By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
SYNOPSIS: The authors of this meta-analysis explored the effects of interrupting sitting with either light-intensity walking or standing. They found light-intensity walking was associated with the most significant effect on several markers of cardiometabolic health.
SOURCE: Buffey AJ, Herring MP, Langley CK, et al. The acute effects of interrupting prolonged sitting time in adults with standing and light-intensity walking on biomarkers of cardiometabolic health in adults: A systematic review and meta-analysis. Sports Med 2022;52:1765-1787.
Sedentary lifestyles are dangerous for health. Defined as any waking behavior expending < 1.5 metabolic equivalent tasks while seated or reclined, prolonged sedentary behavior has been linked to many markers of poor health, including increased waist circumference and higher levels of C-reactive protein.1
The authors of recently published studies have found interruptions of sedentary behavior (also known as sedentary breaks) are associated with several health benefits, including improved systolic blood pressure, higher HDL cholesterol levels, lower postprandial insulin and glucose readings, and smaller waist circumference. The relationship between intensity of exercise during a sedentary break and health benefits is not yet defined.2,3
To begin clarifying the association between the type of sedentary break and biomarkers of cardiometabolic health, Buffey et al conducted a comprehensive review and meta-analysis of one-day experimental studies (conducted in lab settings) comparing prolonged sitting in adults with sitting interrupted by standing and sitting interrupted by light-intensity walking. To be eligible for this study, trials needed to include adult men and/or women as participants; measure at least one biomarker of cardiometabolic health; and include prolonged sitting (at least five hours), standing, and light-intensity walking among the study arms. The authors identified seven such studies, five from the United Kingdom and two from the United States, for the final review and meta-analysis.
Despite meeting all inclusion criteria, the seven studies were significantly heterogeneous in methodology, including frequency and duration of breaks, the definition of light-intensity walking, meals provided to participants, and measurement techniques for the biomarkers (continuous monitoring vs. periodic blood collection) as well as the biomarkers measured. Although some studies measured factors such as diastolic blood pressure, cholesterol, and triglyceride levels, the biomarkers included in this systematic review and meta-analysis were postprandial glucose, insulin, and systolic blood pressure. These were chosen because each of them was measured in at least three of the included studies, allowing sufficient data for a valid meta-analysis. Specifically, all seven studies measured postprandial glucose, four of the studies measured postprandial insulin, and four of the studies measured systolic blood pressure.
Differences are reported in terms of Cohen’s d, which often is used in social sciences to determine the magnitude or practical significance of an intervention, especially when there are multiple variables or outcomes.4 Scientists determine Cohen’s d by calculating the standardized difference between two means (mean of Group A - mean of group B ÷ pooled standard deviation.) In general (and for this study), effect size is defined as small effect: 0.2, medium effect: 0.5, and large effect: 0.8. It is interesting to note effect size and statistical significance differ. One way to think about this is to consider that effect size reflects the importance or clinical relevance of the result (e.g., a medium effect size is a result that should be visible to “the naked eye”) while statistical significance or P value indicates the likelihood of the result occurring by chance.4,5 It also is useful to note that in this study, a negative effect size implied an improvement in biomarkers (decrease in value of postprandial glucose, postprandial insulin, and/or systolic blood pressure).
Upon analysis of subgroups according to body mass index, researchers found that among the walkers, larger improvements in postprandial glucose occurred in normal and overweight participants when compared to obese participants (P < 0.04).
COMMENTARY
This ambitious systemic review and meta-analysis of studies of markers of health associated with two different types of sedentary breaks (standing and light-intensity walking) adds to a growing knowledge base regarding health benefits of interruptions to a sedentary lifestyle.1-3 Specifically, the results of this study point to advantages of light-intensity walking vs. standing as a break from prolonged sitting. Although the heterogeneity of the covered studies precluded answering some obvious clinical questions (such as how long a break should last and how often a break should be initiated) it is likely that, with the promising results found here, these are areas for future investigation. However, it is useful to note that, on average, most of the studies interrupted sitting for about 28 minutes.
Additionally, Buffy et al noted future investigators should standardize methodology and include a consistent mechanism to measure cardiometabolic markers, including but not limited to when and how to measure changes in systolic blood pressure and how to best evaluate changes in levels of glucose and insulin. Another feature of this meta-analysis was the fact all included studies were limited to one-day laboratory trials. This clearly limits the generalizability of the findings. However, the potential clinical implications of these findings are significant. Light-intensity walking is a practical intervention that can be implemented in various work environments. Additionally, employers may be attracted to this intervention because of its relatively low cost and ease of implementation. Even with the noted limitations, this review and meta-analysis carries value for healthcare providers working with patients to design wellness plans. This study can serve as a reminder that some benefits of exercise do not require a gym, strenuous effort, or even measurable weight loss. Instead, incremental changes in markers of cardiometabolic health can be attained by standing and amplified even more by light walking.
REFERENCES
- Healy GN, Matthews CE, Dunstan DW, et al. Sedentary time and cardio-metabolic biomarkers in US adults: NHANES 2003-06. Eur Heart J 2011;32:590-597.
- Benatti FB, Ried-Larsen M. The effects of breaking up prolonged sitting time: A review of experimental studies. Med Sci Sports Exerc 2015;47:2053-2061.
- Paterson C, Fryer S, Zieff G, et al. The effects of acute exposure to prolonged sitting, with and without interruption, on vascular function among adults: A meta-analysis. Sports Med 2020;50:1929-1942.
- Glen S. Cohen’s d: Definition, examples, formulas. StatisticsHowTo.com.
- Bradburn S. What is and how to calculate Cohen’s d. Top Tip Bio.
The authors of this meta-analysis explored the effects of interrupting sitting with either light-intensity walking or standing. They found light-intensity walking was associated with the most significant effect on several markers of cardiometabolic health.
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