Abstract and Introduction
Abstract
Aims While excessive sitting time is related adversely to cardio-metabolic health, it is unknown whether standing is a suitable replacement activity or whether ambulatory movement is required. Using isotemporal substitution analyses, we modelled cross-sectional associations with cardio-metabolic risk biomarkers of reallocating time (2 h/day) from sitting to standing or to stepping.
Methods and results A subsample of participants from the 2011/12 Australian Diabetes, Obesity, and Lifestyle Study wore the posture-based activPAL3 monitor [36–80 years (mean 57.9, SD 9.9 years); 57% women; n = 698 with data]. Associations of activPAL3-derived mean daily time sitting/lying (sitting), standing and stepping with body mass index (BMI), waist circumference, blood pressure, HbA1c, fasting glucose and lipids (high-density lipoprotein-, HDL, and low-density lipoprotein-cholesterol, total/HDL-cholesterol ratio, and triglycerides), and 2-h plasma glucose were examined. Adjusted for relevant confounders, sitting-to-standing reallocations were only significantly (P < 0.05) associated with approximately 2% lower fasting plasma glucose, 11% lower triglycerides, 6% lower total/HDL-cholesterol ratio, and 0.06 mmol/L higher HDL-cholesterol per 2 h/day. Sitting-to-stepping reallocations were only significantly associated with approximately 11% lower BMI, 7.5 cm lower waist circumference, 11% lower 2-h plasma glucose, 14% lower triglycerides, and 0.10 mmol/L higher HDL-cholesterol per 2 h/day, while standing-to-stepping reallocations were only significantly associated with ˜10% lower BMI, 7 cm lower waist circumference, and 11% lower 2-h plasma glucose.
Conclusion Findings suggested that sitting-reduction strategies targeting increased standing, stepping, or both, may benefit cardio-metabolic health. Standing is a simple alternative to sitting, and requires further examination in prospective and intervention studies.
Introduction
High levels of sedentary time—or, too much sitting—have been linked detrimentally with cardiovascular disease, diabetes, and premature mortality. In modern society, adults are highly sedentary, with the average self-reported sitting time ranging from 3.2 to 6.8 h/day across 32 European countries and objective measures indicating 55–69% of adults' waking hours are spent sedentary. Accordingly, broadly stated guidelines on reducing sitting time have emerged. For these to become more specific guides to action, it is important to understand the relative benefits of the common daily activities (standing and stepping) that could replace sitting. The cardio-metabolic health benefits of ambulatory activity are well established. However, the potential benefits (or harms) of standing, a non-ambulatory alternative to sitting, are less well understood. Experimental studies have shown acute benefits of standing for postprandial glucose responses, but there is little evidence regarding non-acute relationships of directly measured standing with glucose metabolism or other cardio-metabolic risk biomarkers. Moreover, existing evidence seldom considers time displacement—that reduced time spent in one activity (e.g. sitting) inevitably increases time spent in other activities (e.g. standing). The potential cardio-metabolic impact of sitting reductions should include both the impact of reducing sitting time and of increasing time spent in non-sitting activities (i.e. standing or stepping).
Isotemporal substitution addresses such time displacements, estimating associations observed when cross-sectionally reallocating time from one activity to another, keeping total time and time in other activities fixed. Studies measuring activity with hip-worn accelerometers suggest the benefits of reducing sedentary time on cardio-metabolic biomarkers likely vary depending on what displaces sedentary time. Stronger associations are observed when time (e.g. 1 h) is reallocated from sedentary to moderate- to vigorous-intensity activity than to light-intensity activity. However, isotemporal substitution has not yet been used to examine the potential health-related impacts of reallocating time from sitting to standing. This is necessary given recent findings show large shifts between these non-ambulatory activities are feasible and acceptable but have an unknown cardio-metabolic impact.
Using data collected from postural sensors, we examined cross-sectional associations of sitting, standing, and stepping with cardio-metabolic risk biomarkers in a broad sample of Australian adults. Associations were estimated considering time displacement (isotemporal substitution).