15 to Life – Limited Exercise and Mortality Risk

Abstract & Commentary

By Russell H. Greenfield, MD, Editor

Synopsis: Data from this large observational trial with an average follow-up of over 8 years suggest that even 15 minutes a day of moderate-intensity exercise, such as taking a brisk walk, provides significant health benefits in terms of lowered mortality risks and life extension.

Source: Wen CP, et al. Minimum amount of physical activity for reduced mortality and extended life expectancy: A prospective cohort study. Lancet 2011;378:1244-1253.

Evidence suggesting the health benefits of regular exercise and associated guidelines are commonplace, with authorities calling for a minimum of 30-60 minutes of fitness activity on most days of the week to help support optimal health. There has long been a sense that lesser amounts of physical activity do not offer significant health benefits, but this perspective has largely gone unchallenged. The researchers behind this Taiwanese historical prospective cohort trial assessed the impact of a range of different volumes of physical activity on health.

More than 400,000 people (199,265 men and 216,910 women) who participated in a standardized medical screening program in Taiwan from 1996-2008, and were followed for an average of slightly more than 8 years, formed the basis for this historically prospective cohort study. At enrollment, each participant completed a questionnaire addressing lifestyle information and their personal medical history. Participants were encouraged to return annually for evaluations, at which times the questionnaires would again be completed, but only the answers supplied during the initial visit were used for the purposes of the study.

Individual leisure time physical activity (LTPA) was determined via another questionnaire where subjects were asked to classify the types, intensities, and duration of weekly LTPAs they had performed during the previous month, with examples of types of exercise activities given under four intensity categories: light (walking), moderate (brisk walking), medium-vigorous (jogging), or high-vigorous (running). Metabolic equivalents (METs) were assigned to the activities based on existing guidelines.

The product of intensity (MET) and duration of exercise (h) was calculated for each subject, who were then classified into one of five different activity categories: inactive (< 3.75 MET-h), low (3.75–7.49 MET-h), medium (7.50–16.49 MET-h), high (16.50–25.49 MET-h), or very high (> 25.50 MET-h). The amount of physical activity done at work was also assessed, and on the basis of individual responses participants were classified into one of four different activity levels, ranging from low (mainly sedentary work) to a high level characterized by hard physical labor. Hazard ratios (HR) were calculated to compare mortality risks between individuals in different exercise groups (grouped by volume of exercise) and those in the inactive group.

Results were impressive — compared with individuals in the low-volume activity group, those in the inactive group had a 17% increased all-cause mortality risk (HR 1.17, 95% CI 1.10–1.24) and an 11% increased cancer mortality risk (1.11, 1.01–1.22). Participants in the low-volume activity group, who exercised for an average of 92 minutes per week or about 15 minutes a day, were found to have a 14% reduced risk of all-cause mortality (0.86, 0.81–0.91) and a longer life expectancy compared with subjects in the inactive group by 3 years. Every additional 15 minutes of daily exercise beyond the minimum volume of 15 minutes a day up to 100 minutes daily (after which no additional health benefits accrued) further reduced all-cause mortality by 4% (95% CI 2.5–7.0) and all-cancer mortality by 1% (0.3–4.5). Of note, vigorous-intensity exercise yielded similar or greater health benefits in terms of all-cause mortality reduction when compared with moderate-intensity exercise at similar or greater volumes of activity. The mortality benefits identified were applicable to all age groups and both sexes, even to those with cardiovascular disease risks, and remained consistent after controlling for numerous potential confounding factors.

The study authors conclude that as little as 15 minutes a day of moderate-intensity exercise might provide significant health benefits, even for those at risk for cardiovascular disease, and lessen the risk of death due to cardiovascular disease, cancer, and diabetes.


Prior to the publishing of this paper, the minimum exercise threshold above which mortality benefits reasonably could be expected could only be guessed at. "Guestimates" were usually in the range of 30-60 minutes performed on most days of the week; while reasonable on the surface, many people nonetheless find these fitness goals difficult to meet due to time constraints, health issues, and lack of commitment, among other reasons. In addition, the message that exercise can prevent heart disease and other illnesses is true and somewhat effective, but does not universally motivate people to get moving. But what if the message changed and was made easier to embrace and understand? Imagine if health professionals could honestly report to their patients that lesser but still regular amounts of physical activity, perhaps just 15 minutes a day, and requiring only moderate levels of exertion, could help them live 3 years longer than if they continued to be sedentary — that might be more likely to get a person's attention and light a fire under them. The exercise goal is easily attainable, the association between inactivity and mortality risk easily understandable, and the desire to put off death as long as possible remains pretty popular.

The minimum duration of exercise recommended on the basis of this study's results are 50-75% less than standard fitness guidelines, but additional minutes provide for additional health benefits. The researchers believe their data can be used to motivate people to exercise, and that once they begin they actually might increase the amount of time spent in fitness activities over time. For the relatively fit person who is pinched for time, and in agreement with the findings of a number of other studies, the researchers also found that higher intensity exercise performed for short periods may offer the same or even better health benefits than more moderate fitness activities of longer duration.

It would be great if we could interpret the results of this study as a slam dunk, but it was an observational trial, so cause (a limited amount of exercise) and effect (less risk of death) cannot be solidly defined. The results of observation need to be tested, but in this instance they can be safely promoted even as we await definitive evidence.

Americans have been reported to be more physically active than people living in East Asia where this study was conducted, but there are still too many of our patients who do not exercise regularly. In fact, too many health professionals could be classified as inactive, and we need to be good role models for healthy living. Committing to no less than 15 minutes a day of brisk walking, for example, should be a medical mantra. In a world where so much seems outside our control, how good it is to know, or at least assume reasonably, that such an easily attainable fitness goal may help give us some control over the length of our lives.