Dr Laurie Butler is a senior lecturer within the School of Psychology and Clinical Language Sciences. One of his research interests concerns the link between nutrition and cognition.
Over the last five years I have been lucky enough to have been working on research which lies at the boundary between modern psychology, neuroscience and biochemistry. The question itself is a deceptively simple one – to what extent can nutrition slow or even reverse cognitive decline?
In my blog I hope to give you a sense of some of the issues, findings and challenges involved.
Factors affecting likelihood of cognitive decline
We know that there are a host of factors which influence our rate of cognitive decline. Aside from age, we know that IQ as a child and education levels are important predictors, as are various socio-demographic and genetic factors. Interestingly, we also know that cardiovascular function and physical fitness are important as is keeping mentally fit (eg doing crosswords, sudokus etc.). What is becoming increasingly apparent though is that what we eat and drink is important too. I’m going to focus here on Omega 3 fatty acids and flavonoids.
Omega 3 fatty acids
Omega 3 fatty acids found in large quantities in oily fish are frequently in the news and a lot of people take fish oil supplements. Omega 3 fatty acids are interesting because they are highly concentrated in the brain and they have anti-inflammatory, antioxidant and neuroprotective properties. Interestingly, although the recommended daily intake for a healthy, non-pregnant adult is around two portions per week (140g per portion), current intake is only 0.3 of a portion with 70% of adults eating no oily fish at all. Having said that, if everyone on the planet met this recommendation that we would have to double the available fish oil (the topic for another blog…).
What do tea, fruit and vegetables, citrus fruits, berries, red wine and cocoa (among others) have in common? They all contain flavonoids of one type or another. There are over 6,000 different flavonoids, a number of which have been shown to cross the blood brain barrier, affect proteins involved in neuronal growth/survival, and stimulate new neurons. We do a lot of work on flavonoids here at Reading – for example, if you read a report in the media on blueberries and cognitive performance it is likely to be us!
Measuring cognitive function
At its simplest, as psychologists we ask whether intakes of omega 3 or flavonoids have an effect on cognitive function. How do we do this though? One relatively quick way is to use a global measure of cognitive function. One example is called the Mini Mental State Examination or MMSE which poses a series of short questions on language, memory and orientation. However, it is not really very sensitive – it might help to determine if someone has pathological cognitive decline but is not so sensitive to decline in the normal range.
So you need to use more sensitive tests for age-related decline. The good news is that some cognitive functions such as general knowledge, verbal ability and some numerical abilities are relatively preserved as we age. However, some cognitive functions are more sensitive to decline than others. For example, speed of processing (ie the speed at which cognitive functions can be carried out) actually starts to decline in your 30s.
OK so we have our nutrients and we have some cognitive tests – what do we do next? Well there are two major types of experimental design. The first is an observational design, whereby, for example, I might invite a large group of people to complete a questionnaire designed to assess dietary flavonoid levels and measure cognitive performance. The problem with this sort of design is that you cannot say anything about cause and effect (ie that flavonoids are definitely causing the improvement in cognition). To do this you need to use a randomised controlled trial design (RCT) whereby some people are allocated to a control condition and some to your nutritional intervention condition.
So how good is the available evidence for the effects of flavonoids and omega 3 fatty acids on cognition? Well at the moment it seems to depend on the type of design you look at.
For observational designs, there is some really compelling data. For example, a Norwegian study by Nurk et al (2007) showed that older adults with a higher daily fish intake (up to around 80g per day). displayed better cognitive performance relative to those with lower fish intake. Similarly, for flavonoids, Letennuer et al (2007) found that a group of older adults with the highest flavonoid levels in their diet (up to 36mg) showed the best MMSE outcome at baseline and also showed the slowest cognitive deterioration over a ten-year period.
However, when using randomised controlled trial designs, the evidence gets more patchy. Of the available omega 3 fatty acid studies, most have failed to detect effects on cognitive function in healthy or abnormal aging to date. For flavonoids, there is some RCT evidence of benefits, particularly the benefits of blueberries on pre-dementia patients (Krikorian et al 2010). In our work, we have shown some beneficial effects of single acute doses of cocoa and blueberries on cognitive performance in both young and older adults.
So as far as flavonoids and omega 3 fatty acids are concerned the jury is out…more data needed.