Tuesday November 2 2010
Participants reported their own activity levels and cold symptoms
“The best way to stave off a cold this winter is to exercise regularly,” reported The Daily Telegraph. It said a study has found that people who did regular exercise and felt fit cut their risk of a cold by almost half.
This research found that people who said they exercised on five or more days a week reported fewer days with cold symptoms and less severe symptoms than people who did little exercise and said they were unfit. The association between fewer cold symptoms was also seen in people who just perceived themselves to be fit.
There is no doubt that regular exercise has health benefits and it may strengthen the immune system. However, this study was relatively short, lasting only 12 weeks, and relied on the participants reporting their exercise and cold symptoms themselves, which introduces the possibility of error. As such, the findings do not provide particularly robust evidence that exercise reduces the risk of colds. Ideally, longer studies are needed to confirm this association.
Where did the story come from?
The study was carried out by researchers from Appalachian State University and the University of North Carolina, USA. It was funded by Coca Cola and Quercegen Pharmaceuticals, a manufacturer of “plant-based functional ingredients, consumer products, and branded pharmaceuticals”.
The study was published in the peer-reviewed British Journal of Sports Medicine.
Both the Telegraph and the BBC reports were accurate, but did not point out the study’s limitations.
What kind of research was this?
The researchers stated that there is some evidence that moderate exercise can strengthen the immune system, thereby reducing the risk of coughs and colds (also known as upper respiratory tract infections or URTIs).
This cross-sectional study investigated the relationship between the frequency and severity of cold symptoms and self-reported levels of exercise and fitness. On its own, this type of study cannot prove that one thing causes another, but can only demonstrate an association.
What did the research involve?
The researchers initially recruited 1,023 adults aged 18–85 years old using mass advertising in the community. Of these, 1,002 met the study requirements. The researchers recruited both men and women (40% were male and 60% were female) who represented a range of different ages (40% were 18–39 years old, 40% were 40–59 and 20% were 60 or over). The numbers of participants who were classed as normal weight, overweight or obese, according to their BMI, were roughly equal. The recruits were then split into two groups, each of which was followed for 12 weeks. One group was followed from January to April 2008 (winter group) and the other from August to November 2008 (autumn group). During these periods, the researchers monitored the participants’ symptoms and the severity of any URTIs they had.
Two weeks before they started the 12-week monitoring period, the participants completed a survey about their lifestyle habits, either by post or online. This included a food-frequency questionnaire, questions about their perceived fitness levels using a validated 10-point scale, and questions about how often they did aerobic exercise in their leisure time. They were also asked about their stress levels and other factors that might influence their susceptibility to coughs and colds.
The researchers divided the participants into three different groups depending on their perceived fitness levels on the 10-point scale: 1-5 corresponded to low fitness, 6-7 to medium fitness and 8-10 to high fitness. They were also divided into three groups according to their frequency of reported weekly leisure-time aerobic exercise: once a week or less, one to four times a week, or five or more times a week.
During the study period, the researchers used a questionnaire, involving a daily “logging” system, to measure the frequency and severity of cold symptoms. The participants reported to the laboratory at the start and end of the study for height and body mass measurements.
The researchers used standardised methods to analyse the relationship between the participants’ reported exercise and fitness levels and the number of days they reported having cold symptoms and the severity of these symptoms. They combined results from the autumn and winter groups and adjusted the results for seven possible factors that might have affected the outcome (confounders), including age, smoking habits and stress levels.
What were the basic results?
The participants’ reported exercise and fitness levels were associated with the number of days they had cold symptoms and the severity of their symptoms. For example, people who exercised for five or more days a week reported having a cold for about five days (range 3.62–6.35) of the 12-week period, compared to nine days (6.91–10.5) for those who did little or no exercise.
The main findings were:
- People who said they did aerobic exercise five or more times a week had 43% fewer days of cold symptoms than those who said they exercised once a week or less.
- Those in the highest fitness group had 46% fewer days of cold symptoms than those in the lowest fitness group.
- People reporting five or more days of aerobic exercise a week reported their symptoms as being 32% less severe than those who exercised once a week or less.
- The highest fitness group reported symptoms 41% less severe than those in the lowest fitness group.
How did the researchers interpret the results?
According to the researchers, the study shows that people who think they are physically fit or who report a high level of aerobic activity suffer fewer days of cold symptoms and less severe symptoms when they do have colds.
They say that fitness and exercise ranked second only to older age in their effect on the number of days that people had colds, during both autumn and winter. The underlying mechanisms by which aerobic exercise might reduce the risk of colds is still being explored, but the researchers argue that it could act through strengthening the immune system.
This study found a relationship between people’s reported exercise levels and fitness, and the frequency and severity of the cold symptoms they experienced over 12 weeks. Some factors need to be considered when judging its findings:
- The researchers took into account certain confounders that might have affected the relationship observed. However, as they point out, they did not adjust for all possible confounders, including how much people were exposed to cold germs at home (especially from children) or at work. This could have had a significant effect on the frequency with which people caught a cold.
- Secondly, the study relied on people reporting their own exercise and fitness levels and the frequency of their cold symptoms. This introduces the possibility of error, even though validated methods were used to measure cold symptoms. For example, people who perceived themselves as very fit might have been less inclined to report a cold as severe.
- The study only asked people about leisure-time exercise and did not take into account any aerobic exercise they might have done at other times, such as at work.
- Finally, the study was only 12 weeks long and looked at two subgroups during two different seasons, which makes its findings less robust. Had it been longer, or revisited the same groups for two or three years, the results may have been different.
Despite these limitations, regular physical activity has established health benefits, in particular for the heart. Longer studies that take objective measures of the participants’ aerobic abilities would give a better idea of the benefits of exercise for warding off viruses. Until then, there is even more reason to exercise regularly if it could reduce the risk of coughs and colds.