Study Links Fireplaces to Cognitive Decline

Indoor particulate pollution from burning wood or peat is similar to standing by the side of a road.

Wood fire at Shoe Lake

Lloyd Alter

There's nothing like a roaring fire on a cool evening. The one in the photo is in my cabin in the woods, near Algonquin Park in Ontario, Canada; it is our primary source of heat for a few days in spring and fall. I designed this before I knew what a bad idea it was due to the tiny particulate matter (PM2.5) it is pumping out.

Now a new study, "Indoor Particulate Air Pollution From Open Fires and The Cognitive Function of Older People," finds that it is worse than we thought. Researchers led by Barbara Maher of Lancaster University studied the association between the usage of open fires and cognitive function. The authors write:

"We found a negative association between open fire usage and cognitive function as measured by widely-used cognitive tests such as word recall and verbal fluency tests. The negative association was largest and statistically strongest among women, a finding explained by the greater exposure of women to open fires in the home because they spent more time at home than men."

Treehugger has noted before that living near a highway could increase your dementia risk, and the new research essentially concludes that having an open fire is comparable to living near a highway. The study compared the estimate of open fire usage of five hours per day for six months and compared it to previous studies looking at the exposure from urban commuting one hour a day for 12 months.

The researchers note that most studies linking PM2.5 focused on the outdoor environment, but most people spend the majority of their time indoors, not out. Like the particulates that come from car exhaust and tire and brake wear outside, the PM2.5 released by burning wood inside contains a lot of magnetic, iron-rich ultra-fine particles (UFP) which have been found in human brains and are directly associated with Alzheimer's Disease. The study measured the concentrations of magnetic content in airborne PM from open fires and "examined the association between cognitive function and open fire usage among older people living in Ireland."

Why Ireland? There is a significant proportion of people who burn wood, coal, or peat in open fires as their primary source of heat. As recently as 1981, 70% of households did it; today it is still about 10%.

The researchers conclude that burning solid fuel in a fireplace creates levels of PM that are similar to and might even exceed those by the side of a busy road, and that the particles might also include not only magnetite but other metals that are linked with cognitive function. They write:

"Our analysis shows that the dose of inhaled PM2.5 from open fires might exceed that at the roadside. A person staying at home and using an open fire to keep their home warm might thus be exposed not only to high concentrations of magnetite, but also to other neurotoxicants contained within PM2.5."

The researchers found levels of PM2.5 of 60 μg/m3 from burning peat, 30 μg/m3 from burning coal, and 17 μg/m3 from burning wood. These are all higher than the 10 μg/m3 that was recently recommended by an independent panel in the United States. But most researchers suggest that there is no minimum.

They conclude that "a negative association has been found between open fire usage and cognitive function."

But What About Occasional Use?

A friends fireplace
Lloyd Alter/ a friend's lovely fireplace

The Guardian had a surprisingly humorous take on the study, warning about chestnuts roasting on an open fire being a bad idea this Christmas. But the study was looking at the long-term use of open fires as a source of heating for five hours a day half the year, not as a source of what might be called decorative or recreational fires. Are the study results actually relevant to this? Study author Barbara Maher told Treehugger:

"‘Recreational’ use of open fires, as you describe it, would result in much less exposure….but it doesn’t look like there’s any ‘safe’ level of exposure, and the more people who burn fuel for domestic heating (even infrequently), the more that outdoor PM levels increase too, often in cold, high-pressure conditions, with little wind to disperse the emissions. It’s also likely that an individual’s response to exposure to particulate air pollution will vary depending on their resilience or vulnerability (i.e. the body’s genetically-controlled ability to deal with the particles and any associated inflammatory responses, together with any pre-existing conditions, eg heart or lung disease etc)."

We have discussed this many times on Treehugger before, and this study just adds more evidence, more fuel to the fire. As I wrote previously, "as the dangers of PM2.5 become more clear, it is becoming also clear that as charming and beautiful as fireplaces and wood stoves are, we should not be burning wood at all."

Meanwhile, Also On Treehugger:

leaves on tree
CC BY-SA 2.0. Wikimedia

Professor Maher noted that Treehugger had previously covered her work: "I think you’ve written before about our studies using roadside trees both to monitor particulate air pollution and to ‘capture’ it." Indeed we did; my colleague Michael Graham Richard wrote Trees Are Awesome: Study Shows Tree Leaves Can Capture 50%+ of Particulate Matter Pollution.

View Article Sources
  1. Maher, Barbara A. et al. "Indoor Particulate Air Pollution From Open Fires And The Cognitive Function Of Older People". Environmental Research, vol 192, 2020, pp. 110-298. Elsevier BV, doi:10.1016/j.envres.2020.110298.

  2. "The Need For A Tighter Particulate-Matter Air-Quality Standard". Vol 383, no. 7, 2020, pp. 680-683. Massachusetts Medical Society, doi:10.1056/nejmsb2011009.