Six months of regular aerobic exercise led to improved executive functioning in adults at risk for cognitive decline, researchers for the ENLIGHTEN trial reported.
In a randomized clinical trial of exercise and diet in sedentary adults with cognitive impairment but no dementia (CIND) and cardiovascular risk factors, regular aerobic exercise three times a week for 6 months was tied to significant improvements in executive function, but not in memory or language/verbal fluency domains, according to James Blumenthal, PhD, of Duke University Medical Center in Durham, N.C., and colleagues.
And while the DASH (Dietary Approaches to Stop Hypertension) diet boosted the executive functioning benefits of exercise, it did not show any cognitive function benefit by itself, they wrote in Neurology.
“An interesting finding is that the DASH diet alone did not provide any benefit for cognitive function, even though the DASH diet did improve cardiovascular health,” observed Teresa Liu-Ambrose, PhD, PT, of the University of British Columbia in Vancouver, who was not involved with the study. “However, it should be noted that aerobic exercise not only improves cardiovascular health, but also induces the release of growth factors that are beneficial for neuronal health.”
While participants who engaged in both aerobic exercise and DASH demonstrated the most improvement in executive functions, the difference in the magnitude of benefit — of exercise alone versus exercise plus DASH — was 25%, Liu-Ambrose told MedPage Today. “As adoption and adherence to health habits is often a challenge for individuals, one may consider adopting one habit first, i.e., exercise, and then slowly incorporating the second habit, i.e., diet,” she said.
The ENLIGHTEN trial used a 2-by-2 factorial design (exercise/no exercise and DASH/no DASH) to compare the independent effects of exercise and diet on an array of cognitive abilities. At baseline, participants had subjective memory complaints, objective evidence of cognitive impairment, and at least one additional cardiovascular disease risk factor besides being sedentary. They had a mean age of 65.4 and 66% were female.
Researchers randomly assigned 160 inactive men and women to 6 months of either exercise alone (n=41), DASH diet alone (n=41), combined exercise and DASH diet (n=40), or a no-exercise, no-diet control group that received weekly phone calls about health-related topics (n=38). Effect sizes were measured with the Cohen d to indicate the difference between means.
Participants in the exercise group worked out under supervision three times a week for 35 minutes at 70% to 85% of their initial peak heart rate reserve for 3 months, then continued exercising at that rate at home, documenting activity in weekly exercise logs. DASH diet group members received education about the DASH diet and frequent feedback about adherence from a nutritionist.
At the end of 6 months, participants who engaged in aerobic exercise (beta coefficient 4.2, 95% CI 0.2-8.2, d=0.32, P=0.046), but not those only in the DASH group (beta coefficient 3.7, 95% CI −0.2 to 7.7, d=0.30, P=0.059), demonstrated significant improvements in the executive function domain. There were no significant improvements in the memory or language/verbal fluency domains.
The largest improvements in executive functioning occurred for participants in the combined exercise and DASH diet group (d=0.40, P=0.012) compared with controls. To illustrate the potential clinical significance of this, the authors estimated that participants had average scores for select subtests of executive function consistent with 93-year-old people at baseline — 28 years older than their chronological age. After 6 months, people who exercised and followed the DASH diet had average executive function scores corresponding to 84-year-olds, a 9-year improvement. In contrast, executive function scores for control group participants worsened by a half year (which actually was the duration of the study).
“Individuals with CIND — cognitive impairment, no dementia — are at risk for developing dementia over time,” Blumenthal said. “Currently there are no known treatments to prevent the progression of this disorder, so findings from this study are very important by suggesting that regular exercise can improve cognitive function and potentially delay the onset of dementia in these individuals.”
“These findings raise the possibility that adopting a healthy lifestyle of diet and exercise can not only reduce the risk of heart disease, but also reduce the risk of developing dementia later in life,” he added. “Future studies, with larger samples followed over more extended time periods are needed, along with studies that examine the mechanisms by which these lifestyle modifications improve cognitive functioning,” he told MedPage Today.
The ENLIGHTEN trial may have been underpowered to detect differences between aerobic exercise and DASH diet alone, Blumenthal and co-authors noted; because of this potential limitation, they provided limited evidence of the relative benefits of these two interventions. The study also was only 6 months long and longer-term effects of exercise and diet on cognitive outcomes are unknown. No one dropped out of the study and trial results may not apply to less motivated groups, they added.
The study was supported by the National Heart, Lung, and Blood Institute.
Blumenthal and co-authors disclosed no relevant relationships with industry.