Paracetamol and Asthma – Media Reports

September 19, 2008 at 7:40 pm (Bad Science, Media) (, , , , )

I looked at a recent news story about a paper on asthma and paracetamol. According to the Daily Mail Taking paracetamol regularly ‘triples risk of asthma’ and the headline on the Daily Telegraph site is “Paracetamol use found to increase risk of asthma three-fold”.

Given the statement in the first headline (I know it’s in single quotation marks, but really – do they honestly think that single quotes will stop someone concluding that it is definitely the case?) and the Daily Telegraph’s assertion that regular users of paracetamol are nearly three times more likely to suffer from asthma, you might be forgiven for assuming that this is a done deal. After a quick glance at the stories, I took a look at the NHS “Behind the Headlines” take on the coverage of this. The Daily Telegraph’s and the Daily Mail’s assertions are of particular interest given that Behind The Headlines says this:

The study behind this report is a case-control study and by virtue of its design, it cannot prove causation (that paracetamol increases asthma). It also cannot rule out reverse causation (that asthma causes people to take more painkillers). However, when considered alongside the findings of other studies, these results suggest that there may be an association between use of paracetamol and asthma that needs further exploration. This is not a new concern, and researchers have been investigating this for some time.

So while the media reports are implying that causation has been shown, it appears that the Behind The Headlines team (BTH) tell us it would be impossible to do so in a study of this type. I don’t know why the media seem to feel unable to use the phrase “x is associated with y” rather than the inaccurate “x causes y”. Also of interest is the last sentence of the quoted section above – this isn’t new. It’s something that has been looked into for some time now and still needs further investigation, but you wouldn’t know it from the media coverage. I tink the Daily Mail were aware it wasn’t new though.

Weirdly, when I looked through google’s news search the Mail’s report stated that the study was published today in the Lancet. The site had the story down as being updated at 8:21 AM on 19th September 2008, so I assumed the Mail story related to a paper published today in the Lancet. The only thing is, I couldn’t find a Lancet paper on Pubmed relating to asthma and paracetamol from as recently as 2008 – I got a single hit from 2000. BTH has the paper down as being from Eur Respir J 2008, doi:10.1183/09031936.00039208. I think that perhaps what happened was that the Mail updated an old story because they had a new story about paracetamol and asthma. The Mail report that showed up on google news is here. The Mail report on the current study is actually here. Confused? I was. Maybe they should have an ‘originally published’ tag on stories they update, if nothing else it would at least save morons like me from ending up in a state of confusion over what is today’s asthma news and what was 2000’s asthma news. Attempting to understand science stories in the press can be a real pain in the arse sometimes.

Also of interest: The news reports stated that “Paracetamol tripled the risk of asthma”. Given that I have no idea what the chances were of someone having asthma if they haven’t taken paracetamol, I have no idea what it might mean for their chances of having asthma to triple if they do take paracetamol. This is something that Ben Goldacre has raised in his book Bad Science [it’s in chapter 13, if you’re reaching for your copy as you read this]. Newspapers tend to give the scariest/most impressive figures (for example, the relative risk instead of the absolute risk – see here for more on relative v absolute risk). In the case of the media reporting of a Mischief PR press release, there was a statement that there had been a 39% increase in household reports of wasps following introduction of fortnightly bin collections. Perhaps the press should have found the time/space to inform us of the “natural frequency” of asthma attacks, which might mean more to me than being told there is a “tripling of the risk”. Bandolier briefly explains natural frequencies here. Their explanation concludes with this: “Natural frequencies help people to make sound conclusions, whereas conditional probabilities tend to cloud minds”.

Links: Click here for the abstract of the paper.

10 Comments

  1. Claire said,

    I think the Mail has confused the ERS article with the other asthma/paracetamol story currently in the news, the study by Beasley et al which was published in the Lancet. It’s described here . Similar caution applies (cross sectional survey, retrospectively ascertained exposure). There have been suggestions from some commentators, e.g. Professor Scadding in the Independent, that the finding might be explained by the frequency of the viral infections necessitating use of paracetamol rather than the medication itself. But obviously worrying for parents, so one hopes more research will settle this issue.

  2. Claire said,

    Behind the Headlines has now analysed the child asthma – paracetamol story. Their conclusion:

    “…Although it is true to say that this cross-sectional study cannot prove causation on its own, the link and other arguments presented by these researchers suggest that the observational evidence for paracetamol as a risk factor is strong, perhaps strong enough to support their call for urgent research by randomised controlled trials. “

  3. Lesley said,

    Coincidentally I went to a lecture today by a paediatric respiratory physician working with the ALSPAC Study in Bristol where they have similar findings to the Lancet report. We all agreed that firstly it’s very difficult to find any children who have not used paracetamol in infancy, so we need to look at the figures carefully. One Danish study had only 5 children in the non treated group, ALSPAC had 11 children. Secondly it’s quite possible that the children whose parents reported frequent use may have had repeated respiratory symptoms which were related to asthma rather than viral infections meaning that the paracetamol was not causal in the development of asthma, as Glenys Scadding suggested, and thirdly that some objective measure is needed to confirm the findings, as parental reporting of symptoms and medication use is notoriously unreliable. That means we need to think hard about the mechanisms that may be involved, possibly the effect of the reduction of a key antioxidant in the lung during development.
    We know the ISAAC Study is wide ranging and well powered but we need smaller, less epidemiologically based studies to determine if this is a real problem. We also have to bear in mind that there is no real alternative drug that is safe with infants with fever or pain so media hype is really irresponsible in these things. I well remember a couple of years ago with the Serevent issue, the good old Daily Mail’s screaming headline that asthma inhalers were killing children.

  4. jdc325 said,

    Thanks for the comments Claire, Lesley.

    I think that, as usual, the media have been premature with their claims of causality and over-the-top in their reporting.

    I was interested to see the ideas that were discussed at the lecture you attended Lesley. I don’t remember any of the coverage of this study referring to the unreliability of parental reporting of symptoms and medication use, but it’s something that should have occurred to me really – one of those things that I’d probably never have thought of but, when someone else says it, seems obvious.

    Re Serevent – I don’t remember that particular scare, but it wouldn’t surprise me in at all if it was covered in the People’s Medical Journal as “Deadly Inhalers Killing Our Babies”.

  5. Claire said,

    Regarding the salmeterol issue, while the media exaggerate and cause unnecessary panic, there is still some concern about rare – but serious – adverse events. A Cochrane review was published earlier this year – podcast by lead reviewer here. The FDA is due to review this issue again later this year.

  6. Claire said,

    That is a good about about the mainstream media coverage not explaining why factors such as reliance on retrospective reporting by parents mean that the findings of this study need to be confirmed by further research, whereas this point was made by more specialised sources such as BTH or the MedPageToday report linked above. Obviously, health editors think we’re too stupid to grasp the nuances of a large study suggesting that there is possibly something to be concerned about but that futher work is needed before a settled conclusion can be made. Would it be too much to hope for that health editors in the UK might actually think of contacting the BTH team before running such a story? Or alert their readers to the existence of BTH?

  7. jdc325 said,

    “Would it be too much to hope for that health editors in the UK might actually think of contacting the BTH team before running such a story? Or alert their readers to the existence of BTH?”
    I can’t think of any reason for a health editor (or any journalist writing a health story) not to contact BTH for hints on how to report studies such as this one, but I guess BTH only cover stories already published in the media so journos aren’t able to simply click on their website and get the info they want on a specific story (and emailing BTH would probably be too much effort for a journo – if you want an idea of how much fact checking [some] reporters do, check out this on b3ta: Lazy Journalist). Alerting their readers to BTH would be a no-no for any newspaper – they like to think they are the arbiters of truth and that they are the best conduit for health information, despite mountains of evidence to the contrary. It’s a fantasy, but one they seem unwilling to give up.

    “Obviously, health editors think we’re too stupid to grasp the nuances of a large study”
    Yeah – ironically, the media think we’re morons. I like their confidence in their own ability to understand such stories. Although…
    Wiki on Dunning-Kruger. PDF of Dunning-Kruger paper.

  8. Claire said,

    Yes, I think I was having a Pollyanna moment imagining some health journos might pause for expert advice before unleashing garbled interpretations upon their readers. You know, the other night I watched a tv show (my daughter’s choice) called “Dog Borstal” and it got me thinking…maybe a reality TV one-off or even a mini-series, called “Health Journo Borstal”? Like the dog version, we could be shown evidence of previous bad behaviour, then the miscreants undergoing retraining in boot-camp (by Ben G and the BTH team) and, in a nail-biting, will they, won’t they finale, having to pass a stiff test at the end by producing a good piece of health coverage.
    [/flight of fancy]

  9. jdc325 said,

    “Health Journo Borstal”
    Ahahaha – quality. Do you reckon we could make it compulsory? I keep imagining bemused hacks being told off for using relative risk figures now.

    PS – am unsure as to whether the flight of fancy relates to the mooted TV show or the idea that a health journo might produce a decent story. Frankly, the TV show seems less fantastical.

  10. Claire said,

    News media reporting of medical research features in Oct. 1 issue of JAMA, though the focus is on failure to report sources of bias when writing about medications, namely pharma funding. Medscape’s report of the article is free to access but requires registration – JAMA article needs a subscription.

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