Last year, researchers said they had identified a link between wildfire smoke and increased risk of dementia.
Now, they’re retracting the study, published last November in the journal JAMA Neurology, after discovering a mistake in how they coded the data.
“It was a very small error. We had a single ‘or’ symbol, where we should have had an ‘and’ symbol in thousands of lines of code,” said Joan Casey, one of the co-authors of the study.
They’ve corrected the error, crunched the data again and republished their paper. Now, the authors say their findings suggest a much more subtle link between wildfire smoke and dementia.
“We now have a nuanced finding in the corrected result,” said Casey, who is a professor in the school of public health at the University of Washington.
Initially, Casey and her colleagues had found when the three-year average concentration of wildfire PM2.5 (the average concentration of fine particulate matter in the air due to wildfires in the region) went up by just one microgram per cubic metre of air, there was an associated 18 per cent of increase in the odds of a dementia diagnosis.
Now, Casey believes the increase to be closer to 12 per cent.
The finding is also no longer statistically significant, meaning there is some possibility the result is due to chance.
But that doesn’t mean the researchers were wrong to identify the possible link, says Scott Weichenthal, a professor in the department of epidemiology, biostatistics and occupational health at McGill University. It just means the link needs to be studied further.
“The data still suggests there’s a positive association there for sure. It’s just not quite as strong as it was in their original paper,” said Weichenthal, who was not involved with the study.
A growing body of research already links long-term exposure to air pollution with an increased risk of dementia. What’s less established, is whether specific sources of air pollution — like wildfire smoke — affect the risk of dementia.
There’s been a limited number of studies, like this one, suggesting wildfire smoke from agriculture and wildfires were associated with higher rates of dementia.
Weichenthal says researchers have a long way to go in understanding the long-term effects of wildfire smoke, especially on peoples’ brains.
“It’s not as developed as the databases for heart and lung effects,” he said.