The impact of sedentary behavior on the relationship between daily step count and health outcomes

In a recent study published in British Journal of Sports Medicineresearchers examined how sedentary time affects the relationship between daily step count and the risks of all-cause mortality and incident cardiovascular disease (CVD).

study: Do associations of daily steps with mortality and cardiovascular disease incidence differ by levels of sedentary time? A device-based cohort study. Image credit: Wachiwit / Shutterstock.com

The health effects of daily step counting and sedentary time

Daily step counting is associated with reduced mortality and CVD risks, with benefits observed for 4,000–10,000 steps each day. Conversely, long sedentary time correlates with increased risks. Although sedentary time and daily steps affect CVD and mortality risk factors such as obesity and blood pressure, the extent to which sedentary time modifies these associations remains unclear.

Previous research has shown that physical activity can moderate the adverse effects associated with sedentary time; however, specific guidance on daily steps in this context is still lacking. Thus, further research is needed to clarify the influence of sedentary behavior on the health benefits of daily step counting and to refine physical activity guidelines for different levels of sedentary time.

About the research

The current study included participants from the UK Biobank, which is a large prospective cohort consisting of adults aged between 40 and 69 who were enrolled from 2006 to 2010. Participants underwent physical examinations and completed questionnaires. Individuals with prior CVD or cancer, missing data, or events within the first year after accelerometric measurement were excluded.

Physical activity was measured using Axivity AX3 accelerometers that were worn continuously on the wrist for seven days to capture data on daily steps and sedentary time. Valid data required at least three days of observation, including weekend wear and sleep periods, with activity types classified using a validated machine learning scheme.

Mortality and CVD were followed until October 2021, with data linked to national health registries providing outcomes. The study defined CVD excluding hypertension and diseases of the arteries, veins and lymphatic systems. Covariates included demographic, lifestyle, and clinical factors, with additional sensitivity analyzes accounting for potential mediating clinical factors.

Cox proportional hazards and Fine-Gray subdivision models were used to examine the association between daily step count, sedentary behavior and health outcomes. These analyzes determine the optimal and minimum number of daily steps needed to reduce the health risks associated with sedentary time, using rigorous statistical techniques to ensure the accuracy and reliability of the results.

Survey results

A total of 72,174 individuals were included in the study with a mean age of 61.1 years, 57.9% of whom were women. All study participants were followed for an average of 6.9 years, during which 1,633 deaths occurred. For the CVD analysis, 71,441 participants were observed, resulting in 6,190 events.

Participants logged an average of 6,222 steps per day and 10.6 hours of sedentary time while wearing accelerometers for approximately 22.8 hours each day. Those with more sedentary time, who made up 53.8% of the sample, were more likely to be current smokers, have a higher waist circumference, and be on medication for cholesterol and hypertension.

The analysis distinguished between high and low levels of sedentary time of more than and less than 10.5 hours each day, respectively. Marked differences in mortality and cardiovascular disease risks were associated with daily step count in these groups.

A dose-response relationship was observed between steps/day and health outcomes, with the lowest risks of all-cause mortality at 9,000 steps/day for highly sedentary individuals and approximately 10,300 steps/day for those with less sedentary time. For CVD, optimal daily steps were around 9,700 for both groups, with some benefits seen in less sedentary time.

Sensitivity analyzes that adjusted for clinical factors and potential confounders confirmed the robustness of these associations and suggested a complex interaction between physical activity and sedentary behavior in determining health risks.

Additional research has revealed that changing sedentary behavior can moderate the relationship between daily steps and health outcomes. For example, study participants aged 60 and older showed a lower risk of both mortality and CVD for a similar number of steps; however, the benefits are more pronounced for those with less sedentary time.

Conclusions

The optimal daily step range for reducing CVD risk and mortality for the current study was between 9,000 and 10,500 steps, regardless of sedentary behavior. Notably, individuals with high sedentary time had a lower risk for an equivalent number of steps than those with little sedentary time, thus highlighting the importance of increasing daily steps, particularly in sedentary individuals.

The current study highlights the importance of integrating increased physical activity with reduced sedentary time into health strategies using wearable device data for more accurate activity tracking and public health guidance.