“An extra walk each day wards off killer heart illnesses,” reports the Daily Express.
The traditional New Year’s Day stroll is good for “blowing the cobwebs away”, and pledging to walk more as a New Year’s Resolution is a great idea, but this headline needs to be taken with a degree of caution.
The news is actually based on the results of a large international study, but it focussed on adults with a high risk of type 2 diabetes and heart disease. For this reason, people at lower risk of these diseases may not get the same benefit.
The researchers found that for this specific group of people, every extra 2,000 steps per day at the start of the study was associated with a 10% lower risk of a “cardiovascular event”, such as a heart attack. A year later, each extra 2,000 steps per day a person took beyond their original amount was associated with an additional 8% difference in the cardiovascular event rate.
The researchers tried hard to adjust their findings for many confounding factors, but because of the study design it remains possible that there were other differences between people who took more or fewer steps per day and that was responsible for the association seen.
Where did the story come from?
The study was carried out by researchers from the NIHR Leicester-Loughborough Diet, Lifestyle, and Physical Activity Biomedical Research Unit and the University of Leicester, and Duke University School of Medicine, US, in collaboration with researchers from other universities and research institutes from around the world. It was funded by Novartis Pharmaceuticals which makes both of the drugs used in the study. The study was published in the peer-reviewed medical journal, The Lancet.
Neither the Express nor the Mail Online made it clear at the start of their stories that the figures they were quoting were from a study of adults at high risk of diabetes and cardiovascular disease. Both papers failed to point out that the findings were associations, and from the results of the current study it cannot be concluded that walking caused the reduction in risk seen.
What kind of research was this?
This was a cohort study which aimed to determine whether the amount of walking a person did and the change in the amount of walking a person does over time are associated with the risk of a cardiovascular event (death due to cardiovascular disease, a non-fatal stroke, or a heart attack) in people at high risk who also have impaired glucose tolerance.
The group of people in this study were taking part in a randomised controlled trial of two drugs: nateglinide and valsartan.
A cohort study is the ideal study design to address this question, and is likely to be the best form of evidence for this question. However, cohort studies cannot show causation. Although the researchers adjusted for a number of potential confounders it could be that there were other differences between people who took more or fewer steps per day and that was responsible for the association seen.
What did the research involve?
The researchers recruited 9,306 people (with an average age of 63) from around the world with impaired glucose tolerance and either:
- existing cardiovascular disease (if aged 50 or older)
- at least one cardiovascular risk factor (if aged 55 or older)
The group of people in this study were taking part in a randomised controlled trial of two drugs: nateglinide and valsartan. People could receive one of either of the two drugs, both drugs, or placebo. Everyone in this trial also participated in a lifestyle modification programme. One of the aims of this programme was to increase physical activity to 150 minutes per week.
The average number of steps that people took per day was assessed at the start of the study and after 12 months using a pedometer.
People were followed-up for an average of six-years for cardiovascular events (death due to cardiovascular disease, a non-fatal stroke, or a heart attack).
The researchers analysed the association between:
- the number of steps taken at the start of the study and risk of a cardiovascular event
- the change in the number of steps taken between the start of the study and 12 months and the risk of a cardiovascular event
The researchers adjusted their analyses for:
- the treatment people were randomised to
- body-mass index (BMI)
- geographical location (continent)
- current smoking status
- coronary heart disease composite (previous heart attack, angina, positive stress test, or coronary revascularisation)and cerebrovascular composite (stroke, transient ischaemic attack)
- other biochemical and clinical factors
What were the basic results?
Each 2,000 steps per day increase or decrease in the number of steps taken per day between baseline and 12 months was associated with an additional 8% lower or higher cardiovascular event rate, respectively.
When the researchers adjusted for change in BMI (which might be expected if people increased or decreased the number of steps they took) the results did not change.
The researchers also found that increasing or decreasing the number of steps taken changed the cardiovascular event rate for everyone, regardless of the number of steps taken at the start of the study (baseline). The results were also not changed by a previous history of cardiovascular disease, sex, age or location.
How did the researchers interpret the results?
The researchers concluded that, “both baseline ambulatory activity and change in ambulatory activity over 12 months were associated independently with the risk of a cardiovascular event in the ensuing five years.
“Specifically, every 2,000 step per day increment in ambulatory activity at baseline (roughly equivalent to 20 min a day of moderately-paced walking activity) was associated with a 10% lower risk of a cardiovascular event.
“Moreover, each 2,000 step per day change from baseline to 12 months was associated with an additional 8% difference in the cardiovascular event rate. This difference was unaffected when further adjusted for change in body-mass index and other potential confounding factors at 12 months. Results were not modified by sex, age, level of baseline activity, or pre-existing cardiovascular disease.”
This study of adults at high risk of type 2 diabetes and heart disease has found that every 2,000 steps they normally took each day was associated with a 10% lower risk of a cardiovascular event. And 12 months later, each extra 2,000 steps per day people did beyond their original number of steps was associated with an additional 8% difference in the cardiovascular event rate.
This large study recruited participants from around the world and the researchers adjusted for a number of potential confounders.
However, the study had a number of limitations, including:
- A large amount of information on the number of steps taken per day was missing, and had to be adjusted for using statistical techniques.
- Although pedometers were used to objectively collect information on the number of steps taken, participants knew they were wearing pedometers and were not blinded to the number of steps taken: it could be that people took more steps than normal when they were wearing a pedometer.
- Cohort studies cannot show causation. Although the researchers adjusted for a number of potential confounders it could be that there were other differences between people who took more or fewer steps per day and these were responsible for the association seen.
- It should also be remembered that all people in this population were at high risk of type 2 diabetes and heart disease. This means that other people may get a different level of benefit from walking.
In any case, this research further emphasises the health benefits of walking. For information and advice see Getting Started: Walking.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Express, 20 December 2013
Daily Mail, 20 December 2013
Links to the science
The Lancet. Published online December 20 2013