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Expert Opinion: Green leafy vegetables protective against cognitive decline?

Green leafy vegetables protective against cognitive decline?

Background

As life expectancy rises worldwide, so does the prevalence of dementia. Consequently, there is a great need for knowledge regarding preventive measures. Nutritional intake is likely to influence cognitive health, but the specific role of different food items remains unclear. Two large prospective studies previously investigated the relation between several types of vegetables and cognitive decline.¹·² Both studies showed an association between green leafy vegetables (spinach, kale, collards and lettuce) and a slower rate of cognitive decline. The research discussed in this article aimed to identify the individual nutrients that may contribute to the underlying protective mechanisms of green leafy vegetables.

Summary of abstract 

Morris, M. C., Wang, Y., Barnes, L. L., Bennett, D. A., Dawson-Hughes, B., & Booth, S. L. (2018). Nutrients and bioactives in green leafy vegetables and cognitive decline: Prospective study. Neurology, 90(3), e214-e222.

 Objective

To increase understanding of the biological mechanisms underlying the association, the individual relations to cognitive decline of the primary nutrients and bioactives in green leafy vegetables, including vitamin K (phylloquinone), lutein, β-carotene, nitrate, folate, kaempferol, and α-tocopherol was investigated.

Methods

This was a prospective study of 960 participants of the Memory and Aging Project, ages 58–99 years, who completed a food frequency questionnaire and had ≥2 cognitive assessments over a mean 4.7 years.

Results

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 (median 1.3 servings/d) was slower by β = 0.05 standardized units (p = 0.0001) or the equivalent of being 11 years younger in age. Higher intakes of each of the nutrients and bioactives except β-carotene were individually associated with slower cognitive decline. In the adjusted models, the rates for the highest vs. the lowest quintiles of intake were β = 0.02, p = 0.002 for phylloquinone; β = 0.04, p = 0.002 for lutein; β = 0.05, p < 0.001 for folate; β = 0.03, p = 0.02 for α-tocopherol; β = 0.04, p = 0.002 for nitrate; β = 0.04, p = 0.003 for kaempferol; and β = 0.02, p = 0.08 for β-carotene.

Conclusions

Consumption of approximately 1 serving per day of green leafy vegetables and foods rich in phylloquinone, lutein, nitrate, folate, α-tocopherol, and kaempferol may help to slow cognitive decline with aging.

Review

This is an elegant prospective cohort study investigating the relation between green leafy vegetable intake and cognitive decline. Strengths of this research include the large cohort and the annual follow-up visits (mean follow-up 4.7 years) to measure change in cognitive abilities over time by in-person administration. There are also some limitations in this study. The sample consists of well-educated participants in an open cohort study requiring organ donation after death for participation.
In addition, 95% of the participants are Caucasian and all originate from the Chicago area. The results of this study might therefore not be applicable for persons from different origin or race. Further, supplement intake was not considered in this study as this study concentrated on food-derived intake. However, confounding by supplement intake is possible and might be interesting to take into account.

Conclusion

This interesting work by Morris et al. is a step forward in unraveling the relation between nutritional intake and cognitive function in the aging population. Various promising nutrients rich in green leafy vegetables were highlighted and are of interest for further research. It would be of great interest to include blood levels of these nutrients in future studies to further elucidate the role of individual nutrients on cognitive decline.

F. de Leeuw & K. Engelfriet

References

  1. Kang, Jae H., Alberto Ascherio, and Francine Grodstein. “Fruit and vegetable consumption and cognitive decline in aging women.” Annals of neurology 57.5 (2005): 713-720.
  2. Morris, M. C., et al. “Associations of vegetable and fruit consumption with age-related cognitive change.” Neurology 67.8 (2006): 1370-1376.

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