Monique Keiran: Take a walk at just the right speed

Nature Boy often urges me to slow down. While he scurries along on our walks through the neighbourhood, he often pulls at me and suggests that I pause and smell a flower, look at a bird or examine a passing beetle. It’s his strategy for keeping me to a pace similar to his.

But his attempts to slow my pace on city streets might be good health advice. Recent research indicates that pedestrians who move at two to six kilometres per hour on city roads minimize their inhalation of air pollution while still getting health benefits.

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“The faster you move, the harder you breathe and the more pollution you potentially inhale,” says Alex Bigazzi, the University of British Columbia researcher who analyzed the study’s data, “but you also are exposed to traffic for a shorter period of time. This analysis shows where the sweet spot is.”

Using a U.S. census-based computer model of 10,000 people, Bigazzi calculated ideal travel speeds for different ages, genders, activities and road grades. His results indicate pedestrians under age 20 should walk at speeds of about three kilometres per hour to breathe in the least amount of pollution during a trip. Older people can afford faster paces, at speeds of four to six kilometres per hour, to maintain similar pollution-versus-exercise balances. The steeper the road, the lower the advised travel speed.

For female cyclists under age 20, the speed linked to the least pollution risk is 12.5 kilometres per hour on a flat road. For male cyclists in the same age group, it’s 13.3 kilometres per hour. Bigazzi’s calculations indicate female and male cyclists in the 20 to 60 age group should travel at 13 and 15 kilometres per hour.

The good news, Bigazzi says, is the ideal speeds “align pretty closely with how fast most people actually travel.”

According to a 2013 report published in the Canadian Medical Association Journal, about 21,000 Canadians die prematurely from the effects of air pollution each year — almost nine times the number of deaths from traffic accidents. Such air pollution triggers “inflammation, oxidative stress and imbalance in the autonomic nervous system” and can include heart-rhythm disturbances.

Exercise confers many health benefits, but exercising in polluted air counters them. A recent Columbia University study showed that New York City children who engaged in vigorous daily exercise inhaled more black carbon, a pollutant found in diesel exhaust, than less active children. While physically active kids typically experience less airway inflammation than less active kids do, exposure to black-carbon air pollutants offsets this benefit.

Obviously, pollution levels vary by location and amount of traffic and industry. Other UBC research suggests children whose mothers lived close to highways during pregnancy are 25 per cent more likely to develop asthma before age five than children whose mothers experienced limited exposure to traffic-related pollution. Furthermore, children exposed to significant amounts of outdoor air pollution during their first year of life are more likely to develop allergies to food, mould, pets and pests.

The West Coast has some of Canada’s cleanest air, but it isn’t found uniformly across the region. The Capital Regional District’s anti-idling bylaw helps reduce air pollution from vehicles, but anyone living or working within 100 metres of a major road in Greater Victoria is exposed to fumes from as many as 13,000 vehicles each day, with traffic counts determined by the CRD’s online site.

If you live or work near the Pat Bay Highway, you breathe in fumes from as many as 30,000 vehicles each weekday. If you live near the Trans-Canada Highway west of McKenzie Avenue, you’re exposed to fumes from more than 80,000 cars per day — a number expected to increase in coming years.

So, if you cycle to work along the Galloping Goose every day, make time to travel at the ideal minimum pollution-dose speed.

By commuting at 12.5 to 15 kilometres per hour, you’ll breathe in fewer toxins from the highway traffic rushing by a few metres away. And if you walk to work along any of the region’s busy roads, a slower pace will also help you enjoy the sight of a perching bird, a scuttling beetle and spring blossoms.

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