Extreme temperatures, pollution raises risk of cardiac arrests

Many people feel sluggish or experience difficulty in breathing while carrying out routine work in extreme hot or cold conditions, or on days of heavy pollution. Now a new international study confirms that everyday activities such as lifting, carrying moderately heavy items, and walking up an incline, are significantly more taxing in extreme temperatures and pollution.

The study also suggests that the increased stress during extreme temperatures could even trigger a cardiovascular event and raise the risk of fatal heart attacks. A global analysis estimated that heat could be responsible for 490,000 excess deaths each year According to the World Health Organization (WHO), as climate change continues to worsen if no adaptation is undertaken, the heat-related excess mortality is expected to almost triple between 2030 and 2050.

A study that looked at more than 202,000 heart attack deaths in the Chinese province of Jiangsu between 2015 and 2020, noted a ‘significantly associated’ risk that a person would die from a heart attack if temperatures were extremely hot or cold, or there were high levels of pollution from particulate matter (PM) — particles of solids or liquids in the air, such as smoke, dust, or dirt.

The study classified extremely hot weather as temperatures significantly above the average for a given area and season, consistently greater than the 90th percentile. Extremely cold weather, on the other hand, is characterized by temperatures significantly below the average for a given area and season, consistently below the 10th percentile.:

Extreme heat triggers physiological responses to help the body adapt and survive — notably, sweat and dilation of blood vessels close to the skin’s surface. This causes the heart to work harder and faster to maintain adequate blood flow to vital organs, which consequently places increased workload and additional stress on the heart.

In hotter temperatures, people can also become easily dehydrated, which can increase the risk of heart attack. Dehydration can lead to a syndrome known as syncope, where a person loses consciousness due to lack of blood to the brain. Extreme heat, particularly dehydration, can exacerbate issues of syncope. Additionally, dehydration can indirectly make blood more prone to clotting, potentially leading to blockages in coronary arteries, thus triggering a heart attack.

Cold weather is also tough on the heart, but for different reasons. Cold weather induces vasoconstriction — narrowing of the blood vessels — and consequently raises blood pressure levels and reduces the oxygen supply to the heart. As your body works to keep you warm, it adds increased stress on your heart. Similar stress is also placed on the heart under heavy air pollution

Although air pollution risks are often centered around the lungs and respiratory health, healthcare providers say it can also affect the heart, largely because the body’s vital organs work together. What affects one can affect another. The WHO has recognized air pollution as a risk factor for noncommunicable diseases such as ischaemic heart disease, stroke, chronic obstructive pulmonary disease, asthma and cancer.

Clean air is fundamental to good health, says WHO. noting that 6.7 million deaths each year are attributable to exposure to ambient and household air pollution. Data from the health organization also showed that in 2021, more than 2.3 billion people continued to rely primarily on polluting fuels and technologies for cooking.

PM2.5 particles are tiny particles that float in the air, risking inhalation deep into the lungs or entrance into the bloodstream. Once in the body, these particles can cause inflammation and oxidative stress, leading to damage to blood vessels and the heart. PM2.5 exposure is also associated with the development and progression of atherosclerosis — the buildup of plaque in arteries, which increases the risk of heart attacks.

High pollution days may be classified as those where PM2.5 levels, often measured in micrograms per cubic meter (μg/m3 ), exceed specific guidelines set by health organizations. According to the WHO, around 99 percent of the world’s population live in places where air pollution levels exceed WHO guideline limits of annual mean concentrations of PM2.5 not exceeding 5 μg/m3.

Specific cohorts of the population are at a higher risk for a fatal heart attack during extreme heat or cold or when there are high levels of air pollution. These include people with pre-existing cardiovascular conditions, like coronary artery disease and hypertension, pregnant women; people with diabetes; elderly individuals, and the very young.

However, doctors advise everyone to take precautions during extreme weather or if there is a high amount of air pollution. To protect yourself in extreme heat, experts recommend staying hydrated by drinking plenty of water; seeking shade or air-conditioned environments, when possible; modifying workouts; and avoiding peak heat, which is usually hottest between 10am and 4pm, as the risk of overexertion and stress on the heart is highest during this period.

Most importantly, listen to your body. rest in a cool place if you experience warning signs like dizziness or weakness, and seek medical help if symptoms persist or worsen.

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