Dear Doctor Column, May 21, 2007

Outdoor Exercise and Air Pollution

Question:

I like to jog outdoors, even in the summer heat. I’m healthy and in good shape. Is it safe for me to exercise outside on ozone alert days?

Hot, sunny, summer days produce just the right conditions for formation of ground-level ozone, created when sunlight sets off a chemical reaction between oxygen and pollution emitted from cars, refineries, power and chemical plants, and other sources. Ground-level ozone aggravates the respiratory system and can cause coughing, chest pain, and an irritated throat. In addition, long-term exposure to ozone can reduce lung function, which can make breathing shallow and uncomfortable, and inflame the lining of the lungs.

Some people are more susceptible to damaging effects of ozone than others. Children, the elderly, and people with asthma are most vulnerable. Ozone also can worsen symptoms in people with respiratory diseases such as bronchitis and emphysema. Individuals with diabetes and congestive heart failure may also be more sensitive to ozone pollution.

However, when ground-level ozone levels are high, even healthy individuals can experience breathing problems. Being aware of air pollution is a good idea for everyone who spends time outdoors in the warmer months and is especially important if you are physically active outside.

The Air Quality Index (AQI) can tell you how clean — or polluted — the air is in your area. Developed by the Environmental Protection Agency, the AQI index calculates levels of the five major types of air pollution: ozone; particulate matter, produced by motor vehicles, power plants, forest fires, and other types of combustion; carbon monoxide — car exhaust is the major source, accounting for 95% of carbon monoxide in urban areas; sulfur dioxide, a byproduct of some industries; and nitrogen dioxide.

The AQI is split into six color-coded categories running from 0 to 500. Higher numbers mean more air pollution. When levels are between 0 and 50 (green), air quality is good. Levels between 50 and 100 (yellow) are not considered harmful, although a few people who are unusually sensitive to air pollution may experience breathing problems. Numbers between 101 and 150 (orange) indicate air pollution has reached unhealthy levels for people who are in sensitive groups, such as those with lung and heart disease. AQI values of 151 to 200 (red) mean the air is unhealthy for everyone, and people who are especially sensitive to pollution may begin to experience more serious respiratory symptoms.

AQI values between 201 and 300 (purple) trigger a health alert warning that everyone can experience serious symptoms, and levels higher than 300 (maroon) indicate emergency conditions that can affect the entire population. AQI values above 200 are uncommon, even in large cities with pollution problems, and values above 300 are extremely rare, the EPA reports.

Being aware of AQI levels can help you reduce the risk of health problems associated with air pollution. In the summer, many local newspapers print AQI values and most weather reports provide warnings when air quality reaches unhealthy levels. The EPA maintains a site with general information about air pollution and real-time and forecast air quality data. Go to the EPA site to check air quality in your area.

Exercise increases the effects of air pollution because you are drawing more of the potentially harmful substances into your lungs. In the summer, people with lung or heart disease should consider exercising indoors in an air conditioned environment. Healthy people who want to exercise outside can reduce their exposure to pollution by following some simple steps when air quality is poor:

• Work out in the early morning or late afternoon/early evening when air pollution is usually at its lowest levels.
• Cut back on heavy exertion by reducing the time and intensity of your workout. For example, if you usually jog for 45 minutes, try walking for half an hour instead. If you have any trouble breathing or experience chest pain or unusual coughing, stop exercising and see your doctor.
• Avoid jogging on roads with heavy traffic. The carbon monoxide produced by car and bus exhaust competes with oxygen and overexposure can cause headache, dizziness, and dangerous increases in body temperature.
• Be aware that children who spend a lot of time playing outdoors in the summer are especially susceptible to air pollution.

Source: EPA