The DASH diet, combined with aerobic exercise and reduced calories, was associated with improved EFML and psychomotor speed performance relative to controls. The beneficial effects in the DASH+WM group were particularly pronounced for individuals with higher levels of IMT at baseline, a group at increased risk of stroke. Individuals who ate the DASH diet without losing weight or exercising exhibited improved psychomotor speed performance relative to controls, although EFML was not improved. We also observed that improvements in EFML in the DASH+WM group were mediated by improved cardiorespiratory fitness, whereas improvements in psychomotor speed were mediated by weight loss. It is unclear what mediated the effects of the improvements in psychomotor speed among the DASH-A group.
Several recent observational studies have reported that diet and exercise are related to improved neurocognition. Scarmeas et al21
demonstrated that physical activity and high adherence to the Mediterranean diet (similar in nutrient content to the DASH diet) were associated with reduced risk of AD and that exercise and diet had an additive effect. In addition, Feart et al22
demonstrated that better adherence to the Mediterranean diet was associated with slower cognitive decline on the Mini-Mental Status Examination but did not reduce the incidence of AD.
Aerobic exercise interventions generally have been found to result in modest neurocognitive improvements in attention and executive function, although the majority of individual trials have yielded null or equivocal findings.19
Interventional studies of dietary supplements and neurocognition, including antioxidants (vitamins C and E); vitamins B6, B12, and folate; fatty acids33
; and caloric restriction34
also have provided negative or equivocal results. To our knowledge, the present study is the first randomized trial to examine the combined effects of diet and exercise on neurocognition in adults at risk for neurocognitive decline because of HBP.
We also explored potential treatment moderators and possible mechanisms of improvement in neurocognition. Our finding that improved aerobic fitness mediated improvements in EFML supports findings from several smaller interventions using neuroimaging, which have shown that improved peak oxygen volume increases anterior white matter integrity and gray matter volume.29
Our findings that both SBP and IMT moderated the effects of diet and exercise on neurocognition suggest that individuals with vascular disease may be especially likely to benefit from aerobic exercise and diet.
Because our trial consisted of a 4-month intervention, the extent that these improvements could be maintained over time is not known. Second, the clinical significance of these improvements is not known, and a larger cohort followed over a longer time interval would be required to determine whether the intervention affected rates of AD. Third, the mechanisms for these improvements are not known, and it is possible that the observed improvements in neurocognitive function could be mediated by other factors, such as inflammation, growth factors, or other neurochemical changes not measured in the present study. Fourth, other diets, such as the Mediterranean diet alone or combined with exercise or weight loss, also could be beneficial. Fifth, because the current trial design did not use an exercise control group without dietary modification or a weight loss control group, it is unclear to what extent exercise or caloric restriction contributed to the observed pattern of findings. Although the DASH+WM and DASH-A groups were not statistically different when compared directly, our study was not powered to detect treatment group differences in neurocognitive performance specifically. Finally, although our sample included individuals with HBP who were not on medication, it is unclear whether our findings generalize to individuals with higher BP or more severe cardiovascular disease. Future studies should, therefore, examine the effects of aerobic exercise, dietary modification, and caloric restriction in other populations.
The results of this study indicated that the DASH diet, especially when associated with caloric restriction and aerobic exercise, improve neurocognitive performance among individuals with HBP. Improvements in neurocognitive performance were most pronounced among individuals with poorer vascular health. Dietary modification according to the DASH diet also appears to improve psychomotor functions. These improvements appear to be mediated by improved cardiorespiratory fitness and reduced body weight. The present findings could have important implications for improving neurocognitive function among older adults with HBP, at greater risk for cognitive decline and AD. Future studies should, therefore, examine the effects of diet and exercise in adults at elevated risk for dementia.