Air Pollution and Increased Risk of Heart Disease and Stroke
Two Health Problems Caused by Air Pollution
Someone who is at risk of developing heart disease or experiencing a stroke is probably very familiar with their doctor's recommendations to help them stay healthy. The person is usually advised to follow a nutritious diet that is low in sugar, salt and unhealthy fats. The doctor will likely recommend that the person lowers the amount of LDL cholesterol in their blood, exercises regularly, avoids smoking and limits their alcohol consumption. However, there's another aspect of our daily lives that can affect the risk of cardiovascular problems - the air that we breathe. Air pollution has repeatedly been linked to a higher risk of heart disease and strokes.
Both outdoor and indoor air pollution can cause heart, blood vessel and circulatory problems. This pollution consists of both gases and fine particles. Luckily, there are steps that we can take to reduce (but not eliminate) our exposure to air pollution. These steps are important for all us, but they are especially important for people who already have a cardiovascular problem.
Pollution, Blood Pressure and Heart Rate
Outdoor Air Pollution, Heart Disease and Strokes
It's been known for some time that air quality can influence the chance of developing cardiovascular problems. In the United States, the EPA (Environmental Protection Agency) has published a document describing the relationship between outdoor air pollution, heart disease and circulatory system disorders.
In people with certain pre-existing medical or physical conditions, air pollution can trigger irregular heart rhythms (arrhythmias), a heart attack or a stroke. There is also a small risk that apparently healthy people will develop cardiovascular problems due to inhalation of pollutants.
The EPA says that the most dangerous pollutants with respect to circulatory heath are the tiny particles that are present in smoke, smog, dust and haze. People who have a higher risk of being affected by these particles include those who have already suffered from a heart attack or a stroke, people who have had heart surgery, people with angina or other heart problems and people with blocked arteries, diabetes or chronic obstructive lung disease (also known as chronic obstructive pulmonary disease, or COPD).
Other factors which may increase the chance of cardiovascular damage due to air pollution include having a high blood cholesterol level or high blood pressure, smoking, being overweight, not exercising, and being a woman aged 55 or older or a man aged 45 or older. Having a family member who experienced heart disease or a stroke at a relatively early age (younger than 55 in a father or brother and younger than 65 in a mother or sister) also increases the risk.
LDL cholesterol increases the amount of plaque in arteries while HDL cholesterol removes plaque. Plaque can block the arteries. Some researchers say that we should consider the ratio of HDL to LDL cholesterol in the blood instead of just the total amount of cholesterol when we are assessing someone's health.
Outdoor Pollution Overview
Quantitative Data - Air Quality and Cardiovascular Problems
The observation that air pollution increases the chance of heart disease and strokes has been made many times, but some scientists are trying to get quantitative data to support this observation. Two examples of this data are described below.
One statistical survey was completed by researchers at the Sackler Faculty of Medicine at Tel Aviv university. Dr. Yariv Gerber and his colleagues examined the records of patients admitted to hospital after suffering a myocardial infarction (heart attack) and then followed their medical progress for nineteen years. Air quality was also monitored in the areas where the patients lived. The researchers found that patients living in the most polluted areas were 43% more likely to experience a second heart attack or congestive heart failure and 46% more likely to experience a stroke. They were also 35% more likely to die in the nineteen year study period.
Dr. Hazrije Mustafic and colleagues at the Paris Descartes University examined data from the general population. They found that short-term exposure to air pollution (no more than seven days in length) produced a statistically significant increase in the risk of a heart attack. The pollutants included particulate matter, sulfur dioxide, nitrogen dioxide and carbon monoxide. Exposure to ozone didn't increase the risk of a heart attack. Ozone is known to cause breathing problems, however.
Inhaled Pollutants and Blood Vessel Changes
In the USA, researchers analyzed ten years of data from a Boston Stroke Center. The records of 1,705 patients were studied. The researchers found that strokes were more likely to occur after a twenty-four hour period in which the air quality had dropped into the "moderate' range, as classified by the EPA. There was a 34% increase in stroke risk after a day of "moderate" air quality as compared to the risk after a day of "good" air quality. The air quality did not need to be as bad as that shown in the photo at the top of this page in order to have a detrimental effect.
A stroke is a disorder in which the blood flow to part of the brain is stopped or severely reduced. The condition may be caused by a blocked artery (ischemic stroke) or by a broken blood vessel (hemorrhagic stroke). Both situations are medical emergencies.
What is Indoor Air Pollution?
Indoor Air Quality and Heart Disease
Indoor air pollution can also increase the risk of heart disease. The pollution may consist of cigarette smoke, particles released from wood-burning stoves, fireplaces, candles or incense, vapors from household cleaning products, painting products, pesticides, carbon monoxide, and outdoor pollution that finds its way indoors. Formaldehyde and radon may also be present as pollutants, and so may mold spores.
Health Problems Caused by Indoor Pollutants
Secondhand smoke is especially dangerous for cardiovascular health, since cigarette smoke increases the risk of both heart attacks and strokes. Burning wood releases tiny carbon particles which may cause shortness of breath and contribute to circulatory and heart problems, especially in older people. The vapor from paint solvents and some pesticides can cause an irregular heartbeat. Exposure to dust from paints containing lead can cause high blood pressure.
Carbon Monoxide and Heart Disease
Carbon monoxide joins to hemoglobin, the red pigment in our blood that normally attaches to oxygen and transports it around the body to all the tissues. The carbon monoxide prevents oxygen from binding to hemoglobin molecules, which means that the body's cells won't receive the oxygen that they need to survive. Even a small amount of carbon monoxide will interfere with the blood's ability to transport oxygen and can lead to chest pain and heart arrhythmia.
Carbon monoxide may be emitted from space heaters, ranges, dryers, fireplaces and wood stoves. It's also released from the exhaust of motor vehicles. The gas can build up when a vehicle is left in a garage or other enclosed space with its engine running. This can be true even if the garage door is open.
Carbon Monoxide Poisoning
How Does Air Pollution Affect the Cardiovascular System?
There are several suspected reasons why exposure to air pollution can increase the risk of a heart attack or stroke. Some studies have shown an increased heart rate after inhalation of polluted air. In addition, studies have shown detrimental blood vessel changes in people chronically exposed to air pollution. In atherosclerosis, fatty deposits known as plaque collect in the lining of arteries, causing the arteries to become stiff. Air pollution speeds up the progression of atherosclerosis.
Particles less than 2.5 microns in diameter are especially worrying for researchers. (A micron is a millionth of a meter, or a thousandth of a millimeter.) These tiny particles easily enter the human body and irritate both the lungs and the arteries serving the heart muscle.
Researchers have discovered that the level of C-reactive protein (or CRP) increases in at least some people exposed to air pollutants. A high level of this protein is an indication of inflammation inside the body, sometimes including inflammation of arteries, and has been linked to heart disease. In fact, the blood level of the protein is sometimes tested in order to assess a person's risk of cardiovascular problems.
C-reactive protein is made by the liver. It's a "marker" for inflammation - that is, a substance which indicates that inflammation is present. It has sometimes been suggested that the protein is also a cause of inflammation, but the evidence obtained so far doesn't support this idea.
How to Avoid Air Pollution
Avoiding Outdoor Air Pollutants
Besides maintaining a healthy diet and lifestyle (and seeking a doctor's advice about the amount and frequency of exercise that is appropriate for a specific medical condition), there are a number of steps that we can take to protect ourselves from injury caused by outside air pollution.
First, it's a good idea to follow the daily reports of air pollution levels. Pollution doesn't have to be visible to be harmful. In many cities there are news programs on the television or radio that report on the air quality each day. There are websites that do the same thing. A useful site for people living in the United States is the AIRNow website, which describes the current air quality. There's a link to the Canadian version of the site on the AIRNow home page.
Even when the air quality is reported to be good, there are some precautions that are useful for people who have serious cardiovascular problems. It's a good idea to do outdoor exercise away from traffic, or at least to avoid busy traffic, since the exhaust released by vehicles contributes to air pollution. Areas near industries that release products into the air should also be avoided. It's also advisable to stop outdoor exercise when there is a forest fire producing smoke. If someone does exercise in polluted air, it's good to do a gentler form of exercise that involves slower and shallower breathing than a more energetic exercise.
Avoiding Indoor Air Pollutants
Indoor air pollution can be greatly reduced by not allowing smoking in a home. Containers of cleaning materials and pesticides should be kept tightly closed and far away from the living area. It's a good idea to use fragrance-free products to reduce the release of volatile compounds into the environment. Furnaces, heat-producing devices and devices that use fuel should be serviced regularly to make sure that they're operating correctly and aren't releasing dangerous fumes. They should also be well ventilated.
Installing carbon monoxide (CO) alarms is a great idea, especially next to a sleeping area. Carbon monoxide is a sneaky poison. It's invisible and has no odor, so people are usually unaware that they are inhaling it. It produces symptoms that may be confused with the flu, such as a headache, dizziness, nausea, weakness, tiredness and confusion. An affected person may eventually lose consciousness if the concentration of carbon monoxide is high enough.
While it's very important that countries and communities take steps to reduce air pollution, it's also important that we as individuals try to reduce both our production of substances that add to air pollution and our exposure to this pollution. Our health may depend on it.
Surveys About Heart Problems and Air Pollution
Air Quality in Relation to Heart Disease and Stroke
The Role of Outdoor and Indoor Air Pollution on Cardiovascular Problems
- Uzoigwe JC, Prum T, Bresnahan E, Garelnabi M. The Emerging Role of Outdoor and Indoor Air Pollution in Cardiovascular Disease. North American Journal of Medical Sciences. 2013;5(8):445-453. doi:10.4103/1947-2714.117290.
© 2012 Linda Crampton