02 September 2010

A jog in the smog

How does urban pollution affect people who exercise outdoors?


I regularly cycle up Cape Town's Kloof Nek Road in the late afternoon, and regularly fret all the way up the hill about the amount of pollution I’m sucking in. With this weighing on my mind, a couple of mornings ago I got up in the winter gloom and hit the road at about 7:45am instead.

I felt noble, greeting the sunrise through the cold and mist, the plume of my breath mingling romantically with the car exhausts.

Afterwards, I also felt silly: strenuous cycling on a cold misty morning at rush-hour isn’t really any better for you than strenuous cycling in the afternoon rush-hour.

So what’s the answer? Drive everywhere and to hell with the environment? Stay cooped up indoors? Start smoking because you're doing that anyway just by going for a run?

What those fumes do to you
Unless you walk around with your own personal air tank, if you live in a city you’re affected by air pollution.

Of the various sources of urban pollution, road traffic is usually the worst offender.

Motor vehicle exhaust contains a large number of pollutants, including undesirables such as carbon monoxide (the odourless 'suicide gas'); nitrogen oxides (you can smell these, and see them too – they’re a big part of ‘brown haze’); particulates (tiny airborne solids and liquids - the bigger ones add to haze, but the smaller ones penetrate deep into our respiratory systems); and hydrocarbons like the carcinogen benzene. Hydrocarbons and nitrogen dioxide combine in the presence of sunlight to form ground-level ozone (the ‘bad’ ozone), a major component of smog.

Many of these toxins can cause immediate symptoms like coughing, wheezing, chest pain, headache, sore eyes and sore or itchy throat.

Repeated long-term exposure may increase the risk for chronic lung damage, infection (because of lowered immunity), heart disease, cancer and neurological problems.

Certain groups – children, the elderly, and people with heart or lung conditions – are particularly vulnerable to air pollution’s ill-effects.

Drivers aren’t immune
Surprisingly, air pollution exposure is generally not worse for pedestrians and commuter cyclists compared with motorists.

If you think you’re immune because you drive around with the windows up and the aircon on, think again: studies on pollutant levels for different road users show that the atmosphere drivers breathe inside their cars isn’t always better – and often it’s worse – than that breathed by a pedestrian on the pavement outside.*

Exercisers at higher risk
Strolling along the pavement is one thing, however; jogging along it (or toiling up Kloof Nek Road) puts you in a rather different risk category.

When exercising, you breathe in much more air and pull it more deeply into your lungs – which means you take in more pollutants in that air. Also, when you’re doing intense aerobic exercise, you breathe mainly through your mouth, which doesn’t have the natural filtration effect of nose-breathing.

Don’t stop exercising!
This all sounds pretty grim, but most doctors would agree that the health benefits from exercise outweigh the potential dangers of air pollution. And you can reduce your exposure considerably:

  • Avoid exercising near areas of heavy traffic. Choose quieter roads, parks or sports fields.
  • Early morning and evening (before and after peak traffic i.e. before 7am and after 7pm) are generally the best times for outdoor exercise. Of course, in mid-winter this means being on the streets in the dark; if safety’s a concern then get a group together. But at least do try to avoid exercising in the afternoon, when ozone has had time to form, especially on sunny, hazy, windless summer days.
  • Still winter mornings are also often conducive to higher pollution levels. In some areas, an inversion layer forms: cold air and pollutants get trapped at ground level by a higher layer of warmer air. This effect weakens as the ground heats up during the day.
  • The wind and rain are your friends. Wind can sometimes blow pollution from a fixed source (e.g. a smoke-stack) in your direction, but generally wind is a great help in dispersing pollution. Rain literally washes pollutants out of the air, so post-rainstorm is a good time for outdoor activities.
  • If you must exercise when pollution levels are high, decrease your workout’s duration or intensity, or both – and make up for it on a less polluted day.
  • Remember that outdoor exercise can also include vigorous DIY or gardening, and children’s play.
  • Call your local health department to find out if they do air quality reports, or if they can give you information about when and under which conditions pollution is most problematic in your area.
  • Tobbaco smoke contains many of the same pollutants found in exhaust fumes, in an even more potent form. Reduce your overall pollution exposure by being vigilant about indoor (and 'in-car') pollution too: avoid smoky interiors and sitting behind the wheel in rush-hour traffic. This becomes even more important just before a sports competition or a heavy training session.
  • Give your body a pollution (and stress) break with an occasional weekend in the country.

- Olivia Rose-Innes, EnviroHealth Expert, Health24, updated August 2008

Read more:Beijing pollution ups heart risks


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