Green Leafy Vegetables Linked to Slower Cognitive Decline

January 08, 2018

Eating one serving of green leafy vegetables per day may help to slow cognitive decline with aging, a new study suggests.

In the prospective study of an older US community population, consumption of green leafy vegetables was linearly associated with slower cognitive decline.

The rate of decline among those who consumed one to two servings per day was the equivalent of being 11 years younger compared with those who rarely or never consumed green leafy vegetables, the researchers say.

Investigation of the nutrients for which green leafy vegetables are a rich or primary source indicated that higher food intakes of folate, phylloquinone, and lutein were each linearly associated with slower cognitive decline and appeared to account for the protective correlation of green leafy vegetables to cognitive change.

"This adds to previous evidence that leafy greens may slow cognitive decline, but we have taken it a step further by investigating which nutrients in these vegetables may be responsible for the protective association," lead author, Martha Clare Morris, ScD, Rush University, Chicago, Illinois, commented to Medscape Medical News. "And we have identified a few that seem to be important — some of which were not known to associated with brain heath before."

"Our main take-home message is that leafy greens contain so many good nutrients, several which are linked to better cognitive function," she added, "so this is a food that should definitely be a staple in everyone's diet, particularly older individuals." 

The study was published online in Neurology on December 20.

Other experts in the field were enthusiastic about the findings. 

"This study adds to the rapidly evolving and convincing evidence that you are what you eat when it comes to brain health," Richard Isaacson, Weill Cornell Medicine, New York City, said. "From a practical clinical perspective, regular intake of green leafy vegetables should be a standard part of a risk reduction paradigm to delay cognitive decline throughout the lifespan."

Yian Gu, MD, Columbia University and the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, New York City, added: "This is a very interesting study which adds to the existing literature of a beneficial role of vegetables on slowing cognitive decline. Overall, I think the results from longitudinal studies like this one can be very encouraging in terms of improving our dietary strategy to prevent cognitive decline or even dementia in older adults."

"It might still be too early, though, to recommend increasing intake of green leafy vegetables, without further confirmation in the intervention studies," Dr Gu cautioned. "In addition, one may also need to take into consideration other food intake. Increasing vegetable intake but also increasing 'bad foods' intake at the same time might not be as helpful."

Joseph Quinn, MD, Oregon Health and Science University, Portland, called the paper "good work from an excellent group of investigators." 

"Your mother was right," Dr Quinn said. "Eat your vegetables, especially the green leafy ones."

The current study involved 960 individuals taking part in the Rush Memory and Aging Project, which includes volunteers from more than 40 retirement communities, senior public housing units, and churches and senior centers in the Chicago area.  Participants were free of dementia at enrollment and underwent annual clinical evaluations and food-frequency questionnaires. 

The average age of participants was 81 years, 74% were female, and they had a mean educational level of 14.9 years. The mean follow-up was 4.7 years.

Green leafy vegetable intake ranged from a mean 0.09 servings per day for those in the lowest quintile of intake to a mean 1.3 servings per day for the highest quintile.

On average, the sample declined in global cognitive scores over time at a rate of 0.08 standardized units/year.

In a linear mixed model adjusted for age, sex, education, participation in cognitive activities, physical activities, smoking, and seafood and alcohol consumption, consumption of green leafy vegetables was associated with slower cognitive decline. The decline rate for those in the highest quintile of intake was slower by β = 0.05 standardized units (P = .0001) compared with lowest quintile — the equivalent of being 11 years younger in age.

There was no evidence that the association was mediated by cardiovascular conditions, and in further analyses adjusted for depressive symptoms, low weight (body mass index [BMI]  ≤ 20), and obesity (BMI ≥  30), conditions that may be both causes and effects of dementia processes, the estimate of effect remained unchanged and statistically significant (β for Q5 vs Q1 = 0.04; P < .001).

The researchers also found that food sources of folate, phylloquinone, lutein, nitrate, α-tocopherol, and kaempferol were each positively and significantly associated with slower rates of cognitive decline. A weaker association was observed with dietary intake of β-carotene.

Another analysis showed that the protective effect of green leafy vegetables on cognitive decline was reduced and no longer statistically significant after adjustment for intake of phylloquinone, lutein, or folate, suggesting that these nutrients were the source of the effect on cognitive decline.

To investigate the possibility of the results being due to inaccurate reporting of dietary intake by those who had cognitive impairment at baseline, the researchers eliminated 220 individuals who had mild cognitive impairment at baseline. But the effect estimates changed minimally and remained statistically significant.

The results also remained the same after exclusion of 144 participants whose green leafy vegetable consumption increased or decreased over the study.

The authors note that their findings are supported by two previous large prospective studies that examined the relations of different types of vegetables on cognitive decline. In both studies, the consumption of green leafy vegetables, including spinach, kale, collards, and lettuce, had the strongest association with slowed cognitive decline.

They say that the nutrients suggested to be protective in this study may have independent mechanisms of action that synergistically protect the brain. They point out that serum carotenoid levels have been associated with less severe periventricular white matter lesions, particularly in older smokers; lutein has been shown to reduce phospholipid peroxidation in human erythrocytes and to attenuate oxidative stress and mitochondrial dysfunction and neuroinflammation. In addition, folate inhibits tau phosphorylation and other pathologies of Alzheimer's disease.

The study was supported by grants R01 AG031553 and R01 AG17917 and the US Department of Agriculture Agricultural Research Service cooperative agreement 58-1950-7-707.  The researchers have disclosed no relevant financial relationships. 

Neurology. Published online December 20, 2017. Abstract

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