Previous research has suggested that physical exercise can improve cognition in healthy older adults.
The findings of the new randomized controlled trials were presented at this year's Alzheimer's Association International Conference (AAIC) in Washington, D.C.
"Based on the results we heard reported today at AAIC 2015, exercise or regular physical activity might play a role in both protecting your brain from Alzheimer's disease and other dementias, and also living better with the disease if you have it," reports Maria Carrillo, chief science officer of the Alzheimer's Association.
Previously at the conference, researchers presented evidence that high television viewing and low levels of physical activity in early to mid-adulthood may raise the risk of poorer cognitive function later in life. These new studies suggest that, in turn, exercise could have wider benefits for the brain.
The first of the randomized controlled trials aimed to assess the effects of moderate to high-intensity exercise in 200 patients with mild to moderate Alzheimer's disease. Participants were assigned to either a group taking part in a supervised exercise program for 16 weeks or a control group.
Dr. Steen Hasselbalch and colleagues from the Danish Dementia Research Centre in Copenhagen, Denmark, found that the group following the exercise program experienced far fewer of the neuropsychiatric symptoms often occurring in Alzheimer's disease than the control group.
The researchers observed that the psychiatric symptoms of the control group - such as anxiety, irritability and depression - deteriorated while the symptoms of the participants in the exercise group improved slightly. In particular, participants attending 80% of exercise classes who exercised vigorously experienced significant improvements in their mental speed and attention.
"While our results need to be verified in larger and more diverse groups, the positive effects of exercise on these symptoms that we saw in our study may prove to be an effective complement or combination with antidementia drugs," reports Dr. Hasselbach. "This calls for further study of multimodal treatment strategies, including lifestyle and drug therapies."
Aerobic exercise found to reduce levels of tau protein
Another study investigated the impact of exercise on one of the physiological sides of Alzheimer's disease. People with the condition often develop brain lesions known as tau tangles, whereby the protein tau collapses into twisted strands, destroying a vital cell transport system and killing brain cells.
Higher levels of tau in the brain are associated with swifter decline to Alzheimer's dementia and, as a result, many researchers are concerned with trying to reduce tau as part of treatment to prevent dementia and cognitive decline.
Researchers from Wake Forest School of Medicine in Winston-Salem, NC, randomly assigned 65 sedentary adults with mild cognitive impairment to either a group receiving supervised aerobic training or a group that did stretching exercises four times a week.
After 6 months, they discovered that the aerobic exercise group had statistically significant reductions in tau levels compared with the stretching group. Aerobic exercise also improved blood flow in the regions of the brain associated with memory and processing, leading to corresponding improvements in attention, planning and executive function.
"These findings are important because they strongly suggest a potent lifestyle intervention such as aerobic exercise can impact Alzheimer's-related changes in the brain," says study co-author Laura Baker. "No currently approved medication can rival these effects."
Cognitive function improved in patients with vascular cognitive impairment
The final study examined how aerobic exercise affected the cognition of patients with mild vascular cognitive impairment (VCI) - cognitive decline caused by mini-strokes regarded as being the second leading cause of dementia behind Alzheimer's disease.
Participants were randomly assigned to either a group that did supervised aerobic exercise or a group that received the usual form of care and attended a monthly nutrition seminar. The participants were then followed for 6 months, with 62 participants completing the full study.
The researchers found that the participants in the exercise group experienced significant improvements in their cognitive function compared with the group receiving the usual form of care. Brain scans carried out both before and after the study also demonstrated that the brains of the exercising group became more efficient with training.
"While these promising results need to be replicated in larger and more diverse populations, the fact that aerobic exercise can improve cognitive function in VCI means that people with the condition have hope there may soon be a proven tool they can use to prolong their independence and improve their quality of life," concludes study author Teresa Liu-Ambrose.
Studies 'highlight value of non-drug therapies'
Not only do these studies suggest a potentially effective form of treatment for Alzheimer's disease and associated conditions, but they suggest one that it is relatively easy to deliver to a wide population of patients.
"These findings also highlight the potential value of non-drug therapies for Alzheimer's disease and other dementias, and remind us that research ought to adamantly pursue combination and multi-modal approaches to Alzheimer's therapy and prevention," concludes Carrillo.
For more from the 2015 Alzheimer's Association International Conference, our Spotlight feature this week covers some of the highlights.