Monday May 18 2015
Orange juice is rich in flavonoids
"Drinking orange juice every day could improve brain power in the elderly, research shows," the Mail Online reports. Despite the encouraging words from the media, the small study this headline is based on does not provide strong evidence that an older person would see any noticeable difference in their brain power if they drink orange juice for two months.
The study involved 37 healthy older adults, who were given orange juice or orange squash daily for eight weeks before switching to the other drink for the same amount of time. The 100% orange juice contains more flavonoids, a type of plant compound that has been suggested to have various health benefits.
The researchers gave participants a whole battery of cognitive tests before and after each eight-week period. Both drinks caused very little change on any of the test results and were not significantly different from each other on any of the tests individually.
The researchers also carried out analyses where they combined the test results and looked at the statistical relationships between the drink given and when the test was given. On this occasion, they did find a significant result – overall cognitive function (the pooled result of all the tests combined) was better after the juice than after the squash.
But the overall pattern of the results doesn't seem very convincing. This study does not provide conclusive evidence that drinking orange juice has an effect on brain function.
Where did the story come from?
The study was carried out by researchers from the University of Reading, and was funded by Biotechnology and Biological Sciences Research Council grants and the Florida Department of Citrus, also known as Florida Citrus.
Florida Citrus is a government-funded body "charged with the marketing, research and regulation of the Florida citrus industry", a major industry in the state. Florida Citrus was reported to have helped design the study.
The study was published in the peer-reviewed American Journal of Clinical Nutrition.
The Mail Online took the study at face value without subjecting it to any critical analysis. Looking into the research reveals rather unconvincing evidence that drinking orange juice would have any effect on a person's brain function.
What kind of research was this?
This was a randomised crossover trial that aimed to compare the effects of 100% orange juice, which has high flavanone content, and orange-flavoured cordial, which has low flavanone content, on cognitive function in healthy older adults.
Flavonoids are pigments found in various plant foods. It has been suggested they have various health benefits – for example, some studies have suggested that high consumption of flavonoids can have beneficial effects on cognitive function. Flavanones are the specific type of flavonoids found in citrus fruits. This trial investigated the effect of flavanones in orange juice.
This was a crossover trial, meaning the participants acted as their own control, taking both the high and low flavanone content in random order a few weeks apart. The crossover design effectively increases the sample size tested, and is appropriate if the interventions are not expected to have a lasting impact on whatever outcome is being tested.
What did the research involve?
The study recruited 37 older adults (average age 67) who were given daily orange juice or orange squash for eight weeks in a random order, with a four-week "washout" period in between. They were tested to see whether the drinks differed in their effect on cognitive function.
All participants were healthy, without significant medical problems, did not have dementia and had no cognitive problems. In random order, they were given:
- 500ml 100% orange juice containing 305mg natural flavanones daily for eight weeks
- 500ml orange squash containing 37mg natural flavanones daily for eight weeks
The drinks contained roughly the same calories. The participants were not told which drink they were drinking, and the researchers assessing the participants also did not know.
Before and after each of the eight-week periods, participants visited the test centre and had data collected on height, weight, blood pressure, health status and medication. They also completed a large battery of cognitive tests assessing executive function (thinking, planning and problem solving) and memory.
The researchers analysed change in cognitive performance from baseline to eight weeks for each drink, and compared the effects of the two drinks.
What were the basic results?
On the whole, the two drinks caused very minimal change from baseline on any of the individual tests. There was no statistically significant difference between the two drinks when comparing score change from baseline on any of the tests individually.
There was only a single significant observation when looking at the individual tests at the end of treatment (rather than change from baseline). A test of immediate episodic memory was higher eight weeks after drinking 100% orange juice compared with squash (score 9.6 versus 9.1). However, when this was compared to the change from baseline, it didn't translate into any significant difference between the groups.
The researchers also carried out a statistical analysis looking at the interactions between the drink given and the testing occasion. In this analysis, they did find an interaction between the drink and testing for global cognitive function (when all test results were combined). This showed that, overall, this was significantly better at the eight-week visit after the orange juice intake.
How did the researchers interpret the results?
The researchers concluded that, "Chronic daily consumption of flavanone-rich 100% orange juice over eight weeks is beneficial for cognitive function in healthy older adults."
They further say that, "The potential for flavanone-rich foods and drinks to attenuate cognitive decline in ageing and the mechanisms that underlie these effects should be investigated."
Overall, this small crossover study does not provide conclusive evidence that drinking orange juice has an effect on brain function.
A wide variety of cognitive tests were performed in this study before and after the two drinks (orange juice and squash). The individual test results do not indicate any large effects. Notably, both drinks caused very little change from baseline on any of the test results, and were not significantly different.
The only significant results were found for overall cognitive function when combining test results and looking at statistical interactions. The fact a consistent effect wasn't seen across individual measures and the different analyses means the results are not very convincing.
The trial is also quite small, including only 37 people. These participants were also a specific sample of healthy older adults who volunteered to take part in this trial, and none of them had any cognitive impairment, so the results may not be applicable to other groups.
While the participants were not told what they were drinking and the drinks were given in unlabelled containers, they did have to dilute them differently. This and the taste of the drinks may have meant the participants could tell the drinks apart. The researchers did ask participants what they thought they were drinking, and although about half said they did not know, most of those who gave an opinion (16 out of 20) got it right.
There is also only comparison of high- and low-flavanone orange juice. There is no comparison with a flavanone-free drink, or foods or drinks that contain other types of flavonoid.
The possible health benefits of flavonoids or flavanones specifically will continue to be studied and speculated. However, this study can't conclusively tell us that they have an effect on brain power.
A good rule of thumb is what's good for the heart is also good for the brain – taking regular exercise, eating a healthy diet, avoiding smoking, maintaining a healthy weight, and drinking alcohol in moderation.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.