Do Gas Appliances Impact Asthma?

Gas appliances – kitchen stoves, clothes dryers, furnaces for home heating, fireplaces, space heaters or water heaters – use natural gas as their primary source of heat. In fact, almost half of American households have gas stoves in their kitchens which they use daily. Both the stoves, and other gas appliances, produce respirable irritants that accumulate in indoor air, especially in winter months. Those irritants are a by-product of combustion and include nitrogen dioxide (NO2), carbon monoxide (CO) and particulate matter (PM).

Gas kitchen stoves are a primary concern, because they release irritants directly into the kitchen. Other appliances are less worrisome since they are located in areas with lower human traffic levels. Depending on the age and type of gas stove, the level of emissions will vary. Older stoves with a continuously-burning pilot light produce significantly more irritants than stoves with electronic ignition systems.

The use of stoves as a heat source is a hallmark of urban poverty. When stoves are used to heat a house, irritants spread throughout the living area.

Gender related effects

A cross-sectional study in East Anglia found gas cooking was positively associated with asthma symptoms such as wheeze and shortness of breath; with exacerbations; and with use of asthma medications. Women who used a gas stove or had an open gas fire showed reduced FEV1 and increased airway obstruction as compared with women who used non-gas appliances for cooking. The risk of symptoms associated with gas cooking was increased (though not significantly) in atopic women. Further, women who were exposed to gas stoves had lower lung function than men. The authors of the study hypothesized that the results could be explained by the fact that women spend more time cooking than men and short, intense exposures may be more harmful than brief exposures over a long period of time.(1)  

In yet another comparison, this time against homes with electric stoves, girls with asthma living in homes where cooking was done with gas stoves, and who did not use prescription medication for their asthma, had consistently lower lung function.(2)

Effects on children

Researchers in Victoria, Australia interviewed parents of 148 children, of whom 53 had asthma.(3) Nitrogen dioxide (NO2) levels in their homes were measured. Gas stove exposure was associated with a diagnosis of asthma (OR 2.23) and pulmonary symptoms (OR 2.32). Even after adjusting for NO2 concentrations, the association of gas stoves and respiratory symptoms remained significant (OR 2.24).

Another study involved 728 children under the age of 12 years with active asthma. NO2 levels were measured and recorded in the presence of gas appliances in their homes. Data were analyzed by by type of housing, and adjusted for confounders such as socioeconomic status.(4) When children with asthma in single-family housing were compared with children with asthma in multi-family housing who were exposed to gas stoves, but not gas dryers, the latter had increased symptoms of:

  • shortness of breath (OR 2.38)
  • wheeze (OR 2.27)
  • chest tightness (OR 4.34)

Further, children in multi-family housing were exposed to higher concentrations of NO2 than children in single-family homes, while those exposed to more than 20ppb of NO2 in the home had increased days of wheeze and chest tightness.

Inner-city children tend to spend more time indoors, and hence have greater exposure to indoor air pollutants. An inner city study(5) of 150 pre-school children, mostly African-American from low-income families, found that while concentrations of NO2 and particulate matter (PM) did not differ between cases and controls, children were often exposed to high NO2 concentrations. Gas stoves were the largest contributor to NO2 concentrations. The study found the non-atopic children who were exposed to levels higher than the 75 percentile of NO2 were at: 

  • increased risk for > 4 days of symptoms in a two-week period (OR 1.75)
  • decreased peak flow (< 80% expected) in the winter months (OR 1.46)

Inadequate ventilation and high levels of NO2 aggravate asthma symptoms. Every 20 point increase in NO2 concentration lead to a:

  • 10% increase in the number of days of coughing and nocturnal symptoms
  • 15% increase in the number of days of limited speech due to wheezing

Gas stoves and the use of a gas space heater or oven/stove for heating were significantly associated with high nitrogen dioxide levels and NO2 levels were significantly associated with asthma symptoms.

A recent study(6) of 7,300 children, aged 2 to 16 and with asthma, bronchitis or wheezing found that ventilation made a difference when gas stoves were used for cooking and/or heating. When used for cooking alone, compared with homes without ventilation, the incidence for:

  • asthma was 32% less
  • bronchitis was 38% less, and
  • wheezing was 39% less.

When gas stoves were used for heating in properly ventilated homes, the incidence of asthma was 49% less, and for bronchitis, 43% less, than in homes with poor or no ventilation.

Nitrogen dioxide and ETS

Both NO2 and ETS have been associated with adverse pulmonary effects. Kattan and colleagues looked at the effect of NO2 combined with environmental tobacco smoke (ETS) in children.(7) They collected data on children between the ages of 4 and 9 years who had asthma. The study population, mostly African-American and Hispanic, had high-level social and psychological stress, allergen skin test reactivity and exposure to both NO2 and ETS. ETS exposure was measured through cotinine levels and higher values were found in cooler weather, in girls and in homes where the caregiver had not completed high school (Relative risk 1.21). NO2 levels varied only by site. Of the 469 homes, 87.8% used gas stoves. The median level of NO2 was 29.9 ppb from a range of 0.5 to 480.1 ppb. The researchers concluded that higher levels of indoor NO2 are associated with increased asthma symptoms in non-atopic children (Relative risk 1.75) and that it lowered peak flows during colder months (Relative risk 1.46).

Asthma and gas appliances

Belanger and Triche examined recent literature discussing exposure to indoor combustion and asthma development and severity.(8) They concluded that there was some evidence for a link between exposure and asthma, “particularly asthma symptoms in children”. Another study, this time in Tasmania, of children of 863 parents involved in an asthma study, showered that children exposed in infancy to gas heaters were more likely to develop asthma and have recent wheeze by age 7.(9) (Data were adjusted for both gas cookers and smoking in the home.) Data regarding residential exposures and asthma from the National Health and Nutrition Examination Survery III were obtained from parents of a cross-section of a representative sample of over 8,000 US children under the age of 6. Children in homes where gas cookers were also used for heating had an increased risk (OR 1.8) of physician-diagnosed asthma.(10)

Conclusion

Since children spend most of their time indoors, exposure to NO2 should be a cause for concern. There appears to be a dose-response relationship between NO2 and asthma symptoms, and early exposure to gas stove emissions may cause nasal and lower respiratory tract symptoms. The risk appears to be greater for atopic children and adults. Thus questions as to the type of heating and cooking used and ventilation, together with interventions to reduce NO2 exposure, may help reduce asthma morbidity and improve the quality of life, particularly for children.

Abbreviations:

ppb: parts per billion
ETS: environmental tobacco smoke
FEV1: forced expiratory volume in one second
NO2: nitrogen dioxide
OR: odds ratio

References:

  1. Jarvis D, Chinn S, Luczynska C, Burney P. Association of respiratory symptoms and lung function in young adults with use of domestic gas appliances. Lancet. 1996;347(8999):426-31.
  2. Chapman RS, Hadden WC, Perlin SA. Influences of asthma and household environment on lung function in children and adolescents: the third national health and nutrition examination survey. Am J Epidemiol. 2003;158(2):175-89
  3. Garrett MH, Hooper MA, Hooper BM, Abramson MJ. Respiratory symptoms in children and indoor exposure to nitrogen dioxide and gas stoves. Am J Respir Crit Care Med. 1998;158(3):891-5.
  4. Belanger K, Gent JF, Triche EW, et al. Association of indoor nitrogen dioxide exposure with respiratory symptoms in children with asthma. Am J Respir Crit Care Med. 2006;173(3):297-303.
  5. Hansel NN, Breysse PN et al. A longitudinal study of indoor nitrogen dioxide levels and respiratory symptoms in inner-city children with asthma. Environ Health Perspect 2008; 116(10):1428-32
  6. Kile ML, Coker ES, Smit E et al. A cross-sectional study of the association between ventilation of gas stoves and chronic respiratory illness in U.S. children enrolled in NHANES III. Environmental Health, 2014; 13 (1): 71 DOI: 10.1186/1476-069X-13-71
  7. Kattan M, Gergen PJ, Eggleston P, et al. Health effects of indoor nitrogen dioxide and passive smoking on urban asthmatic children. J Allergy Clin Immunol. 2007;120(3):618-24. 
  8. Belanger K, Triche EW. Indoor combustion and asthma. Immunol Allergy Clin North Am. 2008;28(3): 507-19, vii.
  9. Ponsonby AL, Couper D, Dwyer T, et al. The relation between infant indoor environment and subsequent asthma. Epidemiology. 2000;11(2):128–35. 
  10. Lanphear BP, Aligne CA, Auinger P, et al. Residential exposures associated with asthma in US children. Pediatrics. 2001;107(3):505–11.