Changing fitness levels changes risk of death

The impact that exercise has on health and death is well known. This paper looks at changes in exercise. It asks what happens to people's risk of death when they change their fitness levels.

Message

Changing fitness levels in middle age can affect the risk of dying. Improving fitness reduces the risk of death; reducing fitness increases it. Just small increases are beneficial, particularly among the unfit.

Reference

G Erikssen et al. Changes in physical fitness and changes in mortality. The Lancet 1998 352: 759-762.

Study

Participants were 1,428 Norwegian men. At the start of the study (1972-1975) they were aged between 40-60 years and healthy, defined as having no evidence of heart disease and no diagnosed hypertension, diabetes mellitus, cancer or other serious disorders. Their physical fitness was assessed on two occasions with an exercise electrocardiographic (ECG) test (using a bicycle) with an interval of seven years. They were also given a clinical examination on both occasions. They were then followed for up to 14 years.

They were divided into quartiles according to their physical fitness (quartile one = least physically fit, quartile four = fittest).

A total of 238 men died, 120 from cardiovascular causes, 75 from cancer and 43 from other causes.

Results

From quartile one to quartile four there was a progressive decrease in risk factors. E.g. men in quartile four smoked less and had the lowest resting heart rate and systolic blood pressure readings.

Compared with the least fit men in quartile one, those in quartiles two, three and four had reduced risks of all-cause mortality of 28%, 52% and 55% (relative risks and 95% confidence intervals for quartile two 0.72 [0.52 to 0.99]; quartile three 0.48 [0.33 to 0.71] and quartile four 0.45 [0.29 to 0.69]). These results were adjusted for several risk factors including age, smoking, systolic blood pressure, body mass index and physical activity. The risks for cardiovascular mortality were very similar to these.

As physical fitness changed, so did the risk of death (see Figure 1). Improvements in fitness lowered the risk of death. Declines in fitness increased it.

Figure 1: This figure shows that death rates (standard mortality ratio) were lower in men who were fitter at the initial survey (Quartile 4 fitter than Quartile 1). It also shows that men who increased their fitness over the two periods (P2/P1) had lower mortality rates than those who did not (Q4 was biggest increase in fitness, Q1 reduced fitness). The message is that improving fitness reduces the risk of dying early whatever the initial level of fitness.

Comment

This study confirms that physical fitness is associated with a lowered risk of death. More importantly, it shows that small improvements in fitness, among the middle-aged, particularly the least fit, substantially reduces the risk of death. For those who increased their physical fitness the most, the change in exercise capacity was only two minutes at bicycle load two (150W). Although this study looked at men, these results are likely to be similar for women.