Do flavonoids really benefit the brain?

What so-called “superfoods” tend to have in common is a high concentration of flavonoids, Katie Barfoot from Reading University told Eva Higginbotham....

Katie - There are a multitude of foods that are good for your brain in terms of brain development, cognition, so your cognitive abilities, and your mood as well. And my specific research looks into flavonoids and whether they are good for the brain or not. Flavonoids are compounds that are found naturally in high levels in foods such as fruit and veg, teas, chocolate, red wine. Flavonoids have actually been found to exert positive effects on our brains, specifically in areas such as memory and also in executive function domains as well. So abilities like planning, working memory, and the ability to kind of self-regulate, organise as well. So they seem to be really beneficial taken in the short term and in the long-term as well.

And the reasons behind this we think are because of mechanisms related to blood flow. We know flavonoids can improve cardiovascular function. So they actually dilate blood vessels, which in turn decreases blood pressure. We know that this is the case specifically after consuming things like cocoa, orange juice, green tea, cranberry, blueberry - that are high in flavonoids. And we think this improved cardiovascular function can actually extend to the brain and increase blood flow to specific regions of the brain that's involved in kind of cognitive function or mood as well.

Eva - What sort of experiments can you do to test whether or not flavonoids or other things might be good for the brain?

Katie - There are two kinds of methods nutritional science uses to look at this question. The first is where we look at epidemiological data - the frequency in the patterns between variables across a population. So this often includes a large number of participants. We find that those who consume a high amount of flavonoids seem to have the most protection from cognitive decline. So in terms of older adults, they have a natural decline in memory as they get older. And we find that flavonoids seem to protect against that decline. Epidemiological data is more focused on the correlation, so the kind of relationships and the links between variables, rather than more cause and effect. We can't control for specific dosages or lifestyle factors in this type of data collection. And we do control for those things in intervention trials. This is mostly what our lab at Reading focuses on running.

You recruit a set of participants. So usually these are from a similar background and a similar age with similar health status. Split the group in two, and you assign one of them the intervention that you want to give them, and you assign the other group a placebo as closely matched to the intervention as possible, but it does not contain any flavonoids. We can then compare across the groups and across time to see if there are any differences before and after consumption of the flavonoid foods.

Eva - What do you find in those studies?

Katie - In cognitive trials, we tend to look at acute and chronic relationships. So the acute period is in the one to six hour post consumption. The chronic literature looks more at what is happening after daily supplementation of a flavonoid. So eating that chocolate bar every day for 30 days, for example. So what we find in the chronic literature - improvements in memory. Specifically in older populations, we see a prevention of memory decline, kind of maintenance of memory in a flavonoid group in comparison to a placebo group. We also see improvements in executive function as well. Acutely, we do see improvements in psychomotor performance, improved visual-spatial ability, improved kind of reaction times. And we also see improvements in working memory as well. And improved episodic memory as well, so remembering certain events or certain kind of points in time.

Eva - The chronic study sounds like my kind of study - eat a chocolate bar every day for 30 days. Thank you very much! How do you untangle the stuff that's in the chocolate bar and the flavonoid? So a chocolate bar of course contains a lot of sugar. Could you not just give people a flavonoid pill or is there something about it being food that's important?

Katie - Yeah. Now this is really interesting. This is something that the field is kind of investigating, you know, as an ongoing thing, really. We do match the intervention and the placebo food, you know, as much as we can. So for example, you're saying about sugar there. Yes. We know sugar affects the body. Sugar does affect the brain as well. So could it be the sugar? The fact that we have the same chocolate bar in the placebo group minus those flavonoids is a nice control. So we can say that it can't be the sugar if we're seeing an increase in the flavonoid group, it must be those flavonoids. Because that's the only thing that's different between the two groups.

Eva - So apart from improving cognition and memory, are there any other effects that flavonoids could be having?

Katie - The field has kind of moved towards investigating the effect of flavonoids on mood. And this is a relatively new area and there has been some primary research that has shown effects. So some research that I conducted with Sundus Khalid, we found that after a blueberry intervention children and also young adults showed improvements in their positive mood. So kind of how they felt on a scale of positive and negative mood items. And we've seen that also as well in recent unpublished data that I've conducted looking at mood in a sample of postnatal mothers as well. My kind of research prerogative is to now look at relationships between mood and flavonoids in populations that are potentially at risk of mood disorders.

Eva - Could you look directly at the brain to try and figure out what the cause and effect is?

Katie - There's quite a few studies scanning the brain using MRI, and also using functional MRI as well which is where you kind of look at the brain in real time to see what it's doing in response to you performing a task for example. Some studies do suggest that there is increased activation in areas associated with the tasks that the participants are performing. But actually the waters are a little bit muddy here in terms of whether those increases in brain activation are actually linked to increased behavioural outcomes as well. So in the studies that have been done on this, we see activation of certain brain regions without emergence of behavioural effects. So it may just be that these increases in activation may just be reflecting cognitive effort, increased concentration to actually perform the task, without actually being better at the task. So the research has still got a way to go in terms of trying to figure out what this dissociation between the two actually means.

Eva - It sounds like it's a really complicated field to untangle the emotional response we might have when we eat something we like versus the stuff that's actually in the food, versus maybe if you're a new mum, having time to sit down and actually enjoy something and having that momentary break and how that might affect your mood. What can we really conclude at this stage?

Katie - There is a lot of research out there that suggests flavonoids are beneficial for the brain in terms of they improve cognitive function or they prevent cognitive decline in older adults. You know, the emerging research on mood at the moment suggests that they may play a part in maintaining positive mood or improving positive mood in certain populations. And we can say that quite confidently from the trials that have been conducted over the last 20 or so years. So the key message in terms of flavonoids is to try and include them in your diet where you can really. And the data suggests that a higher level of flavonoid consumption in your diet across your lifetime will see you have better memory performance and less kind of cognitive complaints as you get older.

Eva - There are some things that are in high flavonoid foods though, like red wine, you said, or tea has caffeine or chocolate has sugar, that might have other effects that we're not such big fans of. Is there a reason that we can't just make a flavonoid pill?

Katie - The research to date suggests that potentially it's down to interactions in the whole food rather than the flavonoid specifically that may be kind of exerting these beneficial effects. So I know there has been some research that has looked at say, you know, a whole blueberry versus the specific flavonoid extract found in blueberries called anthocyanins. And we don't find the same effects. So it may be that actually it's the flavonoids within the other constituents of the food - so such as fibre and vitamins - interacting within our body that may produce those beneficial effects. And that is something that needs to be investigated further in the field.