The benefit of leisure-time running in cardiovascular risk factor and overall health control is well established. Runners are less likely to experience high blood pressure, cholesterol problems, diabetes, strokes, certain cancers and even arthritis than the barely- or nonrunners. Mortality reduction with moderate intensity exercise level remains firmly established at around 30-40% at 10-15 years. A usual question for all runners is whether by increasing the distance and the effort you can achieve even higher benefits. There is now sufficient evidence showing that if your primary goal is improved health, there seems to be an upper limit to the desirable mileage.
In a recent study of approximately 55,000 adults who were followed up for an average of 15 years, runners had a 30% lower risk of mortality with a 3-year life expectancy benefit. The 13,000 runners of the study were divided into groups based on their running effort (miles per week, times per week, minutes per week, and speed). Surprisingly there were no significant benefit/mortality differences between any of the running groups. In fact, runners in the low effort group (e.g. <6miles/wk, 1-2 times/wk, <51 min/wk, <6mph) received the full benefits from running with regard to reduction in cardiovascular and all-cause mortality. Based on this and other similar studies the best advice based on the latest science is that for most of us, running for 20 to 30 minutes, or about a mile-and-a-half to three miles, twice per week would appear to be perfect.
On the basis of concerns regarding sudden cardiac death during marathons, recent epidemiologic studies now permit a detailed assessment of such risks with exercise beyond moderate levels of intensity. Overall rates of cardiac arrest and sudden death during or within 24 hours after half and full marathons have been estimated around 0.2 per 100,000 runner-hours, that is very low. The incidence is much higher, but still relatively low, in middle aged (>40) men who most likely have silent coronary heart disease. Low dose pre-race aspirin has been suggested for this runner group as a reasonable strategy to provide heart protection (discuss this with your doctor).