DURHAM, N.C. – The team of Duke University Medical Center researchers who demonstrated in late 1999 that aerobic exercise is just as effective as medication in treating major depression in the middle-aged and elderly has now reported that the same exercise program also appears to improve the cognitive abilities of these patients.
The researchers found significant improvements in the higher mental processes of memory and the so-called executive functions, which include planning, organization and the ability to mentally juggle different intellectual tasks at the same time. These improvements were above and beyond what would be expected after the depression had lifted, the researchers said.
"What we found so fascinating was that exercise had its beneficial effect in specific areas of cognitive function that are rooted in the frontal and pre-frontal regions of the brain," said James Blumenthal, Duke psychologist and study principal investigator.
Other cognitive functions that were measured by the team -- attention, concentration and psychomotor skills -- did not appear to be affected by the exercise program. Interestingly, the researchers noted, different regions of the brain are responsible for these abilities.
The results of the Duke study, funded by a grant from the National Institute of Mental Health (NIMH), were published in the January issue of the Journal of Aging and Physical Activity.
"The implications are that exercise might be able to offset some of the mental declines that we often associate with the aging process," Blumenthal said. "Further studies are warranted not only to clarify specific mental processes that are improved by exercise, but to better understand the underlying mechanisms of these improvements."
While it is unclear why exercise would improve mental functioning of these patients, Blumenthal believes that it could be influenced by the improved flow of oxygen-rich blood to specific regions of the brain.
"We know that in general, exercise improves the heart's ability to pump blood more effectively, as well as increases the blood's oxygen-carrying capacity," Blumenthal said. "It is thought that one of the reasons why the elderly – especially those with coronary artery disease or hypertension – tend to suffer some degree of cognitive decline is in part due to a reduction in blood flow to the brain.
"So it may be that just as exercise improves muscle tone and function, it may have similar effects on the brain," he said. In the original exercise and depression study, dubbed SMILE (Standard Medical Intervention and Long-term Exercise), the researchers followed 156 patients between the ages of 50 and 77 who had been diagnosed with major depressive disorder (MDD). They were randomly assigned to one of three groups: exercise, medication, or a combination of medication and exercise.
The exercise group spent 30 minutes either riding a stationary bicycle or walking or jogging three times a week. The anti-depressant used by the medication group was sertraline (trade name Zoloft), which is a member of a class of commonly used anti-depressants known as selective serotonin reuptake inhibitors.
To the surprise of the researchers, after 16 weeks, all three groups showed statistically significant and identical improvement in standard measurements of depression, implying that exercise was just as effective as medication in treating major depression. Not only did study participants take a standard battery of tests for depression, they took a series of standardized tests aimed at measuring the cognitive abilities of four separate domains: memory, executive functioning, attention/concentration and psychomotor speed. These tests were taken before enrolling in the trial and four months later.
After comparing the test results from the 42 members of the exercise group to the 42 members of the medication group, the researchers found that exercise seemed to have a beneficial effect on selective areas of cognitive functioning, and that the level of depression also seemed to play a role.
"The participants with milder depression at the beginning of the trial were more likely to show an improvement in the executive functioning domain, while those with moderate to severe depression showed less improvement," Blumenthal said. To better understand this phenomenon, Blumenthal and his colleagues are now enrolling participants in another NIMH-funded study, called SMILE-II. Participants must be clinically depressed, over the age of 50, and must be physically able to exercise.
The research team included, from Duke, Parinda Khatri, Michael Babyak, Steve Herman, Teri Baldewicz, David J. Madden, Dr. Murali Doraiswamy, Dr. Robert Waugh, and Dr. Ranga Krishnan. Edward Craighead, University of Colorado at Boulder, was also a member of the team.
Materials provided by Duke University Medical Center. Note: Content may be edited for style and length.
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