In a large prospective Taiwanese cohort study, prolonged occupational sitting was associated with higher risk of mortality compared with occupational nonsitting. The associated harm of prolonged occupational sitting was attenuated by alternating between sitting and nonsitting, as well as increasing physical activity.

This summary is based on the publication of Gao W, Sanna M, Chen Y, et al. - Occupational Sitting Time, Leisure Physical Activity, and All-Cause and Cardiovascular Disease Mortality. JAMA Netw Open. 2024 Jan 2;7(1):e2350680. doi: 10.1001/jamanetworkopen.2023.50680.

Introduction and methods

Background

In 2020, the WHO guidelines on physical activity recommended to reduce sedentary behaviours because of their negative impact on health [1]. However, the impact of prolonged occupational sitting on health outcomes, as well as the level of leisure-time physical activity (LTPA) needed to attenuate the effects of prolonged occupational sitting, remain unclear.

Aim of the study

The aim of the study was to determine the effects of prolonged sitting at work on all-cause and cardiovascular mortality. Moreover, this study aimed to determine the amount of LTPA and intensity, as measured with personal activity intelligence (PAI) metric, needed to mitigate the health risks associated with prolonged occupational sitting.

Methods

This is a prospective cohort study that enrolled 481.688 participants (≥20 years) without preexisting CVD diagnose who participated between 1996 to 2017 in a membership-based annual to biannual health checkup in Taiwan. During each visit, participants completed a questionnaire on medical history, sitting habits and lifestyle risk factors, and data on metabolic parameters were collected. The mean follow-up period was 12.85 years. Occupational sitting status was divided into 3 groups based on the amount of physical activity at work, namely mostly sitting (n=290.075 [60.2%]), alternating sitting and nonsitting (n=140.210 [29.1%]), and mostly nonsitting (n=51.403 [10.7%]). LTPA status was categorized into 5 groups based on 2 multiple-choice questions. These categories were: inactive (<3.75 metabolic equivalent of task [MET] hours per week or <15 minutes per day), low (i.e., engaged in low LTPA; 3.75-7.49 MET hours per week or 15-29 minutes per day), medium (7.50-16.49 MET hours per week or 30-59 minutes per day), high (16.5-25.49 MET hours per week or 60-89 minutes per day), and very high (≥25.5 MET hours per week or ≥90 minutes per day). Physical activity was assessed with the PAI score which were stratified into 5 groups: inactive, PAI score 1-49, PAI score 50-99, PAI score 100-149, PAI score > 150.

Outcomes

Outcomes were all-cause mortality and cardiovascular mortality.

Main results

• Compared with participants in the mostly nonsitting group, participants in the mostly sitting group had a higher risk of all-cause mortality (HR: 1.16; 95%CI: 1.11-1.20) and cardiovascular mortality (HR: 1.34; 95%CI: 1.22-1.26) after adjusting for sex, age, education, smoking, drinking, and BMI.
• Similar results were observed in all subgroups, which included women, men, <60 years, ≥60 years, smokers, never smokers, BMI ≥25, BMI ≥30, with or without hypertension, and with or without diabetes.
• There was no difference in risk of all-cause mortality between participants in the alternating sitting and nonsitting group compared with participants in the mostly nonsitting group (HR: 1.01; 95%CI: 0.97-1.05).
• Across 4 of the 5 LTPA levels (from low to high), participants in the mostly nonsitting group had a higher risk of all-cause mortality compared with participants in the other 2 groups.
• There was no difference in risk of all-cause mortality at very high LTPA between the 3 groups (HR: 0.65; 95%CI: 0.57-0.72 for mostly sitting; HR: 0.75; 95%CI: 0.66-0.85 for alternating sitting and nonsitting; and HR: 0.75; 95%CI: 0.66-0.85 for mostly nonsitting).
• At PAI categories below 100, participants who were mostly sitting at work had higher adjusted HRs compared with nonsitters (HR of 1 vs. 0.83 for participants who were inactive; HR: 0.88 vs. 0.77 for PAI score 1-49 level; HR of 0.86 vs. 0.74 for PAI score 50-99, respectively).
• On the other hand, the adjusted HRs for participants with higher PAI scores (100-149 and >150) were similar between the mostly sitting and nonsitting groups (HR of 0.77 vs. 0.74 for PAI score 100-149; HR: 0.70 vs. 0.69 for PAI score >150, respectively).

Conclusion

In a large Taiwanese population, prolonged sitting at work was associated with increased risk of all-cause mortality and cardiovascular mortality. The harmful effects of sitting at work were mitigated by alternating between sitting and nonsitting, increasing the amount or intensity of daily physical activity (e.g. 15 to 30 minutes per day of LTPA) or achieving a PAI score ≥100. The authors provide possible interventions for employers to reduce the burden of systemic prolonged occupational sitting, which include facilitating regular breaks, the use of standing desks or activity-permissive workstations, designed areas for LTPA at work and offering company-sponsored group activities. The authors highlight that “[e]mphasizing the associated harms [of prolonged occupational sitting] and suggesting workplace system changes may help society to denormalize this common behavior, similar to the process of denormalizing smoking.”

References

1. World Health Organization. WHO guidelines on physical activity and sedentary behaviour: at a glance. November 25, 2020. Accessed January 31, 2024. https://www.who.int/publications/i/item/9789240014886

Find this article online at JAMA Netw Open