Monday September 17 2012
Ibuprofen and paracetamol are widely used to treat pain and reduce inflammation
The Daily Mail has reported that women who regularly take ibuprofen or paracetamol are 'more likely to lose their hearing'.
As millions of us take over-the-counter painkillers every year, the claim is an obvious concern, but is the science behind the story really worth listening to?
This story was based on a study that followed over 60,000 women for more than a decade and found that those reporting regular use of paracetamol or ibuprofen (defined as taking the drug two to three days per week, or more), were more at risk of reporting hearing loss in later life compared to those who took these painkillers less frequently.
For ibuprofen, the increase in risk ranged from 13% (when taken two to three days per week) to 24% (when taken on six or more days per week). The trend in paracetamol was less clear, but ranged from 8% to 21% increased risk, depending on the frequency at which the drug was taken. No link was found between the use of aspirin and hearing loss.
This large study suggests that women taking ibuprofen or paracetamol (but not aspirin) more than two to three days per week are more likely to report hearing loss in later life than those who don’t. However, the effects in other groups (such as men or children) are unclear, and the biological explanation for this reported link, are still unknown and require further research.
Taking the occasional pill when you have a sore head or a painful period probably isn’t going to pose a significant threat to your health. However, if you do find that you are using painkillers on a daily, or near daily, basis for long periods of time, seek advice from your GP.
Where did the story come from?
The study was carried out by researchers from Bingham and Women’s Hospital in Boston in the U.S. and was funded by grants from the U.S. National Institutes of Health and by funds from Vanderbilt University School of Medicine. No conflicts of interest were declared.
The study was published in the peer-reviewed American Journal of Epidemiology.
The Mail’s reporting was generally well balanced, including quotes from the study authors saying “they do not yet know why there is a link, or whether the damage caused is permanent” but the use of the term ‘deaf’ in the headline was unhelpful. For many people reading the article the term ‘deaf’ would imply significant or total hearing loss. In fact, women in the study reported only some degree of hearing loss and rated it as mild, moderate or severe. It is not clear from the study results what proportion of women, if any, had total hearing loss.
What kind of research was this?
This was a cohort study looking at the relationship between the use of ibuprofen, aspirin and paracetamol and self-reported hearing loss in female nurses during later follow-up.
This is an appropriate study design to investigate this potential link because the researchers will be able to establish whether the painkiller use preceded the hearing loss, providing a potential causal pathway. A cohort study involves gathering lots of information on health-related behaviours from participants (e.g. smoking habits, diet, physical activity levels, etc.) over the course of many years and recording what diseases and conditions they go on to develop. Researchers then review information collected in the past to find explanations for the illness.
What did the research involve?
The researchers examined the relationship between frequency of aspirin, ibuprofen, and acetaminophen (the U.S. name for paracetamol) use and risk of hearing loss among 62,261 women aged 31–48 years at the start of the study. The women were recruited in 1995 and followed up until 2009. These women were recruited as part of a larger cohort study called the Nurses’ Health Study II, which enrolled 116,430 female nurses in 1989.
In 1995 (and every two years after) the women were sent a questionnaire asking about their average use of painkillers, including aspirin, paracetamol and ibuprofen, and categorised their use as:
- once a week
- two to three times a week (further defined as “regular use” by the researchers)
- four to five times a week
- six or more times a week
In 2009 the women were sent a questionnaire asking “Do you have a hearing problem?” (with the response options, no, mild, moderate, or severe) and “If so, at what age did you first notice a change in your hearing?”. Cases of self-reported hearing loss were defined as those women reporting any hearing problem (mild, moderate, or severe). Women reporting tinnitus (persistent ringing or buzzing in the ears) were excluded. No objective or clinical measure of hearing loss was obtained.
The main analysis assessed the link between reporting hearing loss and use of aspirin, paracetamol and ibuprofen. The analysis took account of additional confounding factors (confounders) that were known to be associated with hearing loss and/or use of painkillers.
- body mass index (BMI)
- alcohol consumption
- intake of folate
- levels of vitamins A and B12, potassium and magnesium
- physical activity
- high blood pressure
- menopausal status
What were the basic results?
On first assessment (1995) 62% of women used paracetamol and 30% used aspirin at least once per week. Of the 77,956 women who returned the hearing questionnaire, 23.8% (nearly one in four) reported having a hearing problem.
Both ibuprofen and paracetamol use were independently associated with increased risk of hearing loss, but aspirin use was not.
Women regularly taking ibuprofen two to three days per week were 13% more likely to self-report hearing loss, compared to women taking it less than once per week (relative risk [RR] 1.13, 95% confidence interval [CI] 1.06 to 1.19). The relative risk of hearing loss rose with increasingly frequent use of ibuprofen. Those taking ibuprofen four to five days per week and more than six days per week were, respectively, 21% (RR 1.12, 95% CI 1.11 to 1.32) and 24% (RR1.24, 95%CI 1.14 to 1.35) more likely to self-report hearing loss compared to women taking it less than once a week.
For paracetamol, the increase in risk compared to women taking it less than once a week was 11% (RR 1.11, 95% CI 1.02 to 1.19) for two to three days per week, 21%(RR 1.21, 95% CI 1.07 to 1.37) for four to five days per week and 8% (RR 1.08 95% CI 0.95 to 1.22) for more than six days per week. The trend of increasing risk with increasing drug use was less clear for paracetamol than for ibuprofen.
Compared to no use, the authors found that regular use of all three painkillers increased the risk of self-reported hearing loss by 34% (RR 1.34 95% CI 1.15 to 1.56).
How did the researchers interpret the results?
The authors concluded that the use of ibuprofen and the use of paracetamol were “independently associated with an increased risk of hearing loss in women. The magnitude of the risk related to ibuprofen and acetaminophen [paracetamol] use tended to increase with increasing frequency of use. There was no relation observed between aspirin use and the risk of hearing loss.”
This large cohort study found that women who used paracetamol and ibuprofen more than two times a week were at slightly higher risk of reporting hearing loss years down the line compared to women who took the painkillers less frequently.
This study has many strengths, including its large size and prospective design. However, there are also important limitations, which could have influenced the results, that are outlined below.
One of the limitations of this study was that the women’s hearing loss was self-reported, rather than being assessed by a health professional or in another objective way. This self-reporting could have led to categorisation error, whereby those women defined as having hearing problems in the study may not have been found to have significant hearing loss if they were assessed professionally. Similarly, some of those that said their hearing was fine, may not realise that it wasn’t. In general, this could have altered the results, and a significant link between painkiller use and hearing loss may not have been found.
Despite its strengths, this study cannot prove causation, particularly as it is difficult to take into account all health factors that could possibly be associated with both painkiller use and later reports of hearing loss.
There could be a number of factors that cause some women to take painkillers on a frequent basis and it could actually be these factors that are responsible for the hearing loss. Not the painkillers themselves.
It is not clear from this study if the self-reported hearing loss was temporary or permanent. Similarly, it wasn’t clear how long women would have to regularly take paracetamol or ibuprofen for their risk of hearing loss to increase significantly. Likewise, it was not clear whether women who had regularly used painkillers in the past, and then stopped, had a normal risk level or whether it remained elevated. These are all questions that further research is likely to address.
A large proportion of the women (93%) self-identified as white and so the results may not necessarily be applicable to other ethnic groups.
As the study was only on female nurses, the results may not be directly applicable to men either. To counteract this the researchers highlighted previous research they had carried out which suggested that regular use (more than two times per week) of painkillers, including paracetamol and aspirin, was associated with an increased risk of self-reported and professionally diagnosed hearing loss in men. However, the authors state that they “cannot explain why we observed a positive association between aspirin use and risk of hearing loss in men but no relation in women.” This may, in part, be due to the fact that the biological method by which painkillers may cause hearing loss is not well understood. Therefore, further research is needed to elicit the key biological process linking the two, assuming such a link exists. Similarly, the effect of use in childhood, adolescence and young adulthood could not be assessed by this study.
This large study suggests that white women taking ibuprofen or paracetamol (but not aspirin) more than two to three days per week are more likely to report hearing loss in later life than those who don’t. However, the effect in men, different ethnicities, and the biological explanation for this reported link, are all still unknown.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.