Exercise and Your Brain: Should You Sweat It?
Sorting out the confusing research on physical activity and cognition.
While observational studies have shown an association between physical activity and lower rates of mental decline, findings from randomized clinical trials have been mixed. And now the largest and longest such trial has reported surprisingly disappointing results: The Lifestyle Interventions and Independence for Elders (LIFE) study, a 24-month trial involving 1,635 sedentary adults ages 70-89, found no difference in cognitive scores among those assigned to a physical activity program and a control group. Nor was there any meaningful difference in incidence of Alzheimer’s and dementia.
But don't trade your running shoes for the TV remote just yet. "It’s not unusual for results of randomized clinical trials to be inconsistent with observational studies," cautions Tammy Scott, PhD, a scientist at Tufts' HNRCA Neuroscience and Aging Laboratory. She notes that the control group was assigned to regular interactive seminars for health education, which may have had its own brain benefits: "The education intervention was both cognitively and socially stimulating, both of which have been shown to be beneficial in maintaining cognitive health."
Indeed, as the LIFE researchers acknowledged, neither the physical-activity group nor the control group showed declines in cognitive scores over the 24 months.
TOUGH ENOUGH?: Roughly half the participants, who were sedentary and at risk for mobility disability, were assigned to the moderate-intensity exercise program. The goal was to progress toward a goal of 30 minutes of walking, 10 minutes of strength training and 10 minutes of balance and flexibility activity, five to six times weekly.
"We don’t actually know if cardiorespiratory function improved," comments Roger A. Fielding, PhD, director of Tufts' HNRCA Nutrition, Exercise, Physiology and Sarcopenia Laboratory, "although I would expect that an intervention of this type would improve cardiorespiratory fitness in this group of individuals. It may be that the improvement was not sufficient to induce changes in cognitive function."
OLDER AND WEAKER: Physical activity may also have brain benefits for specific groups. The LIFE researchers, led by Kaycee M. Sink, MD, of Wake Forest University, reported that participants ages 80 and older and those with lower initial physical functioning levels did see improved "executive function" from the exercise program. Executive function - the ability to plan, organize and prioritize - is crucial to independent daily living, they noted.
In an accompanying editorial in JAMA, Sudeep Gill, MD, and Dallas Seitz, MD, PhD, of Queen’s University in Canada, wrote, “The effects of exercise on cognition also may differ in adults without cognitive concerns (as was the case in the LIFE trial) when compared with individuals with cognitive concerns, mild cognitive impairment or dementia.… Optimizing physical activity should be encouraged at every age—not just when symptoms of cognitive decline appear.”
BRAIN SCANS: Other recent findings, in fact, continue to support a role for physical activity in protecting the brain. In results reported at the Alzheimer’s Association International Conference - and so not yet published in a peer-reviewed journal - previously sedentary older adults who started exercising showed brain improvements in MRI scans. The 71 participants were split between a control group and one assigned to exercise; all wore heart-rate monitors to ensure different activity levels between the groups.
Scans of the exercise group showed improved blood flow in brain regions important to thought processing and memory, and exercisers also improved in tests of executive function. Most intriguing were spinal-fluid tests that in the exercise group indicated a reduction in the telltale "tau" proteins associated with Alzheimer's disease. The researchers are now launching a similar 18-month national study that will test exercise benefits in people with mild cognitive impairment, often a precursor to Alzheimer's.