Tuesday May 4 2010
It is not clear if mood would have improved with non-green exercise
“Five minutes exercising in the countryside boosts mental health,” reported The Daily Telegraph. It said a study has found that “exercising in wilderness areas or near water tended to have the biggest impact on mental state” and that “the greatest health changes were seen in the young and the mentally-ill”.
This news report is based on research that pooled the results of 10 studies from the University of Essex on the effect of outdoor exercise in green environments on self-esteem and mood. It has a number of limitations, including the fact that all the studies came from the same institution, and more robust results may have been achieved by systematically searching for and pooling all research addressing the same question.
Also, the pooled studies did not include control groups, so it is not clear whether these improvements would have occurred naturally over time, or if gym exercise or other leisure activities would have similar results.
Physical activity is known to be beneficial for health, including mental health. Ideally, individuals should take part in physical activity that they enjoy, which may include outdoor exercise.
Where did the story come from?
The research was carried out by Dr Jo Barton and Professor Jules Pretty from the University of Essex. No sources of funding were reported within the journal article. The study was published in the journal Environmental Science and Technology.
The Daily Mail, Daily Telegraph, Daily Express and BBC News reported this study. Although these news sources describe the results of the research accurately, they do not point out its limitations. The Daily Mail’s headline “Forget the gym! An open-air workout can work wonders for the mind” may imply that this study found that an open-air workout was better for mental health than a gym workout, which was not the case.
What kind of research was this?
This study is a meta-analysis, pooling the results from 10 previous UK studies on the effect of ‘green exercise’ on mood and self-esteem. The researchers defined green exercise as activity in the presence of nature. The study aimed to determine the optimal dose of green exercise for improving these outcomes.
Pooling the results of several studies that address the same question can give a more reliable result than the individual studies themselves. These studies’ designs and methods must be similar enough for it to make sense to pool their results. However, it is also important to look at how the studies were chosen for inclusion in the meta-analysis.
In this case, only studies conducted by the University of Essex were included, because these studies all used the same scales to measure the outcome of green exercise. This means that the meta-analysis will be representative of the results obtained in these trials, but may not be representative of the findings of other research institutions.
What did the research involve?
The meta-analysis included 10 studies in a total of 1,252 volunteers, carried out by the University of Essex over the past six years. The results of these studies were pooled using standard methods. The data was analysed to find the optimal “dose” of green exercise (intensity and length) for producing the greatest improvements in mood and self-esteem. The researchers also looked at how the results were affected by the location of the exercise, and an individual’s age, gender, and whether they had existing mental health problems.
Volunteers included people already choosing to do green exercise (such as people in country parks, at national trust sites, urban flower shows or care farms), members of a local mental health association (Mind), allotment holders, young offenders and students. Exercise activities included walking, cycling, fishing, boating or sailing, horse-riding, farming activities and gardening.
Environments in which these activities took place included urban parks, countryside, farmland, forest and woodland, waterside areas and wild habitats. The 10 studies all looked at participants’ mood and self-esteem immediately before and after green exercise. They also all used the same commonly used measurement scales to assess self-esteem and mood.
The analyses looked at different durations of exercise: 5 minutes, 10-60 minutes, half day, or whole day. Different exercise intensities were also examined. These were grouped as low (less than three metabolic equivalents [METs, a standard measure of exercise intensity], moderate (three to six METs) and vigorous (more than six METs).
What were the basic results?
The meta-analysis indicated that green exercise was associated with statistically significant improvements in self-esteem and mood, with slightly larger improvements seen in mood than self-esteem. As the individual studies had found considerably different results for both of these outcomes, the researchers investigated this finding further. They carried out an analysis of the different groups and exercise types to see how the effect varied. For example, they carried out separate analyses of the type of green space, exercise duration or exercise intensity.
The researchers found that these improvements were greatest with five minutes of green exercise, with smaller benefits seen for longer exposures (from 10 minutes to a whole day). Light-intensity activity had the greatest effect on self-esteem; light activity and vigorous activity had similar effects on mood, with less effect seen for moderate activity.
All of the green environments had a positive effect on self-esteem and mood. The greatest effect was seen in environments that featured water, but the researchers say it was not clear whether its difference from other green environments was statistically significant.
Green exercise had a similar effect on self-esteem and mood for both men and women. People with self-reported mental health problems showed greater improvements in self-esteem with green exercise than those without such problems. But they showed no difference in improvements in mood. The improvements in self-esteem were greatest for people under 30, while the improvements in mood were greatest for those aged 31 to 70 years old. It was not clear whether the differences between the different age groups would be statistically significant.
How did the researchers interpret the results?
The researchers conclude, “this study confirms that the environment provides an important health service”.
There are a number of limitations to this study:
- The study only included and pooled research from one research institution. There may be research from other institutions with differing results. The ideal way to summarise existing data on the effects of green exercise would be to conduct a systematic review, with searches carried out to identify all relevant studies.
- The studies included were ‘before and after’ studies, and did not include control groups (for example, individuals doing no exercise and staying indoors, or doing non-green exercise). This means that it is not possible to say whether the improvements seen in mood or self-esteem would have occurred naturally over time without green exercise, or whether similar improvements would be seen by being in the green environment without exercising, or with non-green exercise.
- The participants were mainly people who were either choosing to do green exercise activities, or visiting and participating in outdoor events. Their response to green exercise may be different to people who do not usually choose to engage in these activities.
- The number of participants included was relatively small, particularly when they were broken down into different subgroups (for example, only 105 individuals had mental health problems). This may reduce the reliability of results. There may also be differences between the groups other than the factors of interest that account for some of the differences seen.
- It was not clear whether the participants in all of the studies were asked about their mental health, or just in some studies. Mental health problems were self-reported, meaning that some people with such problems may have been missed, and those reporting problems may not have all been formally diagnosed.
- The studies measured mood and self-esteem immediately before and after exercise. It cannot say what the long-term effects on these outcomes would be, nor the effects on other health outcomes, such as mental illness.
Although this research suggests that people can feel an improvement in mood and self-esteem with green exercise, it cannot prove that this improvement would not have occurred naturally over time, or tell us how the improvements seen compare to what would be seen with other forms of exercise or leisure activity. The idea of green exercise is attractive to many people, but a better quantification of the benefits will be needed to support its role, which these researchers are promoting as a ‘health service’.