Painkillers and Parkinson’s

Regular use – two or more pills a week for at least a month – of over the counter painkillers “such as ibuprofen” can cut the risk of Parkinson’s disease by up to 60%, reported the Daily Mail . The “anti-inflammatory drugs could slow the onset of the disease by reducing the swelling of the brain”, said the newspaper.

The story is based on research in a group of 293 people, half of whom had Parkinson’s disease, using a questionnaire. The study found that people who used anti-inflammatory painkillers for over two years had a reduction in the risk of Parkinson's disease. However, people should be cautious about taking anti-inflammatory drugs on a regular basis, and should not increase or change their dose of painkillers, or start taking the drugs without discussing it with their doctor.

Where did the story come from?

Dr Angelika Wahner and colleagues from the UCLA School of Public Health conducted this research. The study was supported by a grant from the National Institute of Environmental Health Sciences and was published in the peer-reviewed medical journal: Neurology .

What kind of scientific study was this?

This was a case-control study, which compared the characteristics of 293 people with “possible or probable” Parkinson’s disease (PD) with 289 matched controls. All patients filled in a questionnaire that asked about their usage of non-steroidal anti-inflammatory drugs (NSAIDs); they were asked whether they had taken aspirin-based or non-aspirin-based NSAIDs (such as ibuprofen) once a week for at least a month at any point during their life. They were also asked how many pills they had taken each day or week, how long they had taken them for, and how old they were at first and last use.

From the responses to the questionnaires, the researchers then divided people into “regular users” or “non regular users” of aspirin or non-aspirin NSAIDs. They then used statistical tests to see which category people with Parkinson’s disease were more likely to fall into: ”regular” or “non regular” users. They then compared these numbers with the group without Parkinson’s disease. In this analysis, they controlled for gender, age at diagnosis, race, smoking, education, and county of origin.

What were the results of the study?

The study found there was no statistically significant difference in aspirin use between people with Parkinson’s disease and those without Parkinson’s disease. These results were adjusted for confounding factors that might have had an effect on the risk of disease.

For the group with Parkinson’s disease, the researchers found that regular use of non-aspirin NSAIDs (e.g. ibuprofen) was about 50% less common, suggesting that taking non-aspirin NSAIDs could protect against the disease.

When the researchers broke down the figures depending on how long people had been taking painkillers, they found that using them for more than two years meant a greater reduction in the risk of disease (56%). Analysing the data in this way showed that using painkillers for less than two years did not offer any protection at all.

When the figures were analysed by gender, they found that aspirin seemed to be more protective for women, but this result was still not statistically significant. Conversely, when they were analysed in this way, the non-aspirin NSAIDs seemed to offer real protection in women but not in men.

What interpretations did the researchers draw from these results?

The researchers conclude that their results add to the growing body of evidence that suggests NSAIDs protect against Parkinson’s disease. They call for further research to clarify and confirm these findings. In particular, they say that their research did not analyse the contribution of the different NSAIDs by type, that is, it only grouped them by “aspirin” and “non-aspirin NSAIDs”. They say that future studies should be designed to be able to tease apart the contributions of the different drugs.

What does the NHS Knowledge Service make of this study?

This is a fairly well-conducted study, but it suffers from some weaknesses as a result of its design, and there are several points to highlight:

People are unlikely to have remembered accurately exactly what medications they took and for how long over the course of their entire lifetime. People with Parkinson’s may also remember their lifetime drug use differently to people who do not have the disease. This will lead to imbalances and biases in the results.
The researchers performed quite a few subgroup analyses to analyse the information differently. There are inherent problems with this kind of “multiple testing”. There are obviously a smaller number of people in the groups being tested and this means that subgroups usually are not big enough for any real differences to be seen. Also, cutting up the data this way increases the chance of finding false positive results. The findings of the subgroup analyses should be interpreted with caution.
The “60% reduction in risk” figure reported by many of the newspapers appears to come from a subgroup analysis comparing people who took two to 14 pills per week and those who took more than 14 pills per week with those who were “non-regular users”. This showed that people with Parkinson’s disease were 64% less likely to have taken two to 14 pills per week at some point during their lifetime. This is a subgroup with a small number of people in it (only 67 out of the total 579 people were taking this “dosage”).
As the cases of Parkinson’s disease included in the study are considered to be “probable” or “possible”, this leads to the possibility of inaccuracies in the classification of those with and without the disease.
The causes of Parkinson’s disease remain largely unknown and may include genetic, environmental and other factors. There is currently no known way to prevent the development of the disease.
From the newspaper headlines, the public might gain the impression that taking regular anti-inflammatory drugs, such as over the counter ibuprofen, could reduce the risk of Parkinson’s disease. It is very important that the adverse health effects (including stomach irritation) and the risks to particular groups of patients associated with taking these drugs on a regular basis is highlighted.
People should not increase their dose of aspirin or other NSAIDs, or start taking the drugs, without first discussing it with their GP.

Sir Muir Gray adds...

Inflammation is different from infection; it is the body’s response to a number of different types of insult and injury, including infection. Some diseases cause an inflammatory response and anti-inflammatory drugs such as aspirin or NSAIDs can help not by tackling the disease itself, but by tackling the secondary inflammatory response.

This ‘may’ be the case with Parkinson’s disease but we need to see a systematic review of all the research on this topic before any recommendations can be made.