Dr Martin Juneau, M.D., FRCP
Cardiologue et Directeur de la prévention, Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.See all articles
Updated March 22, 2019
A century ago, every aspect of daily life involved a physical effort, both at work and at home, but today mechanization and modern technologies have made it possible to replace this type of work with activities that are much less physically demanding. A study estimated that the level of activity associated with the lifestyle of Australian settlers in the early 19th century was 1.6 to 2.3 times higher than that of the modern lifestyle, a huge difference, equivalent to walking 8–16 km every day. Nowadays, people who drive to work, take the elevator to get to their office, and spend most of their day in front of a computer hardly use their muscles during the day, a situation that can worsen if they spend the rest of their day on passive leisure activities, e.g., in front of a screen (television, telephone, tablet, computer).
According to Statistics Canada, adults spend an average of 9 hours and 48 minutes of their waking hours each day on sedentary activities, without any physical effort. In 2012 and 2013, barely 22% of the Canadian population met the recommended minimum of 150 minutes of moderate-intensity physical activity per week, a proportion that becomes even lower (12%) among those aged 60 and over. This modern sedentary lifestyle has serious consequences for the health of the population: for example, a study conducted in Australia with more than 8,800 people showed that those who watch television for more than four hours a day are 80% more likely to die from cardiovascular disease (CVD) than those who watch it less than 2 hours a day. Australian researchers estimated that each hour spent in front of the television increases the risk of dying from heart disease by 18%. Unfortunately, according to the Canadian Radio-television and Telecommunications Commission (CRTC), Canadians spend an average of 27.2 hours per week in front of the television (42 hours for the 65 and over age group). An increase in the risk of type 2 diabetes and certain cancers has also been observed in compulsive television watchers, illustrating the fact that being inactive for prolonged periods can have negative repercussions on health.
It is now well established that regular physical activity plays a very important role in the prevention of many chronic diseases, including cardiovascular disease, certain types of cancer, osteoporosis, diabetes, obesity, hypertension, dyslipidemia, depression, stress and anxiety. Not only are the benefits of physical activity numerous, but the amount of exercise required to take advantage of these benefits is much lower than one might think. This is particularly well illustrated by the results of a very large study conducted in Taiwan. By examining the physical activity levels of almost half a million men and women for eight years, researchers found that as little as 15 minutes of moderate physical activity per day (walking for example) is sufficient to significantly reduce the total number of deaths, as well as the mortality rate associated with cardiovascular disease, diabetes and certain cancers. Obviously, the magnitude of these benefits will be even greater if one increases the duration and the intensity of the physical activity performed (Figure 1).
Figure 1. Comparison of the benefits of running and walking. From Wen et al., 2014.
For example, if 15 minutes of moderate activity such as walking reduces the risk of premature death by 8%, this risk will be reduced by 15% if you walk for 30 minutes, to reach a maximum of about 35% for 90 minutes of walking per day. The point to remember, however, is that the simple fact of ceasing to be sedentary and moving, even very slightly, provides measurable health benefits.
A study of 88,140 Americans aged 40 to 85, followed over a 9-year period, shows that there is an association between doing a little physical activity during leisure time and reducing the risk of death from any cause. In fact, compared to inactive people, those who did 10 to 59 minutes of moderate-intensity physical activity per week during their leisure time (brisk walking, for example) had an 18% lower risk of all-cause mortality and a 12% lower risk of cardiovascular mortality. For people who exercised at a moderate-intensity level for a longer period of 150 to 299 minutes/week, the risk of death from any cause decreased even further: 31% for all-cause mortality and 37% for cardiovascular mortality. In this study, individuals who engaged in vigorous-intensity activity reduced the risk of mortality more than those who exercised at moderate intensity.
These benefits are not limited to physical activity done during leisure time. For example, in a study conducted in Japan, total physical activity levels (including housework, commuting, recreation, etc.) were examined in 74,913 participants aged 50 to 79 years. The researchers found that a moderate level of physical activity (5-10 MET-h/day [Metabolic Equivalent of Task]) reduces the risk of cardiovascular disease by about 30% compared to those who reported a very low level of physical activity. An activity level of 5 MET-h/day corresponds to approximately 90 minutes of walking at a moderate speed [4.8 km/h] per day. This level of physical activity seems to be sufficient to achieve maximum effect since higher levels of physical activity [10 to 35 MET-h/day] did not further reduce the risk of CVD. The benefits of physical activity are thus within everyone’s reach and simply doing moderate activities in our daily routine, such as walking, gardening and housework, is enough to significantly reduce the risk of cardiovascular disease, provide a host of health benefits, and significantly improve quality of life.
Pollution, physical activity and risk of myocardial infarction
Physical activity increases the absorption of air pollutants, which could potentially reduce its beneficial effects. A Danish population study examined whether the benefits of physical exercise on the risk of myocardial infarction were reduced by air pollution. People living in the most polluted areas of the country, where the level of exposure to nitrogen dioxide (NO2) was highest, had an increased risk of 17% of having a myocardial infarction and an increased risk of 39% recurrence, compared to people living in less polluted areas. Physical activity was associated with a significant reduction in the risk of heart attacks for all participants: -15% for sports, -9% for cycling, -13% for gardening. The results are not significantly different when participants living in polluted areas (NO2≥ 21 μg/m3) are compared to those living in less polluted areas (NO2<14.3 μg/m3). In other words, physical activity reduces the risk of myocardial infarction in both polluted and less polluted environments. The authors of the study still suggest avoiding, as much as possible, exercising in a polluted environment, for example by avoiding busy urban roads and instead choosing less polluted secondary streets.