Tuesday January 10 2017
When it comes to exercise, every little helps
"Weekend warriors, take a victory lap. People who pack their workouts into one or two sessions a week lower their risk of dying over roughly the next decade nearly as much as people who exercise more often," the Mail Online reports.
New research looked at data from almost 64,000 participants collected as part of health surveys for England and Scotland from 1994 to 2012.
Researchers were particularly interested in what have been termed "weekend warriors": adults who only exercise at the weekend.
They placed participants into four groups based on how much and how often they exercised: inactive, insufficiently active, weekend warriors, and regularly active.
Compared with people who did no physical activity, all active groups – including insufficient activity, regular activity and weekend patterns – saw a reduction in their risk of death from any cause or cardiovascular disease.
But weekend activity had no significant effect on reducing cancer risk, unlike the people in the regularly active groups, and surprisingly the insufficiently active group.
While this large and reliable study is unable to prove cause and effect, the results do seem to confirm the Mail's headline: "It's all good: Any exercise cuts risk of death, study finds".
Read more about how you can fit exercise into your day-to-day regime without having to go to the gym.
Where did the story come from?
The study was carried out by researchers from the University of Leicester, Loughborough University, University College London and the University of Sydney.
Funding was provided by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care–East Midlands, Leicester Clinical Trials Unit, and the NIHR Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit.
It was published in the peer-reviewed journal JAMA Internal Medicine on an open access basis, so you can read it free online.
This study has been widely covered by the UK media, but there were some inaccuracies with the reporting.
BBC News states weekend warriors were found to lower their risk of dying from cancer by 18% compared with the inactive group, but this finding was not statistically significant, so it could have been the result of chance.
The Daily Mirror repeats this error while making the mistake of putting it in its headline: "People who exercise just once or twice a week reduce their risk of dying from cancer by 20%, according to a new study".
What kind of research was this?
This survey aimed to investigate associations between leisure time physical activity patterns and mortality, overall and from specific cardiovascular and cancer causes.
Themes can be identified in this type of study, but it is difficult to have a good level of certainty in the findings.
Surveys are subject to recall bias and cannot prove cause and effect, as unmeasured health and lifestyle factors may be involved in the links.
What did the research involve?
The researchers pooled data from adults aged 40 years or older collected as part of the Health Survey for England and the Scottish Health Survey. Data was collected between 1994 and 2012.
Participants met with trained interviewers and were asked about their level of physical activity using an established questionnaire.
Data was gathered on the participants' physical activity in the four weeks before the interview, and included:
- frequency and duration of participation in domestic physical activity
- frequency, duration and pace of walking (slow, average, brisk or fast)
- participation in sports and exercises (such as cycling, swimming, running) and the associated frequency, duration and perceived intensity
Based on the findings, the patterns of physical activity were defined as:
- inactive – not reporting any moderate- or vigorous-intensity physical activities
- insufficiently active – less than 150 minutes a week of moderate-intensity physical activity and less than 75 minutes a week of vigorous-intensity physical activity
- weekend warrior – at least 150 minutes a week of moderate-intensity physical activity or at least 75 minutes a week of vigorous-intensity physical activity from one or two sessions
- regularly active – at least 150 minutes a week of moderate-intensity physical activity or at least 75 minutes a week of vigorous-intensity physical activity from three or more sessions
In addition to questions on physical activity, the interviewers gathered information on illness, occupation and ethnicity.
Socioeconomic status was established from participants' occupations. The trained interviewers also measured height, weight, and body mass index (BMI).
Causes of death were obtained from death certificates.
What were the basic results?
A total of 63,591 participants were included in the study, with an average age of 58.6 years.
During the follow-up period there were 8,802 deaths from all causes, 2,780 deaths from cardiovascular disease, and 2,526 from cancer.
When compared with inactive participants in the study, the risk of death from any cause was lower for all other activity groups:
- 34% lower for insufficiently active participants (hazard ratio [HR] 0.66, 95% confidence interval [CI], 0.62 to 0.72)
- 30% lower for weekend warriors (HR 0.70, 95% CI, 0.60 to 0.82)
- 35% lower for regularly active participants (HR 0.65, 95% CI, 0.58 to 0.73)
Compared with inactive participants, any level of activity reduced risk of death from cardiovascular disease by around 40%:
- insufficiently active participants (HR 0.60 (95% CI, 0.52 to 0.69)
- weekend warriors (HR 0.60 (95% CI, 0.45 to 0.82)
- regularly active participants (HR 0.59 (95% CI, 0.48 to 0.73)
Compared with the inactive participants, the risk of death from cancer was significantly reduced for insufficiently active (HR 0.83, 95% CI, 0.73 to 0.94) and regularly active participants (HR 0.79, 95% CI, 0.66 to 0.94), but the risk was not significantly lower for weekend warriors (HR 0.82, 95% CI, 0.63 to 1.06).
When comparisons were drawn with the insufficiently active group, no benefit was seen for weekend warriors for all causes of death, death from cardiovascular disease, or death from cancer.
Those who were regularly active saw a reduction in causes of death and death from cancer.
How did the researchers interpret the results?
The researchers concluded that, "Weekend warrior and other leisure time physical activity patterns characterised by one or two sessions per week may be sufficient to reduce all-cause, CVD [cardiovascular disease], and cancer mortality risks regardless of adherence to prevailing physical activity guidelines."
This survey aimed to investigate patterns of physical activity in adults over the age of 40 and the potential impact on their cause of death.
The study found that, compared with those who were not physically active, all active groups saw a reduction in their risk of death from any cause and cardiovascular disease. Being active at the weekend only had no effect on cancer mortality.
However, interpretations around the optimal level of activity are difficult when you note that insufficient activity gave similar mortality reductions as the recommended regular activity.
This study has both strengths and limitations. It is a very large study and data was collected using validated tools and other reliable sources.
The main limitation, however, is it's not able to prove that the amount of exercise taken is responsible for any reductions in risk of death.
There may be a number of unmeasured health, lifestyle and sociodemographic factors at play here.
Also, the weekend warriors only made up a small proportion of the total study population at 3.9%.
Analyses involving smaller numbers of people are less reliable, and this may have been why some of the findings were significant and others not. It's hard to be sure that these are reliable estimates.
The study also only looked at links with cardiovascular and cancer deaths – not at diagnoses of these conditions.
The research team acknowledged a number of other limitations themselves:
- Most of the participants were white, which may reduce the generalisability of the findings to other ethnic groups.
- Physical activity was only assessed at the start of the study, and this may have changed during the study period.
- Self-reported information on physical activity is subject to recall bias – though in this case participants only had to recall the past four weeks.
- Occupational physical activity was not formally assessed, and this may have an effect on the findings.
- Reverse causation is possible in this type of study: that is, participants with an illness that may increase mortality risk are less likely to be active.
Current physical activity guidelines for adults advise taking 150 minutes of moderate activity a week and doing strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms).
Meeting these guidelines could reduce the risk of major illnesses, such as heart disease, stroke, type 2 diabetes and cancer.