Wednesday November 11 2009
“People who walk slowly are three times more likely to die from cardiovascular disease than those who go at a brisk pace,” according to the Daily Express.
The news is based on a study that assessed the walking speeds of over 3,000 elderly people and compared them to death records for several years after. Researchers, who took into account any existing heart disease or other illnesses the participants had, found that 6.9% of the slowest walkers died of heart disease compared to just 1.9% of the fastest walkers. There are a number of possible explanations for the association between slow walking and heart disease. For example, people who already have undetected mild heart failure or early narrowing of the arteries in the legs could be slower walkers because of this.
While the reasons behind the relationship between slow walking and heart disease are open to debate, this study suggests that a simple measure of fitness may be suitable for assessing the health of people aged 65 and over. The benefits of physical activity to the heart are well known, and this research adds more weight to the principle that physical activity reduces rates of death.
Where did the story come from?
This research was conducted by Dr Julien Dumurgier and colleagues from the INSERM research foundation in Paris and other organisations in France. The study was supported by grants from INSERM, the Victor Segalen-Bordeaux II University and the Sanofi-Synthélabo Company. The study was published in the peer-reviewed British Medical Journal.
The Daily Telegraph also covered this story, reporting that the people who were judged to be slow walkers were also 44% more likely to die from any cause. The Daily Express pointed out that, in this study, the faster walkers did not have a lower risk of dying from cancer, despite evidence from previous research that exercise may reduce the risk of developing certain types of tumour.
What kind of research was this?
This was a prospective cohort study which explored the relationship between slow walking speed and risk of death in older people. The researchers followed 3,208 French men and women aged 65 or older. Subjects were all people living in the community and were followed for an average of 5.1 years from 1999–2001.
The researchers explain that it is already known that lower walking speed has been associated with an increase in rates of death from all causes, but it is currently unknown whether this overall increase in mortality is due to specific causes of death. The researchers conducted a cohort study, which is the best design for looking at these associations. Other study models that randomise participants into fast- and slow-walking groups may not be possible.
What did the research involve?
The researchers had data from the 3C study, an ongoing study that recruited participants from the electoral rolls in three French cities (Bordeaux, Dijon and Montpellier). In total, 37% of the people who were approached by letter and phone agreed to participate. This walking study only used the data from Dijon, which included details of the participants’ motor function.
A wide range of tests and questionnaires was given by trained psychologists. As they aimed to use the data for several future analyses, they asked the participants about their education, history of coronary artery disease, peripheral artery disease, stroke, Parkinson’s disease and recent hip fracture (in the two preceding years). Blood pressure was measured and blood tests were used to diagnose diabetes or high blood cholesterol. Smoking status was classified as current, past or never. Weight and height were measured and used to calculate body mass index (BMI). Physical activity was also assessed through the participants’ self-reporting of their daily walking and athletic activities.
For the walking test, participants were first asked to walk at their usual speed and were then invited to walk down the corridor as fast as possible without running. They started walking three metres before the start line so that their acceleration phase did not count towards their walking speed. The researchers excluded data on participants who, at the start of the study, had been diagnosed with conditions that are strongly associated with decreased walking speed (for example, dementia, hip fracture in the previous two years and disabling stroke).
The researchers’ exclusion criteria mean that the study may still have included people with undiagnosed conditions or conditions not yet severe enough to be noticed. These may affect walking speed and could be responsible for “reverse causality”, a type of bias where the outcome affects the exposure. For example, a heart problem may have led to a slow walking speed, rather than the other way around.
Walkers were divided by sex, as women were likely to have slower walking speeds than men, and each sex was split into three speed ranges:
- Men with a maximum speed of 1.50 m/s (metres per second) or less.
- Men between 1.51 and 1.84 m/s.
- Men with a maximum speed of 1.85 m/s or more.
- Women with a maximum speed of 1.35 m/s or less.
- Women between 1.36 and 1.50 m/s.
- Women with a maximum speed of more than 1.50 m/s.
After the initial tests, the researchers followed participants for around five years, recording information on deaths, from any cause and according to the main causes of death. They related these to the walking speed at the beginning of the study (measured as a maximum speed over six metres), which was adjusted for several potential confounding factors, including age, sex, median age, median body mass index (BMI), education, mental state and level of physical activity.
The links shown in the ‘all causes of deaths’ and cardiovascular disease groups remained significant after all the adjustments. This suggests that the association with walking was strongest for these causes of death (and not so strong for cancer or other causes).
What were the basic results?
The researchers say that over the follow-up period, 209 participants died: 99 from cancer, 59 from cardiovascular disease and 51 from other causes.
The unadjusted figures showed that participants in the lowest third of walking speed had an increased risk of death from any cause compared with those in the upper two-thirds (hazard ratio [HR] 1.44, 95% confidence interval [CI] 1.03 to 1.99).
After the researchers had adjusted for nineteen separate factors, their analyses for specific causes of death showed that participants with low walking speed had about a threefold increased risk of cardiovascular death (HR 2.92, 95% CI 1.46 to 5.84) compared with participants who walked faster. After adjustment, there was no relationship between walking speed and cancer mortality (HR 1.03, 95% CI 0.65 to 1.70).
How did the researchers interpret the results?
The researchers say that “slow walking speed in older people is strongly associated with an increased risk of cardiovascular mortality.”
This relatively large, well-conducted study of older people suggests that the main benefit of physical activity in the form of fast walking is to protect against heart disease and not cancer. This association was shown in a population of healthy older adults and reinforces the message that physical activity and walking have major lifetime benefits.
However, the study cannot completely rule out the possibility that heart disease or another disease, common in this age group, was somehow related to slower walking at the start of the study. It is possible that some other factor caused the association seen by reducing walking speed and contributing to heart disease risk. Equally, undiagnosed heart problems might be the cause of slower walking speed, rather than the other way around.
Although the exact cause-and-effect relationship seen in this study is unclear, the strong link between mobility and mortality suggests that a simple walking-speed test may play a role in the assessment of fitness in older people. Other research has clearly shown that the heart benefits from physical activity, and this should be promoted.