What is the evidence?

There is ample evidence supporting the beneficial effects of physical activity and exercise, for both physiological and psychosocial health. The WHO state that approximately 3.2 million deaths each year are attributable to insufficient physical activity, and they list insufficient physical activity as one of the 10 leading risk factors for death worldwide. It is apparent that physical activity is extremely important for health. But exactly how strong is the evidence? In this video, we will discuss the strength of evidence on the effectiveness of physical activity in primary and secondary prevention of several chronic diseases and all-cause mortality. So what do we mean when we say all-cause mortality? All-cause mortality is a study outcome.

It means that investigators noted how many patients passed away within a certain period or by a certain age, regardless of the cause of their death, and then carry out an analysis to determine if certain factors, in this case being physically active or fit, increased or decreased their risk of death. Even if the cause of death seems to have nothing to do with physical activity and fitness, for example a road traffic accident, it is still counted. For this reason, we call the outcome all-cause mortality. Several large studies have repeatedly shown that those engaging in regular physical activity, or those who have increased fitness, have a reduced risk of death from all causes. This reduction is approximately 20% to 35%.

When we examine cardiovascular disease on its own, the reduction in risk increases to about 50%. This means that people who are fit and physically active are reducing their risk of death from cardiovascular disease by 50%. Another way to look at these figures is that people who are physically inactive or very sedentary can have as much as twice the risk of coronary heart disease. In a large study involving several thousand registered female nurses, who were followed for 24 years, those who engaged in less than one hour of physical activity a week experienced 52% increase in all-cause mortality, their cardiovascular-related mortality was doubled, and they had a 29% increase in cancer related mortality, compared with their physically active peers.

Of course, some people have risk factors for cardiovascular disease which are independent of lifestyle, for example, having a family history of heart disease. For these people, being fit and active is still important and can offset their relative risk of mortality. For example, evidence has shown that those who already have risk factors for cardiovascular disease but are fit, may have a lower risk of premature death than those who have no risk factors for cardiovascular disease but are sedentary. Even small improvements in aerobic fitness in those who were previously sedentary can result in significant health benefits. One example of this in the literature was with a group of 9,777 men whose fitness was measured twice, approximately five years apart.

Those who went from being unfit to fit had a 44% reduced mortality risk, when compared to those who remained unfit. In this study, the fitness was measured using an incremental exercise test on a treadmill, whereby each minute the speed or the incline of the treadmill increased. For the group of men who increased their fitness, each additional minute they achieved on the treadmill corresponded to a 7.9% decreased risk of mortality. In other words, exercising for one extra minute in this test corresponded to a significant reduction in risk of mortality. Over all, the evidence is strong and compelling.

It has been proven that increasing aerobics fitness and physical activity levels is effective at reducing the risk of premature death in men and women who are asymptomatic, those with risk factors for cardiovascular disease, and those who have pre-established cardiovascular disease. The evidence also stands for those with disabilities. Similar results have been seen in studies examining the efficacy of physical activity of reducing the risk of developing type 2 diabetes mellitus. A reduction in type 2 diabetes has been reported with an increase in weekly energy expenditure of as little as 500 kilocalories. This is equivalent to approximately 30 minutes walking a day. Exercise is most effective at protecting against type 2 diabetes, in populations who are at high risk of developing it.

Take for example, a patient who is overweight. With modest weight loss, achieved through regular exercise and an appropriate diet, this patient could reduce the risk of developing diabetes by up to 60% within four years. What about cancer? Evidence is mounting in the area of exercise and cancer prevention. It is now clear that being physically active reduces the risk of developing colon and breast cancer. There is also evidence to suggest that physical activity can be protective against other forms of cancer, such as endometrial cancer. Moderate intensity physical activity is sufficient to reduce the risk of cancer and is more protective than light intensity physical activity.

When compared to those who remain inactive, regular physical activity reduces the risk of developing colon cancer by approximately 35%, and breast cancer by approximately 25%.

If we turn our attention to the musculoskeletal system, there are also benefits to be gained. There is strong evidence supporting the benefits of exercise for bone and muscle health. Several randomised, controlled trials have shown increases bone mineral density with physical activity. The activity in question, however, must be such that force is transmitted through the bone. For example, jumping will be more beneficial than swimming. It is weight-bearing and the impact with the ground encourages the maintenance of bone mineral density. Much of the evidence on the health benefits of physical activity have concentrated on aerobic exercise. However, there are also many proven health benefits associated with resistance exercise.

A healthy musculoskeletal system is associated with improved quality of life, psychological well-being, and functional independence. Improvements in muscular fitness, including muscular strength, are particularly relevant for elderly patients who may be frail. Finally, let us consider the potential benefits of exercise on the brain. Evidence is accumulating quickly on the effects of exercise for mental and cognitive health and well-being. We know that exercise and physical activity results in improved mood, reduced anxiety and depression, and is also known to improve cognitive function. This is true both for adults and children. In fact, there is evidence to suggest that regular physical activity can lower the risk of cognitive decline by approximately 20%.

This is especially relevant today in countries where the average age of the population is increasing, and more people than ever are living with dementia and Alzheimer’s disease. In the next step, we’ll be talking about exercise dose for health benefits.