“The natural gas industry has a long history of safely delivering energy to customers and communities across the nation, and we are focused on bringing sound science to any discussion around the role of natural gas in our nation’s energy future,” said AGA President and CEO Karen Harbert. “With that in mind, we have embarked on an effort to work with experts in the fields of epidemiology and toxicology to contribute objective, thorough and meticulous science to the policy discussions around the health impacts of natural gas stoves. This study comprehensively demonstrates that prior studies on natural gas cooking and NO2 and asthma and wheeze are highly variable and have quality flaws, and as a consequence, there is no scientific basis to draw any conclusions concerning a causal relationship.” 

This systematic review looks at literature on the associations between gas stoves and indoor NO2 and asthma and wheeze in children and conducts an in-depth evaluation of study heterogeneity and study quality, neither of which has been done previously. A protocol was filed before the review began that set out the methods and criteria that would be used. In total, the authors identified and reviewed 66 studies (41 included in a prior meta-analysis by Lin et al., 5 published before 2013 but not included in Lin et al., and 20 subsequent).  

The comprehensive review finds that studies generally have high variability in terms of study region, age of children, exposure definition and outcome definition. Studies also generally have low quality: “a large proportion of the studies to date are subject to multiple sources of bias and inaccuracy, primarily due to self-reported gas cooking exposure or respiratory outcome, insufficient adjustments for key confounders (e.g., environmental tobacco smoke, family history of asthma or allergies, socioeconomic status or home environment) and unestablished temporality.”  

Most of the studies, especially the studies of natural gas cooking, were cross-sectional in design, meaning they are observational in nature and cannot establish causation. Cross-sectional studies are favored for initial research because they are inexpensive and easy to perform, but they cannot be used for causal inference because they do not assess whether exposures occurred before the health outcomes. Only a few of the natural gas cooking studies were cohort studies, meaning they followed subjects over time, and those studies largely reported null findings; while more indoor NO2 studies were cohort studies, temporality was only established in a few, and those studies largely reported null findings as well. The authors conclude that “the epidemiology literature is limited by high heterogeneity and low study quality and, therefore, it does not provide sufficient evidence regarding causal relationships between gas cooking or indoor NO2 and asthma or wheeze.” 

Some more recent studies and reports have ignored the limitations of the epidemiology literature, and instead begin from a biased assumption that a causal relationship between gas cooking and asthma has been demonstrated in the prior Lin et al. meta-analysis, and then proceeded to extrapolate from there without consideration of the underlying studies. This is especially problematic because the results of these varied and potentially unreliable studies cannot be combined to come up with reliable statistical risk estimates. 

Harbert continued, “Consumers deserve transparent information about the energy they use, and policymakers need good science to make informed decisions. Unfortunately, many headline-grabbing studies we have seen around natural gas are focused on a predetermined outcome rather than a transparent and deliberative scientific process. As concerns over emissions from gas ranges are raised and debated, the natural gas utility industry is focused on bringing objective technical information to the discussion. We will continue to work to ensure regulators and policymakers can confidently make decisions based on sound data developed using reliable methods as they approach any issues related to natural gas.”