March 11, 2010 — The low-sodium, low-fat Dietary Approaches to Stop Hypertension (DASH) diet, combined with aerobic exercise and caloric restriction, improves neurocognitive function among sedentary, overweight, or obese patients with high blood pressure, a new study has found.
The study also shows that the beneficial effects of this combined approach are particularly pronounced in subjects with higher carotid artery intima-media thickness (IMT) who are at higher risk for a stroke.
"The present findings could have important implications for improving neurocognitive function among older adults with HBP [high blood pressure], at greater risk for cognitive decline and Alzheimer's disease," write Patrick J. Smith, from the Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina, and colleagues. "Future studies should therefore examine the effects of diet and exercise in adults at elevated risk for dementia."
As part of the larger ENCORE (Exercise and Nutrition intervention for CardiOvasculaR hEalth) study, 124 participants with elevated blood pressure (systolic 130 - 159 mm Hg or diastolic 85 - 99 mm Hg) who were sedentary and had a body bass index of 25 to 40 kg/m2 were randomly assigned to the DASH diet alone, the DASH diet combined with a behavioral weight management program, or to a usual diet control group. The patients were not taking antihypertensive medications.
Patients in the DASH-alone group received instructions about modifying their diet but did not exercise or lose weight. The DASH plus weight management group received the same DASH dietary advice and participated in a weight management program that consisted of a 30-minute supervised aerobic exercise program 3 times a week and weekly group counseling sessions focused on behavioral weight loss strategies. Patients in the diet control group maintained their usual dietary habits, did not lose weight, and did not exercise during the 4-month study.
At baseline, researchers used high-resolution ultrasound studies to measure the IMT of the left and right common carotid arteries. At baseline and after 4 months, participants completed a battery of neurocognitive tests to assess performance in the domains of Executive Function-Memory-Learning (EFML) and Psychomotor Speed.
Adherence rates were excellent: participants in the DASH plus weight management group and DASH-alone group attended 92% of the information classes, and those in the DASH plus weight management group attended 90% of the exercise sessions.
Significant Improvements Noted
The DASH plus weight management group had improved EFML relative to the control group (effect size [ES], 0.21; 95% confidence interval [CI], 0.03 - 0.39; Cohen's d = 0.562; P = .008), although the DASH-alone group did not improve relative to the control group.
The improvements in the DASH plus weight management group were comparable to a 14.6-year improvement in predicted age for Trail Making Test B-A performance (speed of drawing consecutive lines between numbers and between numbers and letters), and a 6.1-year improvement for Stroop Interference performance (speed of identifying and differentiating colors and words from lists). In contrast, the control group's performance was comparable to a 9.4-year poorer performance for Trail Making Test B-A and an 11.7-year poorer Stroop Interference performance.
Similar results were observed for the Psychomotor Speed with the DASH plus weight management group (ES, 0.18; 95% CI, 0.02 - 0.33; Cohen's d = 0.480; P = .023) and DASH alone group (ES, 0.15; 95% CI, 0.00 - 0.30; Cohen's d = 0.440; P = .036) exhibiting significant improvements relative to the control group.
The researchers found that the participants with greater IMT, and therefore in poorer vascular health, and higher systolic blood pressure showed greater improvements in EFML in the DASH plus weight management group.
"Our finding that both SBP [systolic blood pressure] and IMT moderated the effects of diet and exercise on neurocognition suggests that individuals with vascular disease may be especially likely to benefit from aerobic exercise and diet," the study authors write.
Improvements in EFML in the DASH plus weight management group were mediated by improved cardiorespiratory fitness, whereas improvements in Psychomotor Speed were mediated by weight loss.
Subjects in both treatment groups had lower blood pressure vs the control group, with the DASH plus weight management group having the greatest reduction. The DASH plus weight management group lost the most weight and had the best aerobic capacity.
Possible Protection Against Alzheimer's Disease?
It is not known whether the benefits uncovered by this study can be maintained with time or whether the intervention could affect rates of Alzheimer's disease, said the study authors. Although the study does not reveal the mechanisms for improved cognitive function, "it's possible that the observed improvements in neurocognitive function could be mediated by other factors such as inflammation, growth factors, or other neurochemical changes," they write.
Other healthy diets such as the Mediterranean diet may also be beneficial, they said.
According to background information in the study, an estimated 1 billion men and women worldwide have prehypertension or hypertension. High blood pressure affects 50% of adults 60 years and older and has a lifetime prevalence of 90%. High blood pressure is associated with an increased risk for Alzheimer's disease, mild cognitive impairment, and vascular dementia.
Other studies have shown that lifestyle changes, including diet and exercise, reduce blood pressure and weight, improve neurocognitive function, and may protect against incident Alzheimer's disease, but this study is believed to be the first randomized clinical trial to examine the combined effects of dietary modification and aerobic exercise on neurocognitive function among overweight individuals with high blood pressure.
The study authors have disclosed no relevant financial relationships.
Circulation. Published online March 8, 2010.
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