“15-minute of daily exercise is the ‘bare minimum for health’,” reported BBC News. It added that “just 15 minutes of exercise a day can boost life expectancy by three years, and cut death risk by 14%”.
This news story is based on research investigating the benefits of different levels of physical activity. About 400,000 adults in Taiwan were asked about their exercise habits, then followed for about eight years. Compared to being inactive, doing low-volume activity (15 minutes a day) was calculated to reduce risk of all-cause mortality by 14%, and each additional 15 minutes of exercise above this reduced mortality by a further 4%.
This is a large study, but it also has some limitations, including the fact that exercise levels were only assessed once at the study’s beginning, and these measurements were dependent on the participants’ own responses. Also, the study only looked at deaths from any cause, and not the health and wellbeing of the participants.
This finding that small amounts of exercise may be of some benefit does not change current UK exercise guidelines, which recommend at least 150mins (2 ½ hours) of moderate-intensity activity a week. It does, however, add to the considerable amount of evidence that not only is exercise good for your health, but the more you get, the better. See our Live Well fitness section for detailed advice on how to get fit.
The study was carried out by researchers from the National Research Institutes of Taiwan, the China Medical University Hospital, the National Taiwan Sport University, the University of Washington in the US, the Chung Shan Medical University and Hospital in Taiwan, MJ Health Management Institution in Taiwan, the University of Texas School of Public Health, and the MD Anderson Cancer Centre in the US. The research was funded by the Taiwan Department of Health and the National Health Research Institutes.
The study was published in the peer-reviewed medical journal The Lancet .
Generally, the study was reported accurately by the media. The BBC’s headline is more accurate in saying that 15 minutes is the ‘bare minimum for health’. The Express headline (‘Live longer with just 15 minutes’ exercise’) makes it seem that this is all the level of exercise that is required, which is not the conclusion made by this study. In addition, it is important to note that the research has only looked at the effect of exercise on all-cause mortality (death from any cause); it has not examined ‘health’ in the context of absence of disease and physical and psychological wellbeing.
Many newspaper reports also mention a related study about the impact of TV watching on lifespan. This appraisal only examines the former study.
This was a prospective cohort study looking at the weekly exercise habits and death risk of about 400,000 adults in Taiwan. The study aimed to assess the health benefits of different levels of exercise, and to determine whether or not less exercise than the common standard of 150 minutes per week (as recommended by WHO and the US and UK governments) is associated with a lower risk of death and a longer life expectancy.
A cohort study can examine the association between two characteristics, but cannot prove causation. Particularly in a study such as this, which examined the broad outcome of all-cause mortality, there could be many possible confounding factors that are linked to both exercise and risk of death - for example, socioeconomic factors, lifestyle factors and health status - which could include many levels of physical or psychological comorbidity. Although these researchers tried to take into account many known confounders during their analysis, it is difficult to account for all possible confounders that could affect the results.
The researchers recruited 416,175 adults to participate in the study. Each person filled out a questionnaire regarding their medical history and lifestyle habits, including the intensity and duration of any exercise they did. This was assessed through three multiple-choice questions. First, participants were asked to classify the types and intensity of weekly exercise, and they were put into one of four categories according to their response:
The participants were then asked how long they had spent on these activities over the past month, and how much physical activity they got through their work. Each person was assigned to one of five activity volume categories, which was a combination of intensity and duration of activity:
The participants were then followed-up for an average of eight years, after which time the researchers searched the National Death registry and National Cancer Registry to determine which of the cohort members had died during that time, and which had died specifically of cancer. This information was then used to compare the risk of death in each of the activity groups to the risk of death in the inactive group.
The researchers controlled for potential confounding factors, including age, sex, education level, amount of physical labour at work, smoking status, alcohol consumption, blood pressure, diabetes, history of cancer, and body mass index (as a measure of obesity).
Analysis of the data showed that:
Risk of death (compared to people in the inactive group) was:
Risk of death from any cancer (compared to people in the inactive group) was:
Analysis of life expectancy at age 30 showed that, compared to individuals in the inactive group:
The researchers found that every additional 15 minutes of daily exercise (beyond the 15 minutes per day of the low-volume group) resulted in a further 4% reduction in risk of death from any cause, and a 1% lower risk of death from cancer. This association held up to 100 minutes of exercise per day, at which point the effect levelled out, and no additional benefit was seen.
The relationship between daily physical activity duration and reduced risk of death remained even when potential confounders were taken into account, including age, sex, smoking or drinking status, obesity, and health status.
The researchers concluded that 15 minutes of moderate-intensity exercise each day, or 90 minutes per week, may be beneficial for lifespan. This benefit seems to hold regardless of age, sex or risk of heart disease. They say that their findings have important implications for clinical practice, as it appears that people can benefit from lower levels of exercise than currently recommended.
This large cohort study from Taiwan found that compared to being inactive, doing low-volume activity (15 minutes a day) reduced the risk of all-cause mortality by 14%. Each additional 15 minutes of exercise above this reduced mortality by a further 4%.
The most recent UK guidelines published earlier this year recommend at least 150mins (2 ½ hours) of moderate-intensity activity a week for adults aged 19-64. This research does not change these recommendations. Most people should still aim to meet this amount. For detailed advice on how to achieve your recommended exercise levels, visit the fitness section in Live Well.
The findings of this study may be unsurprising in showing that even a little exercise is better than none at all. As the researchers say, these findings are helpful in showing that for, people who cannot achieve recommended levels of exercise, there may be a health benefit below that level. Additionally, for individuals trying to regain fitness levels after periods of inactivity, smaller increments of exercise may be easier to achieve and still confer some benefit. Starting at 15 minutes a day and working up to the recommended levels of exercise could be a useful way to incorporate exercise into a daily routine. The authors of the current research say that the “identification of a minimum amount of exercise, sufficient to reduce the risk of death, is desirable because a small amount of exercise can be easier to achieve”.
When interpreting these findings, several aspects of the study should be considered:
Despite the limitations of a cohort study to assess causality, this was a large cohort study, which examined the links between activity levels and health benefit. The results may be useful in terms of motivating currently inactive individuals to start an exercise routine, and slowly build up to the recommended activity levels.
In the end, the repeated message of research and guidelines is that when it comes to exercise, some is better than none, and more is better than some.