory and also show more age-related atrophy than those in the posterior).
• The exercise group had improved aerobic fitness levels, with a 7.78% improvement in maximal oxygen consumption (called VO2 max) compared with a 1.11% improvement in the control group.
• There were no differences in memory improvements between the two groups.
• There was no difference between the groups in levels of BDNF.

Further analyses within or across the two groups showed that:

• Greater improvements in aerobic fitness were associated with greater increases in hippocampal volume.
• However, changes in aerobic fitness from the start of the study were not associated with memory improvements in either group.
• In the aerobic exercise group, increases in levels of BDNF correlated with a greater increase in hippocampus volume.
• In the aerobic exercise group, increased hippocampal volume was associated with improvement in memory tests, when measured against performance at the start of the study.

How did the researchers interpret the results?

The researchers said their “theoretically important findings” indicate that one year of aerobic training is effective at reversing hippocampal volume loss in late adulthood, and that this “translates to” improved memory function.

Conclusion

This study found that introducing moderate intensity exercise for one year to a group of older people led to an increase in the size of an area in their brains associated with long-term memory (posterior hippocampus). This was compared with people in the control group (who took part in regular stretching exercises, lightweight training and yoga), who were found to have a small decrease in hippocampal volume.

However, these differences in sizes of areas of the brain did not translate into differences in memory faculties between the groups. Although the aerobic exercise group’s memories did improve over this time, the improvements were not significantly different from that of the control group, which also showed improvements. This may indicate that any type of exercise may cause improvements in memory, including non-aerobic toning exercises and yoga.

This was a well-designed randomised controlled trial, the “gold standard” for looking at the effectiveness of an intervention (in this case aerobic exercise). However, the findings demonstrating a possible association between aerobic exercise and memory improvement are from analyses that were not part of the original trial design, and did not compare the intervention group with that of the control group. As such, these findings cannot be judged to be as reliable as they would have been had they been planned from the start of the study.

It is also important to note that the small size of the study, which was conducted over a short time period and did not take account other factors that might affect memory, such as stress or alcohol intake. Although the participants were free of neurological illness at the start of the study it is possible this could have developed within the study timeframe and affected both brain size and memory.

Due to these shortcomings, this analysis cannot prove that aerobic exercise improves memory, and further research is required. However, physical fitness is associated with many other physical and mental benefits at all ages.