The research, a sub-analysis of a Canadian-led study of more than 29,000 subjects in 52 countries on six continents, also found that owning both a car and TV upped the risk of having a heart attack even more — but only in low- and middle-income nations.
"Much is already known about the association between physical activity and cardiovascular risk, but what this study adds, among many other things, is a global perspective," said lead author Dr. Claes Held of Uppsala University Hospital in Sweden.
"Physical activity does protect you from the risk of heart attack and it's consistent across the globe," Held said in an interview Tuesday from Uppsala. "So it's a global risk factor to be physically inactive."
Held said the study shows that mild to moderate physical activity at work, and any level of physical activity during leisure time, reduces the risk of heart attack, independent of other risk factors such as having diabetes, high blood pressure or smoking, in men and women of all ages in most regions of the world.
But interestingly, the researchers found that performing heavy physical labour as part of a job did not protect against heart attacks.
"I think — I say think because we don't know — it might be that this group with heavy labour that the result is confounded by other factors that we don't know about," said Held, speculating that such participants might work in unhealthy environments with high physical stress.
"We know a trigger of heart attack can be heavy physical work such as if you're shovelling snow or doing sudden strenuous activity," he added.
The findings, published in the European Heart Journal, come from the INTERHEART study led by principal investigator Dr. Salim Yusuf of McMaster University in Hamilton.
This analysis compared the work and leisure exercise habits of 10,043 people who had suffered their first heart attack with 14,217 healthy people. They asked participants whether their work was mainly sedentary, involved predominantly walking on the same level, walking that included going uphill or lifting heavy objects, or heavy physical labour.
For physical activity during their leisure time, participants could select from four possible responses: mainly sedentary (such as sitting reading, watching TV), mild exercise (such as yoga, fishing, easy walking), moderate exercise (walking, cycling, for instance) or strenuous exercise (running, football or vigorous swimming).
After adjusting for a variety of factors, they found people whose work involved either light or moderate physical activity had an 11 to 22 per cent lower risk of having a heart attack, compared to those whose occupation was mainly sedentary.
During leisure time, the risk of a heart attack was lower for any level of exercise when compared with being mainly sedentary, down by 13 per cent for mild activity and 24 per cent for moderate to strenuous activity.
A higher proportion of people in low-income countries had sedentary jobs and did less physical activity in their leisure time than those in middle- and high-income countries, say the authors, who speculated that the difference may be partly explained by cultural, educational and other socio-economic factors, as well as living in warmer climates.
The researchers also asked subjects about the ownership of goods such as a car, motorcycle, radio-stereo, TV, computer, land and livestock.
They found that people who owned both a car and television had a 27 per cent higher risk of having a heart attack compared to those who owned neither.
"Ownership of a car and TV, which promotes sedentary behaviour, was found to be independently associated with the risk of heart attacks," said Held.
Yet the finding was confined to people who lived in low- and middle-income countries, not high-income nations like Canada — but why?
"We have to speculate about it, but maybe in the high-income countries we do more physical exercise when we're off work, so even though we probably drive cars more and probably watch TV more than those in countries with a low- or middle-income, we might still be more active in total," said Held.
"People ask me: 'Should I sell my car or sell my TV,' and that's not the interpretation ... We have to keep in mind these are associations."
Surprisingly perhaps, owning a computer did not correlate with a higher heart attack rate, a finding that would need more research to explain, he said.
The bottom line, said Held, is that being physically "is a very simple and easy way to stay healthy ... and it's not like extreme levels of activity are needed."
In an accompanying editorial, Drs. Emeline Van Craenenbroeck and Viviane Conraads of Antwerp University Hospital in Belgium agree with that assessment.
"If we want to support healthy longevity, we should put a stop to the pandemic of sedentarism," they write. "Staying physically fit throughout life may well be one of the easiest, cheapest and most effective ways to avoid the coronary care unit."