Image copyright AP 
 
 Every winter, about 100 people in the US die while shovelling snow. Why? 
 
 A study looking at data from 1990 to 2006 by researchers at the US Nationwide Children's Hospital recorded 1,647 fatalities from cardiac-related injuries associated with shovelling snow. In Canada, these deaths make the news every winter. 
 
 Cardiologist Barry Franklin, an expert in the hazardous effects of snow removal, believes the number of deaths could be double that. "I believe we lose hundreds of people each year because of this activity," says Franklin, director of preventative cardiology and cardiac rehabilitation at William Beaumont Hospital, Michigan. 
 
 His team found that when healthy young men shovelled snow, their heart rate and blood pressure increased more than when they exercised on a treadmill. "Combine this with cold air, which causes arteries to constrict and decrease blood supply, you have a perfect storm for a heart attack," he says. 
 
 The Answer raises blood pressure and heart rate more than some other forms of exercise 
 
 cold air constricts blood vessels 
 
 cardiac risks are higher in early morning 
 
 rare exercise for sedentary over-55s 
 
 Snow shovelling is particularly strenuous because it uses arm work, which is more taxing than leg work. Straining to move wet and heavy snow is particularly likely to cause a surge in heart rate and blood pressure, Franklin says. 
 
 Many people hold their breath during the hard work, which also puts a strain on the body. In addition, the prime time for snow clearance is between 6am and 10am which is when circadian fluctuations make us more vulnerable to heart attacks. 
 
 Franklin considers snow shovelling to be so dangerous that he advises anyone over the age of 55 not to do it. 
 
 Image copyright AP 
 
 "People at greatest risk are those who are habitually sedentary with known or suspected coronary disease, who go out once a year to clear snow," he says, adding that smoking and being overweight drastically increase the risk. If you must do it, push rather than lift the snow, dress in layers, take regular breaks indoors and don't eat or smoke before shovelling, he advises. 
 
 Using a snow blower is a better option, but there have also been heart attacks recorded in men using blowers, including one fatality in Buffalo on Wednesday. "People don't have any idea how taxing it is on the heart," Franklin says. 
 
 Reporting by Jo Jolly 
 
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– Before you break out the snow shovel this season, doctors say there are a couple of things to keep in mind lest clearing your walk turn deadly. At least two people died from heart problems while shoveling snow this week in Buffalo and about 100 Americans meet the same fate each year, the BBC reports, as a boosted heart rate and artery-constricting cold air make "a perfect storm for a heart attack," a doctor explains. If you're over 55 or "habitually sedentary," he says you shouldn't pick up a shovel at all. Shoveling snow is also risky for smokers and people with coronary disease. But if you have to shovel, remember to breathe during the exercise. Push the snow, don't lift it, and avoid the 6am to 10am window if possible as hormone levels make people particularly prone to heart attacks at that time. Dress warmly and take regular breaks inside, the doctor advises. The American Heart Association chimes in with a few additional tips: Skip big meals right before or after shoveling, as a heavy meal can tax the heart. And in terms of your shovel, use a smaller one; the less snow you move at once, the safer you'll be. And if you're looking to warm up, avoid alcohol, a doctor tells ABC News. "It puts the heart at more risk." The advice, which also applies to those who use snow blowers, will come in handy if you're planning to help out the Buffalo Bills. (Click for more shoveling tips.)