Introduction
Greenhouse gases are at their highest levels in 2 million years. As a result, the earth is now 1.1 degrees Celsius warmer than it was in the late 1800s. The effects of these changes are becoming evident across the globe resulting in droughts, water scarcity, extreme weather events, severe fires, rising sea levels, and declining biodiversity. It is likely that land temperatures in Africa will rise faster than the global average, especially in more arid regions, with projections indicating that extensive areas of Africa will exceed 2°C by the last 2 decades of this century, relative to the late 20th century mean annual temperature. (1,2) Africa will be one of the regions most impacted by the adverse effects of climate change because of high exposure to environmental change, high dependence on agriculture for livelihood and limitations to adapt to these changes. (1)
Climate change and climate variability thereof have the potential to exacerbate or multiply existing threats to human security including food, health, and economic insecurity, all being of particular concern for Africa. In South Africa, climate change is leading to increases in temperatures and rainfall variability, which will amplify existing stress on water resources, vulnerable ecosystems and agriculture. (3) These increasing temperatures, changing rain patterns and increased evaporation led to a major drought in the Western Cape in 2017, (4) and, more recently, above average precipitation in April 2022 resulted in devastating floods in the coastal province of Kwazulu-Natal. (5) In this review we discuss the environmental exposures as a consequence of climate change and the relationship of these exposures on cardiovascular health; and discuss mitigation and adaptation strategies to counter the cardiovascular effects of climate change.
Effects of Climate change on Cardiovascular Health
The effect of climate change on cardiovascular health has a global impact especially in people with pre-existing medical conditions such as cardiovascular disease (CVD), patients with type 2 diabetes mellitus, hypertension as well as vulnerable populations, particularly the elderly. Adverse weather patteern changes are likely to have both direct and indirect adverse effects on CVD and on the care of such patients. (6) Exposure to extreme weather events, heat waves, cold spells and pollutants are examples of direct effects, which can contribute to the development of CVD but also exacerbate disease in individuals with CVD. (Figure 1) Indirect effects of climate change on CVD are more complex and relate to lack of water and food security, vulnerable populations, migration, and overburdened healthcare systems. (7)
Extreme weather
The recent extreme heatwaves and wildfires in the UK and Western Europe are prime examples of extreme weather due to climate change. (8) Climate change is intensifying these heatwaves as increased greenhouse gas raises temperatures and dries out the soil. (9) Heat-related health effects may also be of concern in Southern Africa, (10) since Africa is currently experiencing significant heat stress based on the nature of the continent and the current environmental crisis. (11)
Although it is expected that extreme weather changes would be associated with increased risk of stroke and myocardial infarction, (12) definite causal links between rising temperatures or heat waves and adverse cardiovascular events are inconsistent. German data has suggested a relationship between rising temperatures and myocardial infarction especially among patients with predisposing risk factors. (13) However, data from Spain and the UK did not find an association between warmer temperatures and myocardial infarction and studies showing a relationship between changes in ambient temperature and atrial fibrillation or heart failure are lacking. (6,14) In contrast to gradual increases in ambient temperature, heat waves, which are defined differently in various studies, have been associated with increased admissions among patients with underlying cardiovascular diseases. (15) However, studies linking heatwaves to myocardial infarction, heart failure or arrhythmias are scarce.
Despite the lack of a clear link between changes in ambient temperature and heatwaves and CVD, several mechanisms have been proposed whereby rising temperatures could lead to an increase in adverse cardiovascular events. (6) An elevated body core might result in dehydration, increased blood viscosity and sympathetic nervous system activation. (16) Haemoconcentration contributes to a hypercoagulable state, which may increase the risk of thrombosis. Together with a heightened sympathetic state, vulnerable patients are likely to be at increased risk of plaque rupture and thrombus formation. (17)
Similarly, cold spells have been associated with an increased incidence of myocardial infarction. (6) Cold can increase sympathetic nervous system activation, leading to a rise in catecholamine levels, vasoconstriction, increased heart rate and blood pressure. An increased blood pressure decreases the ratio of myocardial oxygen supply to demand and may lead to myocardial ischemia, particularly in a vulnerable myocardium and thereby increasing the risk of myocardial infarction. Furthermore, a drop in core body temperature can lead to cholesterol crystallization in atherosclerotic plaques, increasing the risk for plaque rupture. (18)
Air pollution
Air pollution, arising from fossil fuel burning and wildfires, is a major contributor to climate change. These pollutants include carbon monoxide, sulphur dioxide, nitrogen oxides and particulate matter (PM), levels of which are exacerbated by the “climate penalty” of climate change (causing meteorological disruptions, which leads to increased PM in the atmosphere). The recently published Global Health Data Exchange suggests that air pollution is responsible for an estimated one-fifth of global deaths from cardiovascular disease. (19) Multiple studies have demonstrated that air pollution has adverse effects on CV morbidity and mortality. It is likely that South Africans are at increased risk for PM exposure because South Africa continues to rely on coal and oil for energy generation, producing 9.5 tons of CO2 per capita in 2015. (3)
Short-term (hours to weeks) exposure to particulate matter < 2.5 µm in diameter (PM2.5) can trigger mortality and nonfatal events related to cardiovascular disease. (20) A study of 25 Italian cities demonstrated that the temperature-related mortality increased threefold when there were high concentrations of fine particulate matter as compared to conditions with low concentrations of fine particulate matter. (21) One meta-analysis, which screened 117 publications and identified 34 appropriate studies, found that short-term exposure to air pollutants was associated with a marginal, but significant increase in the risk of myocardial infarction. (22) The data for longer-term exposure is less clear, however. Pooled data from several European countries showed increased cardiovascular risk for long-term exposure to nitric oxides but not to long-term exposure to PM2.5. (23) A recent meta-analysis showed that long-term exposure to PM2.5 was significantly associated with death from CAD but not with incident myocardial infarction. (24) Several studies have found that short-term (25) and long-term (26) exposure to pollutants increase the risk of heart failure hospitalization and mortality. Finally, short-term exposure to air pollution has been associated with increased risk of atrial fibrillation and ventricular arrhythmia, especially premature ventricular contractions. (6)
Pathways for increased CV morbidity and mortality related to air pollution include systemic inflammation, systemic oxidative stress, increased markers of coagulation and thrombosis, elevation of pulmonary artery pressures, endothelial dysfunction, reduction in heart rate variability, cardiac ischaemia and repolarization abnormalities. (20) It is more than likely that there are a number of complex interactions between many of these pathways which, together with varying duration of exposure to particulate matter and individual susceptibilty, may explain some of the disparity in clinical findings.
Water
Water quality and availability have deteriorated in many parts of Africa. (27) Several studies have shown a decline in water quality in South Africa due to the ongoing pollution caused by urbanization, mining, industry, power generation, afforestation and agriculture. (28) Water shortages and impaired quality will have both direct and indirect effects on cardiovascular health in southern Africa. In addition to direct effects such as dehydration and infectious diseases, lack of water quality and security will have indirect consequences on healthcare delivery. For example, decreasing rainfall levels and droughts have resulted in lower water levels in dams with adverse impacts on hydropower generation. This has resulted in low electrical energy production, high cost of electricity and power outages or load-shedding in some African countries that depend on hydroelectric power generation. These in turn will drive up costs of goods and services and will have an impact on the cost and affordability of healthcare.
Migration & Urbanization
Climate change could affect the size and characteristics of rural and urban human movement in Africa. Increased urbanization due limited economic opportunities and political unrest in rural Africa will have an adverse impact on urban infrastructure and health care systems. (29) In addition, urbanization has been linked to increases in poverty, vulnerability to CVD and increased water and vector-borne diseases. (6,30) The multitude of factors related to migration and urbanization are likely to contribute directly and indirectly to CVD burden, but their interactions are complex. (6)
Climate change and influence of Healthcare
Compared to many service sectors, the healthcare industry is highly energy intensive, particularly in well-resourced countries. It is estimated that the healthcare sector contributes to 2.8% of air pollution and 4.4% of all greenhouse gas emissions. (31) In the United States the healthcare industry is responsible for almost 10% of greenhouse gas emissions. (32) Relative to developed nations, most countries in Africa and their healthcare sectors have a much lower carbon footprint. However, the healthcare sector is a growing industry in developing nations and will probably contribute the same relative greenhouse gas emissions as in developed nations in the future. Thus, it is imperative that the healthcare industry takes steps to reduce its carbon footprint and thereby contribute to reducing the burden of cardiovascular disease. This requires a multipronged approach which includes education, assessment and research of climate-related health consequences and of sustainable healthcare practices.
Mitigating the effects of climate change
A wide scale response to climate change should include both mitigation and adaptation strategies. Mitigation, which refers to efforts to reduce or prevent greenhouse gas emissions, can be achieved by switching to renewable energy sources to power healthcare facilities. Many healthcare facilities in South Africa are privately funded and have the necessary resources to switch their energy needs to be supplied by renewable sources. These facilities can lead the way for the public sector to follow.
A move away from coal and oil towards solar or wind provides a huge opportunity to improve cardiovascular health in South Africa. Patient education regarding moving away from red meat to plant-based diets and encouraging walking or biking versus motorised transport has dual benefits in reducing gas emissions and reducing risk of CVD by promoting more physical activity. Old paradigms need to be rethought. Physicians need to consider other measures such as electronic medical records systems versus paper-based systems. There should be a promotion of telehealth and local ambulatory care and empowerment of self-care over inpatient treatment. Many of these strategies were used highly effectively during the COVID-19 pandemic.
As the threat of climate change is an existential one to the world it is imperative that education regarding climate change and its effects on health should be incorporated in the training of every healthcare professional in Africa. Furthermore, physicians should become advocates for change for climate policies not only at their local hospital levels but also at municipal, provincial and national levels.
Conclusion
The effect of climate change on cardiovascular health is multi-faceted and complex. There is growing data that the consequences of climate change increase the risk for adverse cardiovascular events, particularly in vulnerable individuals and patients with underlying cardiovascular disease. Urgent steps are required to mitigate climate change in order to limit an already over-burdened healthcare system. To quote Druve Kazi, from Harvard Medical School, “Just as we are passionate about controlling lipids and blood pressure, we should feel passionately about controlling climate related risk”.
