In this study, we conducted an ecological analysis of data from 73 countries to examine the relationship between energy-related methane emissions and the burden of CVD in 2019. Our results indicate that methane emissions are significantly associated with the burden of CVD in the analyzed nations. Specifically, we found a positive correlation between methane emissions and the total DALYs attributed to CVD, indicating that higher methane emissions are associated with a greater burden of CVD. These results are in line with previous research linking air pollution and cardiovascular disease22,23,24,25.
It is worth noting the methodological limitations of ecological studies when interpreting the results. Our analysis is based on country-level data, which may not accurately reflect the individual-level exposure and health outcomes. Other factors not accounted for in our study, such as lifestyle and genetic factors, could also contribute to the development of CVD26.
In the energy industry, methane emissions are primarily generated through the extraction, production, and distribution of natural gas, which is composed mainly of methane. Methane is released into the atmosphere during the drilling, completion, and production of natural gas wells, as well as during the processing, storage, and transportation of natural gas27.
During the drilling process, methane can escape through leaks in the well casing or from venting and flaring of natural gas28. Methane can also be released during hydraulic fracturing, or fracking, when high-pressure fluids are injected into shale rock to release trapped natural gas29. Methane emissions can also occur during the processing and transportation of natural gas through pipelines, compressors, and other equipment30.
Additionally, methane can be released during coal mining operations when methane is trapped in coal seams and is released as the coal is mined31. Methane emissions can also occur during oil production when methane is co-produced with oil and is released through venting or flaring32.
The IEA, from where our data were obtained, reports a wide range of energy-related methane emissions registered across countries. This high variability could be attributed to differences in energy production and consumption patterns, as well as differences in the regulation and implementation of emission reduction policies33. For instance, Indonesia reported the highest methane emissions, which could be attributed to its large coal and oil industries, while Guinea reported the lowest emissions, which could be due to its low levels of industrialization.
Methane can enter the body through inhalation or ingestion34. Inhalation of methane can occur through breathing contaminated air, such as in occupational settings where workers are exposed to high levels of methane, or in areas with high levels of methane emissions, such as landfills or natural gas extraction sites35. Once inhaled, methane can be absorbed into the bloodstream through the lungs, where it can then be transported to other organs in the body.
Ingestion of methane can occur through the consumption of contaminated food or water36,37. Methane can be produced in the digestive system of certain animals, such as cows and sheep, and can be released into the environment through their excrement38. Contaminated food or water can contain high levels of methane, which can then be ingested and absorbed into the bloodstream through the digestive system.
Several mechanisms may be involved in the pathogenesis of CVD that are influenced by exposure to methane gas. Methane exposure has been shown to increase oxidative stress39, inflammation, and vascular dysfunction40, all of which are key risk factors for CVD.
Within the cells, methane can interact with mitochondria and may disrupt their function and compromise the electron transport chain, leading to the leakage of electrons and the generation of reactive oxygen species (ROS)16. The accumulation of ROS can overwhelm the endogenous antioxidant defense system, comprising enzymes such as superoxide dismutase, catalase, and glutathione peroxidase41. As a result, the balance between ROS production and antioxidant capacity is disrupted.
Oxidative stress and inflammation are closely interconnected processes that play critical roles in human health and disease42. Inflammation seems to be a key risk factor for cardiovascular diseases, as chronic inflammation can lead to the development of atherosclerosis43,44. Methane exposure has been shown to increase the production of pro-inflammatory cytokines and other markers of inflammation in the cardiovascular system, which can contribute to the development of atherosclerosis and other cardiovascular diseases45.
To the best of our knowledge, there are no published data estimating the attributable risk of methane emissions on CVD-related burden of disease. However, a recent and interesting publication considered that 2 out of 10 deaths due to non-communicable diseases may be attributed to ambient air pollution46. The CVDs that may arise, at least in part, from exposure to environmental methane emissions and other air pollutants include coronary heart disease, stroke, and heart failure7.
In our study, we observed significant variation in the burden of CVD across nations, with some countries reporting much higher DALY counts compared to others. This variation could be attributed to differences in CVD risk factors, including hypertension47, smoking48,49, and physical inactivity50, as well as differences in healthcare infrastructure and access to healthcare services51,52. This highlights the importance of understanding the unique socio-economic and environmental factors that may contribute to CVD burden in different regions.
We used age-standardized prevalence of obesity as an adjustment variable, given its established link to CVD53. However, we observed a significant but inverse relationship in the 73 countries analyzed.
Life expectancy at birth (measured in years) was included as a potential confounding variable in our study. It was chosen as a proxy for a range of unobserved characteristics present within a population. Life expectancy at birth is known to be influenced by various factors, such as healthcare access, socioeconomic conditions, environmental quality, and lifestyle behaviors, among others54,55. These factors may have indeterminate effects on the outcome of interest in our research.
However, we acknowledge that including obesity prevalence and life expectancy does not eliminate all potential confounding factors in a study of our nature. Therefore, we emphasize that the limitations associated with an ecological approach must be carefully considered when interpreting the findings presented.