Physical activity reduces stress

“A brisk bout of spring cleaning may make you happier,” suggests The Times today. Several newspapers cover new research that claims just 20 minutes a week of any physical activity, such as cleaning or gardening, can have an impact on psychological distress. The Daily Mail reports that the more exercise, the better. It says that people who exercise every day reduce their risk of anxiety and stress levels by more than 40%. BBC News says that light dusting or walking to the bus stop didn’t count, as activities had to last at least 20 minutes at a time and induce breathlessness.

The stories are based on a survey of 20,000 men and women in the UK that found that the more strenuous and frequent the activity, the greater the effect on mental health. There is the possibility that this study is actually showing that those who suffer from stress or anxiety are less likely to take part in physical activity, instead of the other way around. However, the results correspond with similar findings from other studies that show regular physical activity improves mental health.

The authors say that this study is the first to “consider the importance of different activity types in relation to mental health”. The pattern of a reduction in the risk of psychological distress with higher volumes and intensity of physical activity coincides with the findings of other studies and is probably reliable. However, more studies are needed to confirm that just 20 minutes of housework a week is beneficial. In general, people should know that the more exercise they do, the better they will feel, for a variety of reasons.

Where did the story come from?

Dr Mark Hamer and colleagues from the Department of Epidemiology and Public Health, University College London carried out the research. The study was funded by grants from the British Heart Foundation and the National Institute for Health Research. It was published in the British Journal of Sports Medicine , a peer-reviewed medical journal.

What kind of scientific study was this?

This was a cross sectional study based on data from the Scottish Health Survey. This periodic survey occurs every three to five years in households in Scotland, and is aimed at gathering a sample representative of the general population. Different samples of people were used from surveys taken in 1995, 1998 and 2003. A total of 19,842 men and women with an average age of about 45 years were included in the final analysis.

The survey is carried out over two household visits. During the first visit, the participants give their levels of physical activity, and their weight and height are measured. At the second, nurses enquire about their general health and physical activity. They then carry out the General Health Questionnaire (GHQ-12), which measures psychological distress. This scores responses to 12 questions about participants’ general level of happiness, experience of depressive and anxiety symptoms, and sleep disturbance over the last four weeks.

The researchers used statistical methods to model the links between all the measurements, scores and questionnaire responses that they had collected. They related these to the overall risk of psychological distress (given as a GHQ-12 score of four or more).

So that the results were not unduly influenced by other factors, the researchers adjusted for those they knew could or might affect physical activity and psychological distress. These included age, sex, social economic and marital status, body mass index, long-standing illness, smoking and the year in which the survey took place.

What were the results of the study?

The researchers found that 3,200 participants had psychological distress as defined by the GHQ-12. About 32% of the sample performed none or one session of physical activity per week lasting at least 20 minutes, excluding domestic activities. Participants in the higher activity quartiles were more likely to be younger, unmarried, come from a higher socioeconomic group, non smokers, have lower body mass index and lower GHQ-12 scores. They were also less likely to have a long-standing illness.

After adjusting for a number of factors the researchers found that any form of daily physical activity was linked to a lower risk of psychological distress. The more physical activity people engaged in, the less likely they were to indicate psychological distress on their questionnaires. They also showed that the different activities, including domestic tasks (such as housework and gardening), walking and sports, all showed a reduced chance of psychological distress. The strongest effects were observed for those who played sports.

What interpretations did the researchers draw from these results?

The researchers conclude that mental health benefits were observed at a “minimal level of at least 20 minutes a week of any physical activity”. They say that there was a greater risk reduction for activity that was undertaken for longer or at a higher intensity.

What does the NHS Knowledge Service make of this study?

These findings are largely consistent with other studies in the area that have shown the many benefits of physical activity. The authors mention some particular features of this study that limit any interpretations that can be made from the results:

• Given the cross-sectional nature of the data, there is a chance that the results are explained by reverse causality. This means the study might actually be showing that people who suffer from stress or anxiety are less likely to take part in physical activity.
• The researchers attempted to take into account factors, such as illnesses, that might have reduced the participants’ physical activity. They also considered illnesses that might be linked to psychological distress. However, these adjustments may not have fully removed their effects on the results. It is also possible that unmeasured or unknown factors, such as illnesses not considered by the study or medications, may have influenced the results.
• The exact nature of the housework that proved beneficial was not identified.

Despite these limitations, many other studies have also shown the health benefits of physical activity. Some that have suggested that it may reduce the likelihood of depression and cognitive decline. Whether this activity should be in the house, garden or the gym has not been answered by this study.