Friday November 30 2012
Green tea contains over 200 bioactive compounds
“Looking for a morning brain boost? Forget coffee – green tea holds the key for men”, suggests the Daily Mail.
Earlier this month we were told that green tea helps prevent bowel cancer, now new research suggests it could aid memory and cognition (thinking ability).
This headline stems from a small study involving brain scans on 12 healthy males. The researchers were using a type of scan known as functional magnetic resonance imaging (fMRI), which provides a real-time continuous scan of blood flow inside the brain. The idea underpinning fMRI is that increases in blood flow in certain areas of the brain correspond to neural activity.
The researchers found that drinking a soft drink laced with green tea extract appeared to increase blood flow to a part of the brain called the dorsolateral prefrontal cortex (DLPFC). The DLPFC is thought to be involved in cognitive tasks such as long-term memory, reasoning, and comprehension.
However, it also showed that this did not affect performance in a working memory task that volunteers performed each time their brains were scanned.
The headline “forget coffee – green tea holds the key for men”, is an eye-catching, but misleading, extrapolation of the results of this study. However, reporting that soft drinks containing green tea may cause small changes in blood flow in the brain (as was actually measured in the study), but do not seem to help in performing memory tasks, was perhaps seen as less headline-worthy.
Where did the story come from?
The study was carried out by researchers from Swiss and German Universities and was funded by the University of Basel and grants from Rivella Ltd, Rothrist, Switzerland.
Rivella is a Swiss company that produces drinks, including what their website describes as “wellness beverages” created from a “secret blend of herb and fruit essences”.
One drink reportedly contains “stimulating green tea extracts”.
The study was published in the peer-reviewed European Journal of Clinical Nutrition.
Due to the funding coming from a drinks company whose products contain green tea extracts, there is the potential for a conflict of interest that would favour positive findings toward green tea to increase sales. However, this may not be the case, as the authors explicitly declare, “the sponsor of the study had no role in the study design, the collection, analysis, and interpretation of data, the writing of this report, or in the decision to submit the paper for publication”.
The Daily Mail’s reporting of this story over-egged the significance of the research, as they did not emphasise that there are only limited conclusions you can draw from a study that scans the brain functions of just 12 men.
Much of the reporting into studies involving functional magnetic resonance imaging has fallen into a similar trap. While changes in blood flow may be indicative of certain types of neural activity, they cannot provide definitive proof that this is the case. Similarly, it is often not clear if, or how, these small changes in blood flow are related to actual behaviour or cognitive performance at various tasks.
What kind of research was this?
This was a double blind, placebo controlled laboratory study that scanned the brains of men to examine the neural effects of drinking green tea extract (or placebo) on their brain activation and while performing a memory task.
The researchers state that green tea is being recognised as a beverage with potential beneﬁts for human health and cognitive functions. They cite a number of previous human studies, which they say, provide preliminary evidence that green tea intake may have a positive role in improving effects on cognitive functions.
What did the research involve?
The study analysed 12 healthy male volunteers aged 21 to 28.
The men were first given test drinks, then asked to perform tasks known to use working memory. Their whole brains were scanned, but the researchers also focused in on a specific area of the brain they were interested in, called the dorsolateral prefrontal cortex (DLPFC), a key area that mediates working memory processing.
The study used two types of commercially available drink provided by Rivella. The first was a carbonated milk-whey based soft drink known as variety “C” which acted as a control drink. The second variety “G” was very similar to C but also contained green tea extract. Volunteers were given either 250ml or 500ml of the drinks via a feeding tube directly into their stomach (the 250ml amounts were diluted to 500ml so the participants couldn’t guess their treatment).
The two amounts were used to see if there were any dose-related effects.
Each man received all the drinks (Variety C at 250ml and 500ml and Variety G at 250ml and 500ml) sequentially across four separate sessions, but the sequence in which they were given the different drinks was different.
Both the men and those administering the drink were blinded to the treatment allocation.
Shortly after being given the drink, the brain activity of the volunteers was scanned using functional magnetic resonance imaging (fMRI), while the volunteers performed a working memory task. fMRI measures tiny blood flow changes in the brain that are related to its activity.
In the task, known as the “n-back task”, subjects were presented with a series of letters and required to indicate via a button press whether each letter was the same as one presented previously in the sequence – whether the letter had also appeared one, two or “n” letters back in the sequence.
The analysis compared the effects of the different drinks (variety C vs. G) and amounts (250ml vs. 500ml) on the brain activity and task performance of the men.
Participants were told to abstain from any substance use for the duration of the study, and from the intake of alcohol, caffeine, green tea products and citrus juices for up to 24 hours before each study day.
Volunteers, who regularly use green tea or green tea products, or took any regular medication including over-the counter drugs, had ever used any illicit psychotropic substances, who consumed four to five units of alcohol daily or 20 units per week, or had any psychiatric, neurological or severe medical illness history were excluded.
What were the basic results?
The whole brain analysis showed no significant differences in brain activity (measured by fMRI) or task performance between the men consuming the two different drinks, or different amounts of the drinks. In fact, there was no difference in task performance even when they focused on the DLPFC area of the brain only.
However, there were some statistically significant findings reported for brain activity differences. Compared to giving 500ml of the control drink, 500ml of the green tea increased brain activation in the specific areas of the brain called the middle frontal gyrus and inferior parietal lobule.
When looking specifically at brain activity in the DLPFC region, the researchers found that those given 500ml of the green tea containing drink had “significantly increased” brain activation in both the left and right sides of the brain than those given 250ml.
How did the researchers interpret the results?
The researchers concluded that their results “suggest that green tea extract may modulate brain activity in the dorsolateral prefrontal cortex, a key area that mediates working memory processing in the human brain”.
This small study involving functional brain scans on 12 healthy males showed that drinking a soft drink laced with green tea extract might affect activation in the specific area of the brain involved in working memory (dorsolateral prefrontal cortex). However, it failed to show this influenced performance in a working memory task, this might have been because the study was too small to detect a difference in task performance.
This study is useful for researchers interested in understanding the potential influence of green tea extract on activity in the brain. However, an issue with any study of this type is the difficulty in linking small changes in brain activity to any appreciable difference in a person’s behaviour or performance in a task. Until further research explores this link, the immediate implications of this research to the average morning coffee or green tea drinker are minimal.
A further limitation of this study was that green tea extract was consumed via a soft drink rather than a pure extract. While a pragmatic effort was made to choose two very similar drinks, one with and one without green tea extract, using a pure extract would have better isolated its potential effect.
As far as the headline, “forget coffee – green tea holds the key for men” is concerned; this is a pretty generous extrapolation of the results of this study.
Changes to blood flow inside the brain does not automatically correspond to you suddenly becoming smarter or having a better memory. Further research would be needed to see if these sorts of brain activity changes are in any way related to memory or other cognitive performance.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.