It’s long been questioned whether the festive tradition of roasting giant pieces of meat causes a few undesirable health effects. But most of us probably hadn’t considered that some of these might be tied to breathing in what our ovens pump out.
In fact, as recent research from Denmark has highlighted, cooking (particularly roasting) and the burning of candles can damage your DNA. It's a study that adds to a large body of science examining the effects of indoor air pollution from a huge number of sources. So, what are the main contributors to poor air quality? And what can we do about them?
What are the main culprits when it comes to indoor air pollution?
According to indoor air pollution expert Prof Nicola Carslaw from the University of York, there are a lot of chemicals that could be a problem – a recent project she was involved in counted over 900 different substances of concern.
“Obviously, you can’t possibly think about 900 different chemicals in your average home,” she says. “So probably the most sensible way to do it is to think about sources.”
There’s a lot to consider: everything from painting and decorating products, kitchen and bathroom cleaners and beauty products like nail varnish can contain these chemicals.
Burning fuels in hearths or on stoves, as well as candles, produce one of the main types of pollutants, particulate matter – a mixture of dirt, soot and different chemicals all stuck together.
Then there are volatile organic chemicals (VOCs). These are a large group of airborne chemicals that can be released by building materials and new furniture, but equally from cooking and consumer products. And of course, outdoor pollution can also creep indoors.
What does cooking contribute to the mix?
Cooking generates a lot of particle emissions, which come, as in a car engine, from burning fuels – like when you use a gas hob – but also from frying meat in oil, for instance. In less developed countries, the widespread use of fuels like kerosene (paraffin) and coal for cooking takes a massive toll on people’s health.
The World Health Organisation estimates that three million people die prematurely each year due to cooking emissions that increase their risk of diseases including heart disease, stroke and lung cancer.
“It’s a very different problem in some countries,” says Carslaw. “And it's probably more to do with the fuel that they're burning rather than the cooking per se.”
By comparison, people living in European countries cook in a relatively clean way, but are still exposed to emissions from the heating and cooking of the food itself. However, due to limited research, it’s very difficult to understand how harmful these emissions are compared to, say, traffic emissions.
Is it safe to roast a turkey or light a candle this Christmas?
We shouldn’t worry too much about having one big cook-out, or lighting a candle occasionally. But the recent study, led by Karin Rosenkilde Laursen at Aarhus University in Denmark, does offer new insights into how cooking and candles, specifically, might influence our health.
She and her co-workers asked people with mild asthma to sit in a closed chamber for five hours, in clean, filtered air, or whilst emissions were funnelled in from a connecting chamber where either pork was roasting in an oven, or several candles were burning.
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Their results show that cooking and burning candles produced different sizes of particles and types of chemicals, which may influence their precise effects, but that both sources raised levels of proteins associated with inflammation of the airways. For cooking particularly, Laursen also notes effects on DNA.
“We saw that when exposed to cooking emissions, people actually had DNA damage,” she says, explaining that DNA damage can be associated with cell repair processes that trigger cancer-causing mutations.
“So, it is not that we observed cancer or even cancer pre-stages, but we observed this DNA damage, which may at some point, in the long run, lead to mutations that lead to cancer.”
When participants sat in the clean, filtered air, some of their inflammation markers actually went down, suggesting that many of us are faced with such a constant bombardment of chemicals that our levels are always slightly raised.
What can we do to reduce indoor air pollution and its health effects?
Carslaw’s approach is “ventilation, moderation, education”. By ventilation, she means opening windows and using cooker hoods that extract and eject the harmful emissions (noting that some vent them back into the kitchen).
Moderation is about considering how often we use, for example, scented candles, or harsh cleaning products like bleach. First, though, comes education, as while the harmful effects of air pollution are well-recognised for the outdoor environment, it’s not the case indoors.
As far as cooking emissions are concerned, no one is suggesting switching to takeaways, but we could modify how we cook and deal with the emissions. For example, cooking meat at high temperatures with lots of fat produces more harmful emissions than boiling pasta.
As Laursen points out, though, “You should also eat varied foods, so I keep on cooking all the foods, but I just use my cooker hood every time and then air out afterwards," she says.
With Christmas just around the corner, she also offers a final tip for those who like to burn an advent candle: a flickering flame indicates increased particle production, so place it where it burns steady and does not waver.
About our experts
Prof Nicola Carslaw is a researcher in environment and geography based at the University of York. She specialises in modelling the chemistry of air pollution in indoor environments. Her work has been published in the journals Environmental Sciences: Processes & Impacts, EGUsphere and Indoor Air.
Karin Rosenkilde Laursen is a post-doctoral researcher at the Department of Public Health - Institute of Environmental and Occupational Medicine at Arrhus University. Her work has been published in the journals Indoor Air and European Clinical Respiratory Journal.
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