Tuesday April 7 2015
Jogging and cycling were linked to a reduced risk of premature death
"Short bursts of vigorous exercise helps prevent early death," The Independent reports after an Australian study found vigorous exercise, such as jogging, reduced the risk of premature death.
The study involved adults aged 45 to 75 years old followed up over 6.5 years. Those who did more vigorous activity (as part of their general total moderate to vigorous activity levels) were less likely to die during follow-up than those who did no vigorous activity.
This large study was well designed, and the researchers also tried to take factors into account that they knew could influence the results (confounders).
But, as with all studies, there are some limitations – for example, the researchers only asked about physical activity once and this may have changed over time.
These results also bear out the proven benefits of exercise, regardless of how much of it is vigorous, and supports current recommendations for the amount of physical activity people should do.
While doing some vigorous activity may bring some benefits, it is important that people set themselves realistic targets they can safely achieve.
Where did the story come from?
The study was carried out by researchers from James Cook University and other universities in Australia. It was funded by the Heart Foundation of Australia.
The study was published in the peer-reviewed medical journal JAMA Internal Medicine.
The coverage in the papers is variable. While all the papers are right in saying that vigorous exercise may be beneficial, there is some misreporting. The Daily Telegraph's headline says that, "Swimming, gardening or golf 'not enough to prevent early death'," which is not true.
Gentle swimming and vigorous gardening both fell under "moderate activity", and even those who just did moderate activity had a lower risk of death than those who did no moderate to vigorous activity at all.
The Telegraph also talks about the effects on heart disease and diabetes, but these outcomes were not assessed by this study.
The Daily Express helpfully includes a quote noting that, "There is no question that some exercise is better than nothing. But the more intensive the activity, the less likely people will come back to it, so the question is how do we get people to do some – and then those who do some to do a bit more?"
However, at the end of the story, they then include a video of "chubby guy dancing in Speedos to holiday exercise class" for people's amusement, which is not likely to encourage people to take up exercise.
The Independent refers to "short bursts" of vigorous exercise being beneficial, but the study itself did not assess length of the bursts.
The paper does include a note of caution from one study author, however, who said that, "For those with medical conditions, for older people in general and for those who have never done any vigorous exercise before, it's always important to talk to a doctor first."
What kind of research was this?
This was a prospective cohort study assessing whether achieving more moderate to vigorous activity through vigorous activity specifically was associated with a reduced risk of death during follow-up.
While we know that physical activity is associated with longer life, it is not clear whether vigorous activity is better than moderate activity.
While a recent systematic review suggested that vigorous activity may reduce the risk of death more than moderate activity, some of the studies included did not take overall activity into account.
This means these studies were not able to rule out that some of the effect of vigorous exercise was because people who did more vigorous activity tended to do more physical activity overall.
The current study wanted to avoid this problem. A prospective cohort study is the best way to assess this question. It's unlikely to be feasible to carry out a randomised controlled trial to successfully answer this question, as it's difficult to get people to agree to stick to a specific exercise pattern for a long time.
But the main limitation of a cohort study is that factors other than the factor of interest (such as overall activity, in this case) could potentially influence the results, so the researchers need to take these into account in their analyses.
What did the research involve?
The researchers enrolled adults aged 45 and over from New South Wales. At the start of the study, participants were asked how much physical activity they did and how intense this activity was.
They were then followed up over about 6.5 years, and the researchers identified who died in this period.
The researchers then analysed whether the proportion of the total moderate to vigorous physical activity (MVPA) a person did that was vigorous was associated with their risk of death.
The participants were enrolled as part of the 45 and Up study in 2006-09. Potential participants were selected at random from the Australian national medical insurance (Medicare) database, which includes all citizens and permanent residents of the country.
This study did not include people aged over 75, as it was mainly interested in earlier preventable deaths.
Participants filled out a questionnaire at the start of the study on their MVPA in the past week. They were asked how much of this activity was:
- vigorous – anything that "made you breathe harder or puff and pant", such as jogging, cycling, aerobics or competitive tennis, but not household chores or gardening
- moderate – gentle swimming, social tennis, vigorous gardening or housework
Participants also reported how much walking they did, and this was included in their total MVPA.
Those who died between the start of the study and June 2014 were identified through the New South Wales Registry of Births, Deaths, and Marriages.
The main analyses in this study included 204,542 people who reported doing at least some MVPA. The researchers took factors that could affect the results (potential confounders) into account, including:
- total MVPA
- educational level
- marital status
- area of residence (urban or rural)
- body mass index (BMI)
- physical function (whether the person had any physical limitations)
- smoking status
- alcohol consumption
- fruit and vegetable consumption
What were the basic results?
During the study, 7,435 of the 217,755 participants died:
- 8.3% of those who did no MVPA
- 4.8% of those who did 10 to 149 minutes of MVPA a week
- 3.2% of those who did 150 to 299 minutes of MVPA a week
- 2.6% of those who did 300 minutes or more or MVPA a week
After taking potential confounders into account, this meant that compared with those who did no MVPA, the risk of death during the 6.5 years of follow-up was:
- 34% lower in those who did 10 to 149 minutes of MVPA a week (hazard ratio [HR] 0.66, 95% confidence interval [CI] 0.61 to 0.71)
- 47% lower in those who did 150 to 299 minutes of MVPA a week (HR 0.53, 95% CI 0.48 to 0.57)
- 54% lower in those who did 300 minutes or more or MVPA a week (HR 0.46, 95% CI 0.43 to 0.49)
Among those who did at least some MVPA, doing more of that activity as vigorous activity was associated with a reduced risk of death during follow-up:
- 3.8% of those who did no vigorous activity died
- 2.4% of those who did vigorous activity that accounted for less than 30% of their total MVPA died – a 9% reduction relative to those who did none (HR 0.91, 95% CI 0.84 to 0.98)
- 2.1% of those who did vigorous activity that accounted for 30% or more of their total MVPA died – a 13% reduction relative to those who did none (HR 0.87, 95% CI 0.81 to 0.93)
The researchers found similar results when they looked at people with different BMIs, people who did different amounts of MVPA, and in people with or without cardiovascular disease or diabetes.
How did the researchers interpret the results?
The researchers concluded there was an "inverse dose-response relationship" between the proportion of MVPA done as vigorous activity and the risk of death during follow-up.
They say this suggests that vigorous activity "should be endorsed in clinical and public health activity guidelines to maximise the population benefits of physical activity".
This large study suggests that in middle to older age, doing more of your total moderate to vigorous activity as vigorous activity could help to reduce your risk of death.
This study's size is one of its strengths, with more than 200,000 people taking part. The fact that information on activity was collected at the start of the study, rather than asking people to recollect what they did in the past, is also beneficial.
The researchers also tried to take factors into account that they knew could influence their results, including cardiovascular medical conditions such as coronary heart disease, or other conditions that reduced people's ability to participate in physical activity, such as type 2 diabetes.
But, as with all studies, there are some limitations:
- The researchers only asked about physical activity once, and people's activities may have been different before or after the week that was assessed.
- The study only included those aged 45 to 75, and results may not apply to older individuals.
- All lifestyle measures were reported by the participants themselves, and there may be some inaccuracies – the authors state people tend to be better at reporting vigorous activity than other types of activity.
- The results may still be influenced by confounders the authors did not measure – for example, only fruit and vegetable intake was assessed as a sign of a healthy diet, but other dietary aspects could have had an effect.
While the results suggest that doing more vigorous activity is beneficial, there are some points to think about. For example, the people who were doing more vigorous activity may also have done more vigorous activity in their younger years, and it may be that this consistency is the important factor.
The study also did not directly compare just moderate activity with vigorous activity. Further research is likely to assess these and other questions.
Importantly, the results highlight the beneficial effect of doing some moderate to vigorous activity, regardless of how much of it is vigorous. This supports current recommendations for exercise.
While doing some vigorous activity may add some benefit, it is important that people set themselves realistic targets they can safely achieve.
If it has been a while since you last exercised, the NHS Choices Couch to 5K running programme is one way to safely raise your fitness levels.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.