Consider this slightly cumbersome headline in the last Saturday’s Daily Mail, located in the newspaper’s Health section: “Take time for tea and give your brain a lift as well as reduce tiredness”. The story refers to a new research paper published in the journal Nutritional Neuroscience. Based on the research, the Daily Mail reports that having a cup of tea “could help you solve the crossword faster” and “can improve brain power and increase alertness”. According to the Mail, tea also “reduced tiredness among the volunteers.” As with many such stories, the original research is far more complex than can be captured by a 300-word newspaper story. Nonetheless, we might expect professional newspaper journalists to consider the subject just a little bit more rigorously than is done here.
In the study, the researchers tested cognitive task performance in 44 young adults across two occasions. Before one trial, they were given a tea-laden drink; before the other, they were given a placebo (i.e., tea-free) equivalent. On neither occasion did the participant know which drink they were receiving. At the end of the study, the researchers found that cognitive test scores and mood levels were higher when testing took place after the drinking of tea.
One problem for journalists in reporting such studies is that the findings are very hard to generalize beyond the immediate research context. For example, it is difficult to extrapolate from peculiar cognitive laboratory tasks to everyday activities performed in real-world settings (such as doing crosswords). For one thing, the study tasks were specifically designed to test people’s capacity to switch attention rapidly from one target stimulus to another. This is just about the opposite of what happens when people do crosswords, a pastime that involves reflective contemplation rather than constant attention-switching. Doing crosswords well also requires background knowledge, a good vocabulary, a knack for mental imagery, and (probably) past experience of doing crosswords, none of which were examined by the researchers. As such, it is unclear whether the Daily Mail’s conclusion that a cup of tea can help you solve crosswords is at all reasonable.
Of course, we might give journalists a certain amount of leeway on these points. After all, it can be a struggle to come up with a reader-friendly example of an everyday attention-switching task. However, does this study actually show a true effect for tea-drinking on attention-switching? Well, not very clearly.
One of the biggest problems with researching the effects of caffeine on cognitive performance is that the vast majority of participants will be habitual caffeine consumers. As caffeine has addictive properties, any cessation of caffeine consumption (as might be required by a study) will precipitate a range of withdrawal effects. When these people are deprived of caffeine, they become ratty, irritable, and unfocused; when they are provided with caffeine, these symptoms disappear.
Participants in the Daily Mail study were required to abstain for caffeine for a whopping 12 hours prior to cognitive testing. By the time these poor unfortunates were in the laboratory, they would have been suffering a wide range of unpleasant withdrawal symptoms. When given a placebo, not much would have changed; however, when given a tea-drink, their mood, energy levels, and concentration would have immediately improved.
According to some researchers, this whole process accounts for the entirety of caffeine’s reputation as a mood-boosting and attention-enhancing food ingredient. While caffeine often seems to boost mood and concentration, in actuality all caffeine does is reverse the misery-inducing effects of caffeine withdrawal. This interpretation, referred to as the withdrawal-reversal hypothesis, has been corroborated by a range of research studies specially designed to test it (for example, studies that look at different dosages of caffeine, different regimes of withdrawal, and comparisons across coffee drinkers who are at different levels of addiction).
Other investigators have attempted to debunk the withdrawal hypothesis by comparing caffeine’s impact on caffeine consumers against its impact on non-consumers. However, such studies involve administering tea and coffee to people who never ordinarily drink them. As well as the fact that caffeine tastes harshly bitter to first-time consumers, it is very unclear whether non-consumers are representative of the population at large (some 80% of whom consume caffeine on a daily basis). By analogy, nobody would ever suggest that a good way to test the effects of habitual alcohol consumption on crossword-solving would be to ply non-drinkers with liquor before getting them to do attention-switching tasks in laboratories. Overall, it is difficult to say whether comparing tea drinkers and non-drinkers offers a valid test of the caffeine withdrawal hypothesis.
But maybe an expert opinion might help. The Daily Mail story (and, presumably, the original press release) includes a quote from a representative of a group called the Tea Advisory Panel. He summarizes his reasoning as follows: “[These] studies provide evidence that consumption of black tea improves cognitive function, in particular helping to focus attention during the challenge of a demanding mental task…As a result, all this new data adds to the growing science that drinking tea, preferably four cups of tea a day, is good for our health and well being.”
Note how the spokesperson’s reasoning skips a step during this statement. Effectively, he asserts that because the lab findings “show” a link between tea and performance on attention-switching tasks, this implies a positive effect for caffeine on “health and well being”. Now even if interpreting the original research findings was straightforward (which it isn’t), they would not in any way support such a conclusion. This is because — even with the most broad-sweeping perspective on such matters — the capacity to suddenly focus your concentration is an extremely weak indicator of overall health and well-being. After all, consuming cocaine might help you perform cognitive tasks better in a laboratory setting; but would such a finding “add to the science” that snorting coke is good for your “health and well being”?
We should note that the Tea Advisory Panel is actually funded by the caffeine industry, as was the research study reported by the Daily Mail. So why is the caffeine industry interested in both funding and promoting research that highlights the purported advantages of consuming tea? Surely, with 80% of the world’s population already consuming caffeinated beverages on a daily basis, their marketing departments can take the rest of the day off? Well, tea manufacturing might be a bit more capitalistic than is commonly appreciated. The production and sale of caffeine products is a multi-billion dollar global corporate activity, which in commercial terms is worth nearly as much as the oil industry. Globally, over 2.25 billion cups of coffee are consumed each day: based on a rough estimate of $1 per cup, this yields a potential $0.82 trillion of indicative turnover to the industry each year.
These are high stakes, and it is thus important to the industry that positive messages dominate over negative or neutral ones. The common belief that caffeine boosts both mood and concentration (which is really achieved by undoing the side-effects of caffeine withdrawal, most acutely felt after a night’s sleep) is intrinsic to its brand identity. Accordingly, it is in the industry’s commercial interests to promulgate such findings as widely as possible, while ensuring that any complexities in the picture (such as methodological limitations or interpretational ambiguities) are kept well away from the reader’s eye.
This news story describes research conducted by employees of Unilever — which manufactures and sells several major caffeine products — for which the only additional commentary presented is sourced from the Tea Advisory Panel — which is an industry-backed group. It is no surprise whatsoever that its take-home message tells us that “caffeine products are a good thing”. In fact, the article is basically telling us that people should go out and buy more caffeine products! NOW! In other words, this is advertising, not news.
Not really my cup of tea…
Brian Hughes is an academic psychologist and university professor in Galway, Ireland, specialising in stress, health, and the application of psychology to social issues. He writes widely on the psychology of empiricism and of empirically disputable claims, especially as they pertain to science, health, medicine, and politics.