Published on: December 21, 2017
by Kate Kneisel for MedPage Today:
A daily serving of green leafy vegetables may help slow age-related decline in memory and thinking, researchers reported.
The prospective study of 960 people (average age 81) from the Memory and Aging Project (MAP) assessed participants’ self-reported eating habits on the Food Frequency Questionnaire (FFQ), and tested their thinking and memory skills annually over an average of almost 5 years, according to Martha Clare Morris, ScD, of Rush University Medical Center in Chicago, and colleagues.
Compared with the one-fifth of participants who consumed the least amount of leafy green vegetables (0.1 average servings/day), the one-fifth who consumed the most (1.3 average servings/day) slowed their cognitive decline by an average of 0.05 standardized units per year (P=0.0001) after adjustments, they wrote in Neurology.
The difference between the two groups was the equivalent of a delay of 11 years in cognitive aging, Morris told MedPage Today.
However, the results do not show causation, the authors warned. “This study is part of an evolving field that is identifying foods and nutrients that protect the brain with age,” Morris said.
Citing their own and supporting data of two prior prospective studies, the researchers concluded that “consumption of green leafy vegetables [1-2 servings per day] and foods rich in phylloquinone (vitamin K), lutein, nitrate, folate, alpha-tocopherol, and kaempferol may help to slow decline in cognitive abilities with older age.”
The study population was 74% female, with about 15 years of education. The majority (95%) were white and 98.5% were non-Hispanic. They came from MAP, an open cohort study that has been enrolling retired individuals who are free of dementia in the Chicago area since 1997. Because the study focused on older adults and the majority of participants were white, the results may not apply to younger adults and minorities, Morris noted.
Respondents were divided into five equal groups from lowest to highest intake of green leafy vegetables. The three green leafy vegetable items and their serving sizes on the FFQ included spinach (½ cup cooked), kale/collards/greens (½ cup cooked), and lettuce salad (1 cup raw).
The study did not assess supplement intake, given the focus on food-sources of nutrients, and the overall lack of research suggesting a protective benefit of vitamin supplements on cognitive decline, Morris’ group noted.
Compared with those participants consuming the least green leafy vegetables, those with the highest intake were more likely to be higher educated, male, to participate more frequently in cognitive and physical activities, and to have fewer cardiovascular conditions and depressive symptoms.
Noting that the nutrients provided by green leafy vegetables may have independent mechanisms of action that synergistically protect the brain, Morris’ group also assessed the link between the individual nutrients and rate of cognitive decline, after adjusting for the effects of age, sex, education, smoking history, physical activity, participation in cognitive activities, alcohol consumption, total energy intake (green leafy model only), and seafood consumption.
With the exception of beta-carotene, the association remained significant for each of the nutrients and bioactives. Compared with the group with the lowest intake of green leafy vegetables, those with the highest intake had the following reductions in rate of cognitive decline (β, standardized units):
Secondary analyses found that results remained significant after adjustments for cardiovascular conditions, depressive symptoms, low weight (BMI≤20), obesity (BMI≥30), with a difference between the groups with highest and lowest leafy greens intake of 0.04 standardized units (P<0.001). Results also remained significant in separate analysis that included 220 participants identified as having mild cognitive impairment.
David Knopman, MD, of the Mayo Clinic in Rochester, Minnesota, told MedPage Today that the study was well done, with data from a “well-regarded, longitudinal, epidemiological study. Aside from potential confounding by unmeasured or unmeasurable factors, the biggest conceptual weakness in observational studies of diet is whether a dietary pattern at one point in time is at all reflective of patterns earlier in life. If that is the case, then it is a bit misleading to propose switching from a veggie-free diet to a high leafy vegetable diet in one’s 8th decade of life; [that] may have limited value.”
The take-home message is that “leafy green vegetables are good for cognitive health, but when in one’s life course that becomes relevant is unknown,” concluded Knopman, who was not involved in the study, and disclosed his status as “an avowed meat and potatoes guy.”
Morris told MedPage Today that “studies find that eating patterns in middle-age and later years are pretty stable,” adding that it is never too early or too late to get the benefits of eating leafy green vegetables.
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