September 08, 2023

6 min read

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Key takeaways:

  • Concentrations of surfactant protein-A were stable after exposure to candles.
  • Albumin increased after exposure to cooking and candles.
  • Lipid and lipoprotein concentrations increased with exposure.

Indoor air pollution caused by fumes from cooking and candles can cause irritation and inflammation as well as DNA damage in young individuals with mild asthma, according to a study published in Particle and Fibre Toxicology.

These findings suggest that patients with mild asthma should consider minimizing these exposures, Karin Rosenkilde Laursen, PhD, postdoctoral researcher in the department of public health at Aarhus University, and colleagues wrote.

candlelit dinner

A candlelit dinner and a home-cooked meal may seem cozy, but particulate pollution may impact any diners who have mild asthma. Image: Adobe Stock

“As we spend up to 90% of our time indoors, our health and well-being are affected by our indoor climate,” Laursen told Healio. “Growing evidence suggests that particle pollution is associated with a variety of adverse health effects ranging from inflammation to cardiopulmonary disease including cancer.”

Karin Rosenkilde Laursen

Cooking and candles emit high amounts of fine and ultrafine particles, she continued, which are small enough to penetrate the deepest regions of the lungs, translocate into the bloodstream and access vital organs such as the heart and brain.

“People with respiratory disease, eg, asthma, are known to be more susceptible to particulate air pollution than the background population due to chronic inflammation in the respiratory tract,” Laursen said.

Study design, results

The randomized, double-blind, controlled crossover exposure experiment comprised 36 individuals (20 females; mean age, 22.3 years) with mild asthma who did not smoke. They participated in three exposure sessions of 5 hours each, with each 2 weeks apart.

The first exposure involved air mixed with emissions from breast of pork cooked in forced air convection ovens with mean fine particle mass concentration of 96.1 µg/m3 (standard deviation [SD], 13.1).

During the second session, participants were exposed to air mixed with emissions from four taper candles and six pillar candles made of 100% stearin, with mean fine particle mass concentration of 89.8 µg/m3 (SD, 9.3).

The third exposure used clean filtered air with mean fine particle mass concentration of 5.8 µg/m3 (SD, 6.8).

Ranges of sums of 16 polycyclic aromatic hydrocarbons (PAHs) as defined by the EPA in these emissions included 0.16 ng/m3 to 1.3 ng/m3 (average, 1) for clean air, 0.88 ng/m3 to 1.6 ng/m3 (average, 1.1) for the cooking exposure and 7.8 ng/m3 to 21 ng/m3 (average, 10) for the candle exposure, indicating that cooking and candles are both sources of PAHs, the researchers said.

“We observed an increase in self-reported symptoms and discomfort when participants were exposed to emissions from candles and cooking, with cooking emissions resulting in several significantly increased symptoms such as eye irritation, nose irritation, headache, nausea, etc,” Laursen said.

“Females tended to report more severe symptoms than males throughout most questions. This is consistent with previous studies on the indoor environment,” she continued.

However, Laursen said that she and her colleagues were surprised that there was no change in lung function based on FEV1 after cooking and based on forced vital capacity after exposure to candles.

“Other studies examining nonasthmatics and asthmatics have found strong evidence for short-term effects of fine and ultrafine particles on lung function, especially in children,” Laursen said. “An explanation might be that the lung function measurements may be less sensitive to short exposures as seen in the current study, especially in young, relatively healthy individuals.”

Concentrations of surfactant protein-A (SP-A) in exhaled air remained approximately constant during the candle exposure. However, these concentrations tended to decrease 5 hours after the start of the clean air and cooking exposures.

SP-A concentrations were higher after candle exposure than after clean air exposure (0.31%; 95% CI, –0.02% to 0.63%), with varying significances across analyses, but there were no differences in SP-A after exposures to cooking and clean air.

Also compared with clean air exposure, nonsignificantly higher concentrations of albumin followed cooking (0.24%; 95% CI, –0.26% to 0.74%) and candle (0.25%; 95% CI, –0.25% to 0.75%) exposure.

Effect sizes for albumin/SP-A ratios included 0.08 (95% CI, –0.1 to 0.25) for cooking and –0.05 (95% CI, –0.22 to 0.13) for candles.

The researchers also called the decrease in IL-1 beta between 5 and 24 hours after cooking exposure significant (–0.2; 95% CI, –0.4 to –0.1), but they did not see any clear change in IL-1 beta after candle exposure (–0.09; 95% CI, –0.29 to 0.11), both compared with exposure to clean air.

There were significant or nearly significant decreases in IL-1 beta and TNF-alpha between 5 and 24 hours after cooking and candle exposure as well, compared with exposure to clean air, the researchers continued.

Additionally, the researchers called the 18.3 pg/ml (95% CI, 3.97-32.7) increase in CCL2 between 5 and 24 hours after candle exposure significant, compared with exposure to clean air. The difference between that increase and the 15.2 pg/ml (95% CI, 1.12-29.2) increase in CCL2 with cooking exposure also was significant, the researchers said.

Exposures to candles and cooking did not lead to any increase in C-reactive protein concentrations in plasma, nor was there any significant effect observed in early or late endothelial progenitor cells (EPCs), the researchers said.

But there were significant and borderline significant increases in early and late EPCs between 0 and 5 hours for all exposures, the researchers found, indicating diurnal effects, although there were no significant associations between exposures and EPCs in sensitivity analyses.

With the exception of a borderline significant positive regression coefficient of IL-8 after candle exposure of 0.39 (95% CI, –0.03 to 0.8), the researchers found no significant variations in the measured gene expression in peripheral blood mononuclear cells that were related to DNA repair or pro-inflammatory responses after cooking or candle exposure.

Although cooking and candle exposure did not have any significant effect on the level of DNA strand breaks either, the researchers said, there were elevated levels of sites sensitive to formamidopyrimidine DNA glycosylase after cooking exposure compared with exposure to clean air (regression coefficient on cube root scale, 0.06; 95% CI, 0.01-0.11).

Still, Laursen called the significant increases in oxidatively damaged DNA after cooking exposure particularly interesting.

“DNA damage is known to occur as a result of oxidative stress and inflammation,” Laursen said. “DNA damage is of concern, as replication of DNA may cause mutations possibly leading to cancer. Similar findings have been found in several studies of combustion particles.”

Nuclear magnetic resonance spectroscopy data indicated several significant peaks in metabolites and macromolecules, the researchers said, particularly with increasing concentrations of lipids and lipoproteins after cooking exposure compared with clean air exposure, although there were no significant associations between metabolites and candle exposure.

Conclusions, next steps

Based on these findings, the researchers concluded that cooking and candle burning can affect parts of the respiratory system, shifting some local and systemic biomarkers in young individuals who have asthma and indicating potential mild inflammation.

Differences in particle size and chemical composition may explain these different effects on health between cooking and candle burning, the researchers continued, adding that these findings warrant confirmation in future studies as well as the consideration of strategies to reduce indoor particle pollution to minimize disease progression.

“The results support recommendations to reduce indoor air pollution in order to protect the public, and especially people with respiratory disease, from potential adverse health effects,” Laursen said.

Doctors can be aware of the potential of cooking and candle exposure in reducing the well-being of their patients, such as worsening symptoms, and provide suggestions for what patients can do to improve their indoor climate, Laursen continued.

“Individual actions in private homes can reduce indoor particulate air pollution,” she said. “Cooking is for most people an inevitable part of everyday life. However, interventions to reduce air pollution caused by cooking can be established.”

Laursen noted that natural and mechanical ventilation are key in reducing indoor concentrations of particulate matter and recommended simple but effective strategies such as using a cooker hood and airing out the kitchen several times a day. Similar approaches can be taken with candles.

“Individuals can reduce the number of candles burned at once, but most importantly, they should remember to air out when candles are extinguished,” Laursen said. “One could recommend battery-operated candles instead of lit stearin candles.”

Laursen and her colleagues are continuing their work.

“We are currently a part of an innovation project called CANdle Development for Low Emissions with partners from several universities and industry, working on producing low-emission candles, with the aim of reducing indoor air pollution,” she said. “Furthermore, we would like to replicate the study on healthy individuals.”


For more information:

Karin Rosenkilde Laursen, PhD, can be reached at [email protected].

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