People who ate one serving of green, leafy vegetables performed better on learning/memory tests and showed an equivalent of being 11 years younger cognitively than people who rarely ate them. This was an observational study so causation cannot be established. However, this study accounted for other factors that may affect brain health including seafood and alcohol consumption, smoking, high blood pressure, obesity, education level and amount of physical and cognitive activities. Additionally, randomized controlled trials with certain compounds such as lutein, which is enriched in dark leafy greens, have shown that cognition is improved after supplementing with lutein.
“Over 10 years of follow-up, the rate of decline for those who ate the most leafy greens was slower by 0.05 standardized units per year than the rate for those who ate the least leafy greens. This difference was equivalent to being 11 years younger in age, according to Morris.”
Do we know how the 0.05 standardized units to 11 year conversion is calculated?
If you understand statistics, here is the author’s statistical analysis on the full text page: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5772164/ She does point out that “The study results do not prove that eating green, leafy vegetables slows brain aging, but it does show an association,” Morris said. “The study cannot rule out other possible reasons for the link.”