|The latest demon drink.|
A few weeks ago I wrote a post on a recent news meme concerning biological markers for teen depression, found here. This week the alarm bells are ringing again, linking teen consumption of caffeinated energy drinks with depression, sensation-seeking behavior, and substance use.
The source is an article recently published in Preventive Medicine by Azagba, Langille, & Asbridge (reference below).
My concern here is not the nature of the study itself, which included appropriate cautions about the interpretability of the data. It is about the way that studies are seized upon by media for maximum effect, obscuring and in some cases contradicting the actual content of the science on which they are supposedly reporting.
The study is an analysis of data from the 2012 Student Drug Use Survey, and examines associations with energy drink use among 8210 Atlantic Canada high school students.
Sure enough, the authors found a relationship between the consumption of energy drinks, positive replies to questions suggesting a sensation-seeking personality, self-reported symptoms of depression, and the use of other substances. The survey was a one-time measurement, so no data were available on factors predicting the subsequent emergence of other factors.
This is a classic correlational study that sharply limits the ability to make causal inferences. Given two variables, A and B, that seem to correlate, A might cause B, B might cause A, or some other variable C might cause both A and B.
“Correlation is not causation” are perhaps the most frequently-uttered four words in all of introductory statistics classes. But frequently-uttered is not, it seems, frequently-remembered. You could make a parlour game in which participants race to find violations of this principle in any given issue of your average newspaper.
At first, it might have seemed that we were going to get some sober reporting out of this study:
- “Study finds energy drink consumption linked to depression, substance abuse in teens” says Global News.
- “Report links teenage energy drinks with substance abuse” announces eCanada Now.
- “Teen energy drink consumption linked to depression and substance abuse” reports the Hamilton Spectator.
Okay, there’s some fairly hefty implying being done in all of these headlines, but look carefully and we see the word “link” over and over, indicating a relationship but one without a directional arrow. But let’s not stop there.
- “Could energy drinks increase the risk of depression in teens?” asks Science World Report futilely – a question to which the answer would have to be “God knows, but this study sure can’t tell us.”
- “NS (Nova Scotia) teens on alert after energy drink study finds links to depression, substance abuse” hyperventilates Global BC, neglecting to display photographs of the apparently alarmed teens.
And my favorite:
- “Beware – energy drinks can lead to heart problems in teens” screams the Health Site at India.com – an article that actually does focus on the Canadian study, which has nothing, really nothing, to do with heart problems.
Look inside even the more soberly-headlined stories and all awareness of the correlation problem seems to vanish out the window. Suddenly the consumption of energy drinks causes depression, substance abuse, and depression. Most articles raise the issue of limiting access to these drinks for teens, and about half of most articles is devoted to public policy implications.
In the Global BC story, for example, we read this: "Doctors (in) Nova Scotia say the study is more proof something needs to be done to protect teens against energy drinks. Kevin Chapman, the organization’s director of health policy, wants legislation to restrict the sale of energy drinks to people younger than 19."
Unfortunately, there are no public policy implications from this study, as it says nothing whatsoever about causality.
Let's try a little thought experiment. Imagine a game in which four contestants are each handed one of the four linked variables (depression symptoms, sensation seeking, substance use, and energy drink use) and each has to come up with a narrative in which their variable causes the others.
All four have a good chance at the trophy – and the one who gets “energy drink consumption” is probably in the worst position. Let’s look at the possibilities for the other three just with regard to energy drink consumption:
Depression as root cause. Depressive states tend to bring on sleep troubles, which tend to result in daytime sleepiness. Energy drinks and other caffeinated beverages are advertised and sold as antidotes to sleepiness, so depressed teens looking for greater cognitive sharpness and alertness are likely to seek them out. It would be a surprise to learn that depressed teens didn't try energy drinks more than others.
Sensation seeking as root cause. Sensation seekers tend to be easily bored, and high school is easily boring. The result is often an inability to focus, which can be countered temporarily by caffeine. As well, the drinks, being psychologically active, produce a sensation. Unsurprisingly, sensation seekers will seek that sensation more than non-sensation-seekers. Oh, and in case we see a link between sensation seeking and attention deficit disorder, how do we help kids with ADD focus? Stimulants. And what is caffeine again? Right.
Substance use as root cause. Substance users tend to a) stay up late, which results in daytime sleepiness, and b) use alcohol, which produces sleepiness in the acute phase and sleep disruption afterward. And how do people in this society combat sleepiness? Often, with caffeine. As well, teens tend to prefer sickly-sweet alcoholic libations, and few substances are as sickly sweet as energy drinks.
Notice, please, that I’m not saying that using energy drinks is a good idea. For one thing, they’re loaded with sugar. A can of Red Bull has 110 calories, a can of Monster Energy 100 calories – almost as much as soda pop. Coincidentally, the World Health Organization has just slashed their recommendations for daily dietary sugar to less than the amount in a single can of Coke - a move that seems consistent with the evidence.
I’m simply saying that there are alternative explanations for the association between the use of energy drinks and these other variables that have nothing to do with energy drinks causing depression, substance abuse, or sensation seeking.
Two other observations stand out...
First, energy drinks are hardly the only source of caffeine out there. Red Bull contains about 80 mg of caffeine per can, and Monster Energy has 140-160 mg. Both are less than the caffeine content of a 10 oz. (Starbucks tall) cup of coffee. Red Bull’s total is about equivalent to a largish cup of black tea. But we don’t hear panicked reports of high school students mainlining tea out behind the gym. And none of the reports suggest that high school students should be barred from purchasing tea and coffee, as well as energy drinks. (Though given a forced choice, I’d give them a cup of tea rather than a Red Bull, given the sugar content of the latter.)
Second, no one comments on the actual consumption figures found in the study. The authors report that 62% of students reported consuming at least one energy drink in the past year, and (just) 20% reported use once or more per month. Fully 80% of students, then, denied any consistent use of energy drinks, and 38% had virtually no consumption of them at all. If we could get figures for soda pop down this low we’d be dancing in the streets.
We’re used to the “Have you in the past month used…” question from other drug studies, but let’s face it: There’s a difference between using heroin once in the past month and saying the same of an energy drink. If a teen came into my clinic and said “Well, I have tried energy drinks, but I only consume about one a month” I’d wave it off. If that’s the worst story this kid has to tell, he’s doing pretty well, about like the one who guiltily confesses a seasonal trip to Starbucks.
So should we be banning the purchase of energy drinks by minors?
Well, why? If we’re worried about the caffeine, then let’s ban the tea that parents happily serve their kids. If we’re worried about the sugar, then let’s ban soft drinks. (Actually, I could get behind that one, believing as I do that routinely serving soft drinks to kids is a form of child abuse.) If it’s some other component of energy drinks that concerns us, then let’s have some research verifying (or at least suggesting) damaging effects.
If we’re worried that somehow energy drinks lead to depression, then let’s do some research bearing out that link. Maybe an experimental study is difficult to imagine (“Here, you kids drink water and you other kids drink Red Bull for a year…”), but a naturalistic study of usage and mood over time is not beyond us.
Do we, perhaps, imagine that energy drinks change kids’ personalities and turn them into sensation-seekers? It’s hard to see how this would work – at least not any more than any other part of our ephemera-obsessed culture.
Or are we worried that energy drinks lead to the abuse of other substances? Great, we’re back on the “slippery slope” argument that worked so well for marijuana. Maybe we should be on the lookout for “gateway drugs” that lead to energy drinks, which in turn lead, one supposes, to crack. Oolong, perhaps? Earl Grey? Or, more likely, Coca Cola?
Maybe before we start issuing or even suggesting public policy, we should conduct the research to determine whether our ideas are fully or only half-baked. Science can be a helpful guide to policy, but only if used wisely. Treating findings as Rorschach cards from which to free-associate is only likely to lead us in unhelpful directions.
Read it Yourself
Azagba, S, Langille, D, & Asbridge, M (2014). An emerging adolescent health risk: Caffeinated energy drink consumption patterns among high school students. Preventive Medicine, 62, 54-59.
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