“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.
Where did the story come from?
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.
What kind of research was this?
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.
What did the research involve?
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:
- Light (walking)
- Moderate (brisk walking)
- Medium-vigorous (jogging)
- High-vigorous (running)
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:
- Inactive – most participants in this category completed no exercise at all; 54% of the study participants were in this category.
- Low-volume activity – participants in this category completed, on average, light intensity exercise for 90 minutes per week; 22% of the study participants were in this category.
- Medium-volume activity – participants in this category completed, on average, light to moderate-intensity exercise for three hours and 40 minutes per week; 14% of the study participants were in this category.
- High-volume activity – participants in this category completed, on average, moderate-intensity exercise for six hours per week; 5% of the study participants were in this category.
- Very high-volume activity – participants in this category completed, on average, moderate-intensity exercise for eight hours and 40 minutes per week; 5% of study participants were in this category.
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).
What were the basic results?
Analysis of the data showed that:
Risk of death (compared to people in the inactive group) was:
- 14% lower in the low-volume activity group
- 20% lower in the medium-volume activity group
- 29% lower in the high-volume activity group
- 35% lower in the very high-volume activity group
Risk of death from any cancer (compared to people in the inactive group) was:
- 10% lower for people in the low-volume activity group
- 15% lower for people in the medium-volume activity group
- 15% lower for people in the high-volume activity group
- 22% lower for people in the very high-volume activity group
Analysis of life expectancy at age 30 showed that, compared to individuals in the inactive group:
- life expectancy in the low-volume activity group (15 minutes a day) was 2.55 years longer for men, and 3.10 years longer for women
- life expectancy for those who did the recommended daily exercise limits (30 minutes of moderate exercise per day, five days per week) - was 4.21 years longer for men and 3.67 years longer for women
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.
How did the researchers interpret the results?
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:
- The information regarding physical activity was collected at the beginning of the study, and used many years later for data analysis. Exercise habits can change significantly over the course of several years. The assumption that each person maintained their initial activity levels is a weakness of the study. Also, as exercise levels were self-reported via simple multiple-choice questions, some people may have been incorrectly categorised.
- The researchers were very careful to contain their recommendations to East Asian populations, as the average levels of exercise in those populations tend to be lower than in Western populations.
- The body mass index cut-off for obesity in eastern Asian populations, and the number used in this study’s data analysis, was 25 kg/m2. This is lower than the 35 kg/m2 cut-off used in Western societies. It is therefore unclear whether the effects seen in this study apply to other populations.
- Although the data analysis controlled for some known confounders, it is possible that this association is due to other unknown confounders. All-cause mortality is a particularly broad outcome and there are many possible confounding factors that are linked to both exercise and risk of death, such as socioeconomic factors, lifestyle factors and health status. There are also many physical and psychological factors that are interlinked and affect one another. For instance, individuals who were ill may have reduced their activity levels, and healthy individuals probably tend to exercise more. Though this study has made attempts to take into account many known confounders, it is difficult to account for all possible confounders that could affect the results. For this reason, it is not possible to say for certain that exercise levels caused a reduction in risk of death.
- Though the news headlines exercising for ‘health’ it should be pointed out that the research has only looked at all-cause mortality; it has not examined ‘health’ in the context of absence of disease and physical and psychological wellbeing.
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.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 16 August 2011
Daily Mirror, 16 August 2011
Daily Express, 16 August 2011
Links to the science
The Lancet, Early Online Publication, 16 August 2011