The study of over 72,000 people, published in the British Journal of Sports Medicine, found every additional step up to around 10,000 steps a day was linked to reduced risk of death (39 percent) and cardiovascular disease (21 percent) regardless of how much remaining time was spent sedentary.
Previous studies have shown an association between greater daily step count and lower levels of death and CVD, and separate studies have linked high levels of sedentary behaviour with increased risks of CVD and death. However, this is the first to objectively measure, via wrist-worn wearables, if daily steps could offset the health risks of high sedentary behaviour.
Lead author and research fellow, Dr Matthew Ahmadi said: "This is by no means a get out of jail card for people who are sedentary for excessive periods of time, however, it does hold an important public health message that all movement matters and that people can and should try to offset the health consequences of unavoidable sedentary time by upping their daily step count."
Senior author Professor Emmanuel Stamatakis, Director of the Mackenzie Wearables Research Hub at the Charles Perkins Centre, said this growing body of physical activity research using device-based measurement provided huge opportunities for public health.
"Step count is a tangible and easily understood measure of physical activity that can help people in the community, and indeed health professionals, accurately monitor physical activity. We hope this evidence will inform the first generation of device-based physical activity and sedentary behaviour guidelines, which should include key recommendations on daily stepping," said Professor Stamatakis.
How was the study conducted?
Researchers used data on 72,174 individuals (average age 61; 58% female) from the UK Biobank study - a major biomedical database - who had worn an accelerometer device on their wrist for seven days to measure their physical activity. The accelerometer data were used to estimate daily step count and time spent sedentary, that is sitting or lying down while awake.
The research team then followed the health trajectory of the participants by linking hospitalisation data and death records.
The median daily step count for participants was 6222 steps/day, and 2200 steps/day (the lowest 5 percent of daily steps among all participants) was taken as the comparator for assessing the impact on death and CVD events of increasing step count.
The median time spent sedentary was 10.6 hours/day, so study participants sedentary for 10.5 hours/day or more were considered to have high sedentary time while those who spent less than 10.5 hours/day sedentary were classified as low sedentary time.
Adjustments were made to eliminate biases, such as excluding participants with poor health, who were underweight or had a health event within two years of follow-up. Researchers also took into account factors such as age, sex, ethnicity, education, smoking status, alcohol consumption, diet and parental history of CVD and cancer.
What did they find?
Over an average 6.9 years follow up, 1633 deaths and 6190 CVD events occurred.
After taking account of other potential influences, the authors calculated that the optimal number of steps per day to counteract high sedentary time was between 9000 to 10000 steps/day, which lowered mortality risk by 39 percent and incident CVD risk by 21 percent.
In both cases, 50 percent of the benefit was achieved at between 4000 and 4500 steps a day.
Study limitations
This is an observational study so can't establish direct cause and effect. And although the large sample size and long follow-up allowed the risk of bias to be reduced, the authors acknowledge the possibility that other unmeasured factors could affect results. As steps and sedentary time were obtained in a single time point, this could also lead to bias, they add.
Nevertheless, they conclude, "Any amount of daily steps above the referent 2200 steps/day was associated with lower mortality and incident CVD risk, for low and high sedentary time. Accruing between 9000 and 10,000 steps a day optimally lowered the risk of mortality and incident CVD among highly sedentary participants."
Declaration: This study is funded by an Australian National Health and Medical Research Council (NHMRC) Investigator Grant and National Heart Foundation Fellowship.
