More than a century of burning fossil fuels and other activities have increased the atmospheric concentration of methane and carbon dioxide, so-called greenhouse gases, that trap heat. Increased concentrations of these greenhouse gases have resulted in global warming, an important factor in climate change, causing shifts in weather patterns, rising sea levels and the disturbance of ecosystems.

Climate change can also affect our health, particularly our hearts.

Global warming stands to undermine the progress made in the prevention and treatment of cardiovascular disease (CVD) over the last 20 years, according to an analysis by researchers from Harvard and Beth Israel Deaconess Medical Center in Boston.

People who have to work outdoors, such as agricultural workers, and older people with heart conditions are likely to have an increased risk of another heart attack or stroke.

The researchers found that extreme temperatures and weather events such as hurricanes were associated with increased rates of morbidity and mortality from CVD. Older adults, minority populations and people living in disadvantaged communities were the most affected.

“Climate change will affect us all, but it will not affect us all equally,” Dhruv Kazi, corresponding author on the study, told TheDoctor. The effects of climate change are primarily a function of exposure and risk. People who have to work outdoors, such as agricultural workers, may be at increased risk of cardiac events. Older patients and those who have heart conditions may have an increased risk of another heart attack or stroke. Data from almost 500 observational studies were included in the current analysis.

Climate change affects cardiovascular health through four routes, they found:

  • Direct physiological changes in the body. Being exposed to extreme heat raises one's heart rate and blood pressure. Ozone or wildfire smoke gets into the lungs and can trigger systemic inflammation.
  • Negative effects on mental health. Heat and wildfires can cause acute stress and anxiety and, over the short-term, can worsen depression. Stress, anxiety and depression have been shown to increase the risk of CVD.
  • Disruptions or damage to the healthcare infrastructure. Flooding or power outages may close healthcare facilities. People may be unable to access medication, some of which may require refrigeration, or healthcare services.
  • Long-term socioeconomic effects. Changes in rainfall patterns and increasing temperatures may result in decreased agricultural productivity in some parts of the world. The resulting food insecurity may negatively affect nutrition and cardiovascular health. Migration associated with climate change may affect how people seek cardiovascular care and where it is available.

The long-term socioeconomic effects of climate change are as yet unknown, and more work is needed. Very little data exist from low-income countries in Asia and Africa, Kazi, the associate director of the Richard A. and Susan F. Smith Center for Outcomes Research in Cardiology at Beth Israel Deaconess Medical Center, explained.

“This paper was as important to us for what we did find as for what we didn't find,” he said. Going forward, he and the team are particularly interested in understanding the effect of environmental exposures due to climate change on pregnant women. Larger data sets in the U.S. are needed to study geographical differences in the effects of climate change.

The study was published in JAMA Cardiology.