From Medscape Medical News
Pam Harrison
January 21, 2010 — A high-intensity, supervised aerobic exercise program improves cognitive performance in older adults with mild cognitive impairment (MCI), a new study suggests. The effects are most pronounced in women despite comparable gains in cardiorespiratory fitness and body fat reduction in both sexes.
The results, published in the January issue of the Archives of Neurology, showed that a 6-month aerobic exercise program improved performance on multiple tests of executive function in women with MCI. The same exercise regimen also improved insulin sensitivity and reduced stress hormones in women but had much less effect in men.
"What we know is that generally with age or disease, we use glucose less efficiently and then we see cognitive problems," Laura Baker, PhD, University of Washington School of Medicine, Seattle, told Medscape Neurology. "So if we can increase the efficacy of glucose metabolism, we may be improving the efficacy with which glucose gets to the brain and therefore improve cognition. This happened for women but not for men."
Aerobics vs Stretching
For the study, 33 adults, of whom 17 were women, with amnestic MCI were randomized to either a high-intensity aerobic exercise program or a stretching control group. "The aerobic group exercised under the supervision of a fitness trainer at 75% to 85% of heart rate reserve for 45 to 60 minutes per day, 4 days per week for 6 months," the investigators note.
The control group followed the same schedule during which they performed supervised stretching activities but maintained their heart rate at or below 50% of their heart rate reserve. Glucometabolic and treadmill tests were done before and after the study on all participants, and blood was collected and the cognitive test administered at baseline and again at months 3 and 6.
The first 8 sessions were supervised by the trainer, and thereafter, the trainer supervised 1 session per week per participant. "Six months of controlled aerobic exercise vs stretching improved cardiorespiratory fitness indexed by exercise treadmill test measures of VO2 peak ... treadmill grade ... and treadmill time to exhaustion," the investigators report.
The same aerobic regimen also improved executive control processes of multitasking, cognitive flexibility, information processing efficiency, and selective attention. When sex was included in the model as a predictor variable, they write, "a significant interaction indicated that this treatment effect differed for men and women, [whereas] for women, increasing VO2 peak was associated with improved executive function."
Favorable effects of aerobic exercise were also apparent for Symbol-Digit Modalities and Verbal Fluency, measures of cognitive function, with analyses again revealing that the effect size was larger for women than for men on both tasks. Sex differences were also observed on the Stroop test, with aerobic exercise having no effect in men. The aerobic group was also faster to complete the Trails B test compared with baseline than the stretching control group; here, the effect was similar for women and men.
"Aerobic exercise was [also] associated with sex-specific improvements in glucoregulation and insulin sensitivity," the study authors note, "and for women, 6-month changes in insulin sensitivity predicted VO2 peak and executive function."
A sex-specific effect of aerobic exercise was again observed for plasma cortisol levels, increasing for women in the stretching control group over the study interval but not for women in the aerobic group. In men, cortisol levels decreased over time for those in the stretching group, whereas they remained stable for the aerobic group.
Aerobic exercise also reduced brain-derived neurotrophic factor (BDNF) in women but not in men.
Initiate and Organize
As Dr. Baker observes, the first cognitive ability to be affected in patients with MCI is their ability to initiate and to organize. "Generally, it's the little things like cleaning up or finishing off projects, and exercise is no different than any other task." Patients with MCI are also afraid to exercise, and they have no confidence that if they exercise they might do it right.
Thus, these people need help to "get the ball rolling," she adds. Once a structure is in place, however, and they get started on an exercise regimen, "they are really fine." Indeed, after the first 6 weeks of their exercise regimen during which patients were worked up to their target heart rate very slowly, "we were exercising them at a pretty high level, and by week 6, many of them were going over their target [heart rate]," Dr. Baker notes.
"Evidence already shows that there is a benefit from exercise for normal older adults with no specific memory problems, and our hope is that prolonged exercise may slow progression in cognitive decline in patients with MCI because even if we can't reverse cognitive decline altogether, if we can give someone a better quality of life for many months, that would be a huge accomplishment," Dr. Baker observes.
In a related but separate study published in the same issue of Archives of Neurology by Yonas Geda, MD, and colleagues at the Mayo Clinic in Rochester, Minnesota, moderate exercise done during mid or even later in life reduced the risk of MCI by 39% in adults with normal cognitive function at baseline.
Findings in this study were consistent among both men and women.
Important Gap
Art Kramer, PhD, University of Illinois at Urbana-Champaign, told Medscape Neurology that the study begins to fill an important gap toward a better understanding of the potential impact exercise may have in MCI patients. "There are many exercise studies with relatively healthy older individuals but very few with MCI or Alzheimer's disease, and rigorously controlled trials are important."
In their own meta-analysis of fitness and cognition (Psychol Sci. 2003;14:125-130), Dr. Kramer and colleagues also found that fitness positively affects cognition.
"Consistent across the many studies, the effect of exercise was larger for women than it is for men," he adds. On the other hand, the current study, although well controlled, still involves only a small sample and perhaps the lack of effect from aerobic exercise in men may be explained by the limited numbers of patients in the study overall.
"As the authors themselves suggest, this is preliminary data and it needs to be replicated ideally in a larger randomized controlled trial of MCI patients and perhaps even those further along with Alzheimer's disease," Dr. Kramer observes. Still, he adds, "the study attempts to relate the effects of exercise on cortisol and BDNF to animal work in which we have more physiological and neurological measures, which is a good step."
The study was supported by the Department of Veterans Affairs and the Alzheimer’s Association. The authors have disclosed no relevant financial relationships. Dr. Kramer has disclosed no relevant financial relationships.
Arch Neurol. 2010;67:71-79, 80-86.
No comments:
Post a Comment