We are fond of discussing the benefits of vegetables in the nutrition blog! This week we are highlighting a new US study published in Neurology that examines the association between consuming leafy green vegetables and a slower rate of brain ageing.
This was a prospective study (a study that follows people over time) of 960 participants in the Memory and Ageing Study. Participants included in this study (free from dementia at enrolment, average age 81 years,74% female, 95% white ethnicity) completed a food frequency questionnaire and had two or more cognitive assessments over an average follow-up period of 4.7 years. With regards to green leafy veg, the questionnaire asked how often and how many servings people ate of spinach, kale or greens (1 serving = ½ cup) or lettuce (1 serving = 1 cup).
Eating Around 1 Serving Of Green Leafy Veg Per Day Was Associated With Slower Cognitive Decline
The study divided the participants into quintiles (5 groups) based on their green leafy vegetable intake and compared the cognitive assessments of those who ate the most (an average of about 1.3 servings per day) and those who ate the least (around 0.1 servings per day). Adults who were in the top 20% of consumption tended to have slower cognitive decline over time, which the researchers described as “the equivalent of being 11 years younger in age”. The results remained valid after accounting for some of the other factors that could affect brain health, such as seafood and alcohol consumption, smoking, high blood pressure, obesity, education level and amount of physical and cognitive activities.
“Correlation Is Not Causation“
It’s no secret that eating vegetables is good for your health, but unlike as suggested by the headlines reporting on this paper, we cannot say from this study that eating green vegetables could reduce the risk of dementia – rates of dementia were not even measured. And although the study supports other research showing a link between a vegetable-rich diet and a healthy brain, we must always remember the statistics mantra “Correlation is not causation“. Could the adults who ate more green veg in this study also be living more healthy lifestyles in general? While the study did adjust for factors such as education, general physical activity level, smoking, seafood and alcohol consumption, it did not capture every potentially relevant aspect and the study cannot rule out other possible reasons for the link.
There are a number of other limitations:
- The follow-up was fairly short, some people were followed for as little as 2 years, and it can take considerably longer for cognitive decline like memory loss to develop
- This study was small and may be unrepresentative. The voluntary participants on the Memory and Ageing Project may not be representative of the general population of older persons and so generalisability to other populations is unclear
- The food frequency questionnaire is reliant on people’s recall so reports of what foods they ate could be inaccurate and could change over time
- This research doesn’t show that leafy, green vegetables promote brain health any more than other vegetables.
It is actually really difficult to investigate whether a specific food has cognitive benefit. We can’t say with any certainty that leafy green vegetables prevent memory loss, let alone dementia. Nevertheless, the evidence to date is that ‘eating your greens’ is good for health and these types of studies can be extremely useful in giving us an idea of lifestyle factors that are associated with good health. And as the researchers found eating approximately 1 serving a day of leafy green vegetables was linked to slower loss of memory with ageing, why not make sure you include plenty of green veg on the menu – even Brussel sprouts – they are in season.
