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INTRODUCTION
South America is comprised of nations and territories containing different environments and many complex and heterogeneous ethnicities, societies, and cultures in a population estimated at over 430 million. In South America upper-middle-income economies are predominant, and major demographic shifts like population growth, urbanization, technological advancements, and ageing are in course (1). Thus, behavior and environment factors, such as smoking, unhealthy diets (i.e., high energy-rich foods and low fruit and vegetables consumption), and physical inactivity are relevant modifiable risk factor for cardiometabolic diseases (CMD) (2 3 4 5-6).
Concerning physical inactivity, sedentarism is known to bring about serious health consequences and associations with all-cause mortality and other outcomes worldwide (2,7 8 9-10). Despite the fact that one in four adults worldwide does not meet the World Health Organization recommendations on physical activity to benefit from a reduced risk of common chronic diseases (11), failing to achieve the public health goals on physical activity is not the same as being sedentary. In this sense, sedentary behavior (SB) refers to activities that do not require significant energy expenditure – i.e., 1.5 METs or lower (12) – and is usually expressed as sitting time (ST) (13) such as in television (TV) viewing, computer use, transport, driving, reading or playing video games whilst in a sitting or reclining posture (14), in different everyday life domains (i.e., home, workplace, commuting, leisure time) (13,15). Sedentary behavior has been independently associated with detrimental health outcomes, including CMD, in adults from different regions worldwide (16-19). Moreover, SB presents high values in populations of different ethnic background worldwide (20) – among adults, the proportion of individuals spending 4 or more hours a day in a sitting position varies from 23.8 % in Southeast Asia, 37.8 % in Africa, 39.8 % in the western Pacific, 41.4 % in the eastern Mediterranean, and 55.2 % in the Americas to 64.1 % in Europe (21).
In South America's adult population physical inactivity reaches levels of over 40 % (21), and SB has been assessed as almost 6 h/day (22). In addition, the prevalence of CMD and its risk factors in South America is high (4,6,23,24). Nevertheless, the association between SB and CMD and its risk factors in South Americans is not well known. Identifying the association of SB in different domains with CMD is not only important for public health interventions, but also for occupational health, urban planning, and transport-related initiatives. Therefore, the aim of this study was to systematically review the literature to examine whether domain-specific SB is associated with CMD and related biomarkers in South American adults.
METHODS
SEARCH STRATEGY
A broad and specialized search was performed. Studies reporting on the possible association between SB and/or domain-specific SB – e.g., ST, TV viewing time or frequency and overall SB (sedentary activity, screen time, computer time, reading time, passive transport, and sedentary work) – with CMD diseases (primary outcomes) and or related biomarkers (secondary outcomes) in South American adults were examined. The reporting guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement were followed, and the criteria outlined in A Measurement Tool to Assess Systematic Reviews (AMSTAR) checklist (25,26) were observed. The methodology of this systematic review was prospectively registered with PROSPERO (CRD42018099319;http://www.crd.york.ac.uk/PROSPERO) under the title “Is sedentary behavior associated with risk for cardiometabolic diseases in South American adults? A systematic review”.
This review examined studies completed from January 2010 to December 2018, written in English, Spanish or Portuguese or with translations into these languages. Relevant studies were identified using the following electronic databases: Medline (Medical Literature Analysis and Retrieval System Online /PubMed); Embase (Elsevier); Cochrane Central (The Cochrane Central Register of Controlled Trials The Cochrane Library); Lilacs (Scientific and technical literature of Latin America and Caribe); Science Direct; Bireme (Latin American and Caribe center of information in health science); Scielo.org; Scopus (Elsevier); and SPORTDiscus.
The exposure descriptors used were: a) “sedentary behavior or time or lifestyle”; b) “sitting or reclining or leisure time”; and c) “television or TV view or watch or time”. The outcome descriptors used were: a) “cardiometabolic or metabolic health or markers or risk or disease or syndrome”; and b) “cardiovascular or CVD markers or risk or disease or syndrome”. The population descriptors used were: a) “South America or South American countries and territories”. Appropriate combinations of these descriptors were used to ensure quality, transparency and maximum sensitivity during article retrieval. The search strategies adapted to the indexing systems are available from the authors upon request.
STUDY SELECTION
This review included studies that addressed the amount of time spent in SB or domains of SB as risk factors for CMD, either self-reported or objectively measured, reported on a continuous scale (e.g., minutes/day) or divided into categories (e.g., > 3 h of TV time vs. ≤ 3 h), and time spent in specific domains of SB (i.e., ST, TV time or frequency and overall SB). The presence of CMD such as obesity, diabetes, hypertension, metabolic syndrome (MetS), and a clustering of chronic diseases (CCD - Heart attack, heart failure, angina, hypertension, DM, or arthritis) were the primary outcomes of interest in this review. Related biomarkers like total cholesterol (TC), high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol, triglycerides (TG), blood glucose and insulin, glycated hemoglobin (HbA1c), insulin resistance (HOMA-IR), hypercholesterolemia, dyslipidemia and anthropomorphic measures such as body mass index (BMI), waist circumference (WC) and percentage of body fat (% BF) were the secondary outcomes of interest. Articles excluded were those on non-South American populations and/or non-adult populations (mean age < 18 years), those that did not report exposure to SB or the association between SB and health outcomes, those that were duplicated, impossible to locate or obtain, and reviews or meta-analyses.
The screening of titles and abstracts for all studies was independently performed by two authors (KAM and AJN) in order to identify potential relevant articles. Likewise, these two authors (KAM and AJN) performed full-text screenings, and with mutual consensus confirmed that studies met the study's inclusion and exclusion criteria. The authors resolved discrepancies after discussion.
DATA EXTRACTION AND ANALYSIS
Data and informations of interest were extracted by KAM or AJN. The main information obtained was on study characteristics, population characteristics, country of study, sample size analyzed, SB exposure and methods, outcome measurement, and measure of effect or correlation. Study quality was assessed using an adapted 20-item checklist (originally 27 items) of the Downs and Black checklist (27). Good quality was determined by using the overall numeric score of quality out of 20 possible points. Studies showing 16/20 median split or higher were considered of high quality. KAM independently assessed quality using the checklist, and AJN reviewed all scores. Disagreements were resolved upon consensus or were refereed by a third researcher.
The study-specific ORs for obesity or diabetes were combined as a generic inverse variance to estimate the pooled OR with 95 % CI by using the inverse variance statistical method with a random effects model. The pooled OR was calculated from a natural logarithm of OR [ln(OR)] and the standard error of ln(OR) was obtained for the 95 % CI. A two-sided p-value lower than 0.05 was considered significant for all analyses. Studies were not included in the meta-analysis if the summary statistics of OR and 95 % CI were not available (31), or when the subjects evaluated were not sedentary (29). This meta-analysis was conducted using the RevMan 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, 2012), a free download athttp://tech.cochrane.org/revman/download
RESULTS
The search identified 1,262 articles, and the screening of their primary titles and abstracts generated 262 articles. Then these 262 articles were reviewed in full and 20 articles met the inclusion and exclusion criteria. Figure 1 shows the flow diagram and the reasons for exclusion. In all, 55 % of the analyzed studies were considered to be high-quality. Five out of 20 studies scored 17 points; six scored 16 points, eight scored 15 points, and one scored 14 points.
Figure 1. Flow diagram for literature search, January 2010 – December 2018. (SB: sedentary behaviour. Source: prepared by the authors from the study results).
In this review eleven out of the 20 analyzed studies were carried out on Brazilian, seven on Chilean, one on Colombian, and one on Peruvian adults, and were published prior to and including December 2018, specifically from 2010 to 2018. We observed that most studies were published from 2017 on (n = 11). The selected studies analyzed adults (mean age: 30 to 70 years) from urban (n = 20/20) and rural (n = 8/20) areas.
The qualitative analysis revealed that 13 out of 20 studies reported on CMD (obesity, diabetes, hypertension, CCD, and MetS) (Table I), and 16 studies reported results related to CMD biomarkers. Overall, the results were consistent in showing that an increase in time spent in SB was associated with an increase in obesity (n = 8/8), diabetes (n = 6/7), CCD (3/4), hypertension (n = 3/4), and MetS (n = 2/2). Along with these diseases, SB was associated with high values of the following related biomarkers (Table II): BMI (n = 8/9), waist circumference (n = 7/7), % BF (4/4), HOMA-IR (n = 4/4), glucose (n = 5/6), insulin (n = 4/4), and TG (n = 4/6), and low levels of HDL-c (n = 4/6). Dyslipidemia (1/1) and hypercholesterolemia (1/1) were also positively associated with SB. Despite that, TC (n = 3/6), and LDL-c (n = 3/5) were associated with SB in only three out of six and five studies, respectively. Regarding HbA1c (1/2), this glycemic control biomarker was associated with SB in only one study.
Table I. Cardiometabolic diseases (primary outcomes) reported in the included studies looking at its association with sedentary behavior in South American adults, January 2010 to December 2018
*p < 0.05;
†p < 0.01. Source: prepared by the authors from the study results.. AO: abdominal obesity; aOR: adjusted odds ratio; aPR: adjusted prevalence ratio; BMI: body mass index; CI: confidence interval; CO: central obesity; CD: chronic disease; DM: diabetes mellitus; HC: hypercholesterolemia; Li: lower limit; MetS: metabolic syndrome; NR: not reported; OR: odds ratio; PA: physical activity; QA: quality assessment; ROC: receiver operating characteristic; SA: sedentary activity; SB: sedentary behavior; ST: sitting time; TV: television; TC: total cholesterol; WC: waist circumference.
Table II. Related biomarkers (secondary outcomes) of included studies looking at the association of sedentary behavior and cardiometabolic diseases in South American adults, January 2010 to December 2018
aPR: adjusted prevalence ratio; BMI: body mass index; HbA1c: glycated hemoglobin; HOMA-IR: homeostasis model assessment-insulin resistance; HDL-c: high density lipoprotein-cholesterol; IPAQ: International Physical Activity Questionnaire; LDL-c: low density lipoprotein-cholesterol; OR: odds ratio; % BF: percentage of body fat; QA: quality assessment; SA: sedentary activity; SB: sedentary behavior; ST: sitting time; TV: television; TC: total cholesterol; TG: triglycerides; WC: waist circumference. Source: prepared by the authors from the study results.
CARDIOMETABOLIC DISEASES (PRIMARY OUTCOMES)
The association between SB and CMD as primary outcome was observed in different studies (Table I). For example, high SB ( > 4 h/day) was associated with central obesity in Chilean adults (28); and those categorized as either low SB (i.e., ST of 1.56 ± 0.7 h/day) or high SB (i.e., ST of 5.31 ± 2.2 h/day) and physically active were less likely to have obesity or central obesity when compared to those in the high SB (i.e., ST of 6.14 ± 2.6 h/ day) and inactive category (29). In addition, Chilean men exhibiting a higher ST were more likely obese (30). A ST of over 8 h/day during the week discriminated the presence of abdominal obesity, but not of obesity in Brazilian women (31); and obesity was associated with SB in Brazilian adults (32). Furthermore, a higher TV time was associated with greater abdominal obesity (33) and obesity (34) in Brazilian and Peruvian (35) women. The pooled odds ratio for obesity in association with sedentary behavior – 1.30 (1.14-1.49) – is presented in figure 2.
Figure 2. Pooled odds ratios for obesity in association with sedentary behavior. (CI: confidence interval; SE: standard error. Source: prepared by the authors from the study results).
Regarding DM, an overall sedentary time and TV time ≥ 3 h/day (36) or ≥ 4 h/day (37) was positively associated with DM in Brazilian adults. Likewise, ST ( > 4 h/day) was positively associated with DM in Chilean adults (2,28). Furthermore, Chilean adults categorized as with either low or high SB and physically active were less likely to have DM, as compared to those in the high SB and inactive category (29). Finally, a ST of more than 5.5 h/day was positively associated with a high likelihood of having DM in Brazilian older adults (38). However, in Brazilian workers a high SB time (i.e., TV viewing, passive transport, sedentary work, and sedentary lifestyle) was not associated with DM (32).
The pooled odds ratio for diabetes in association with sedentary behavior – 1.16 (1.07-1.25 – is presented in figure 3.
Figure 3. Pooled odds ratios for diabetes in association with sedentary behavior. (CI: confidence interval; SE: standard error. Source: prepared by the authors from the study results).
Concerning CCD, Brazilian men who used a passive form of transport to go to work, and had a sedentary job and sedentary lifestyle were more likely to have > 2 CDs, whereas women who reported ≥ 3 hours/day of TV time were more likely to have one CD versus no CD (32). TV time > 4 h/day was positively associated with the presence of heart disease (i.e., heart failure, heart attack, and angina) among Brazilian adults (37). Moreover, Brazilian adults who spent > 4 h/day sitting had a higher risk for the presence of > 2 CDs (39). Nevertheless, Brazilian adults diagnosed with > 2 CDs exhibited a similar amount of daily ST (~ 4 h) as compared to those diagnosed with zero or one CD (40).
As regards hypertension, it was positively associated with high TV time ( > 4 h/day) in Brazilian (32) but not in Chilean adults (28). Moreover, Chilean and Brazilian adults categorized in the high overall SB or high SB at work groups, respectively, had a high occurrence of hypertension (29,32).
With reference to MetS, Chilean adults in the low or high SB and physically active group were less likely to have MetS when compared to those in the high SB time and inactive category (29). In addition, high ST ( > 4 h/day) was positively associated with MetS among Chilean adults (28).
RELATED BIOMARKERS (SECONDARY OUTCOMES)
The association between SB and CMD-related biomarkers was also reported in the reviewed studies (Table II). Regarding BMI, its positive association with SB was found in Chilean adults (29,41 42-43) and in Colombian men (44). Such association was also reported in Chilean men only (2), whereas a positive association of TV frequency with BMI was observed in Brazilian (34) and in Peruvian women only (35). However, SB ( > 4 h/day) was negatively associated with BMI in Chilean women, but positively in Chilean men (28). In addition, ST ( > 4 h/day) was not associated with BMI in Brazilian adults (45). Concerning % BF, it was positively associated with sedentary behavior and ST in Chilean adults (41 42-43) and in Colombian men (44).
With regard to WC, its positive association with SB was reported in Brazilian (33) and Chilean (2) women. Chilean adults categorized as 'high SB-active' or 'low SB-active' showed significant negative associations with WC when compared to those in the 'high SB-inactive' category (29). Moreover, in Chilean adults a high ST was positively associated with WC (41). Furthermore, per one-hour decrease in sedentary time, there was a significant decrease in WC among Chilean adults (42). SB was also positively associated with WC in Colombian men (44), whereas SB, but not ST, was positively associated with WC in Chilean adults (43).
With respect to blood glucose, a positive association between ST and fasting glycemia was found in Chilean adults (29,41 42-43), whereas such association was not observed by others among Chilean adults (2) and in Colombian men (44).
A positive association of ST with fasting insulinemia was observed in Chilean adults (41 42-43) and in Colombian men (44). Furthermore, SB was positively associated with HOMA-IR in Chilean adults (41 42-43) and in Colombian men (44). Regarding HbA1c, Chilean 'high SB-active' adults showed lower values of HbA1c when compared to those in the 'low SB-active' category (29). However, no association of SB with HbA1c was reported for Chilean adults (2).
Chilean adults exhibited a positive association of ST with serum lipids (41 42-43). Likewise, ST was positively associated with serum TG and HDL-c levels among Colombian men (44). Notwithstanding this, ST during the week or weekend did not discriminate any serum lipid abnormalities in Brazilian women (31). Moreover, Chilean adults in the 'high SB-active' or 'low SB-active' groups showed no significant associations with an abnormal serum lipid profile (29). Furthermore, Suárez et al. (44) observed that ST was not associated with serum TC and LDL-c levels in Colombian men. Regarding hypercholesterolemia, Garcia et al. (32) found that in Brazilian workers SB at work was positively associated with hypercholesterolemia. In addition, a higher adjusted prevalence ratio of dyslipidemia was reported among Brazilian women with a more prolonged ST (46).
SUBGROUP ANALYSES
Subgroup analyses for sex and domain-specific sedentary behavior were performed. Between-sex differences were found in some studies. For instance, obesity (30) and BMI (2) were found to be positively associated with ST in Chilean men only, whereas it was negative in women (28). Waist circumference was found to be positively associated with SB in Chilean women only (2). Among Brazilians, BMI and obesity were positively associated with SB in women only (34). Moreover, SB at work was positively associated with chronic diseases (e.g., obesity, hypertension, CCD, and hypercholesterolemia) especially in men as compared to women (32). Finally, a higher adjusted prevalence ratio of dyslipidemia was reported for Brazilian women but was not reported for men (46).
The investigation of the association of domain-specific SB with CMD and related biomarkers found that 12 studies reported on ST (2,28-31,38-41,44-46) and four on TV time or TV watching frequency (33-35,37). The remaining four studies looked at general measures of SB (32,36,42,43). The results demonstrate equivalent trends for each SB domain.
DISCUSSION
In this review we thought to systematically review the literature to examine whether domain-specific SB is associated with CMD and its risk factors in South American adults. This is the first review to explore the association of SB with CMD and its risk factors in South American adults. This study summarized the published evidence over the review period (i.e., January 2010 to December 2018), and observed that longer SB (i.e., sitting, TV watching, overall SB time) was associated with CMD (i.e., obesity, DM, and CCD) as well as with its anthropometric (i.e., BMI, WC, and % BF) and metabolic biomarkers (i.e., lipid profile and glucose). Nevertheless, evidence is limited when studies reported the relationship between SB and CMD (i.e., hypertension and MetS) as well as its biomarkers (i.e., HOMA-IR, BI, dyslipidemia, and hypercholesterolemia). It has to be taken into consideration that reports on the associations of SB with hypertension, MetS, HOMA-IR, insulin, dyslipidemia, and hypercholesterolemia are scarce.
Our results complement the previous evidence from systematic reviews (17,18,47) and meta-analyses (16,19,48), which demonstrate that high SB is associated with CMD and risk factors in different regions of the world. Based on the studies reviewed here, South American adults are likely at larger risk for developing obesity, diabetes, and CCD when incurring in prolonged SB time. Such findings are consistent with those reported about different populations (18,19,48). A significant association of longer time spent in SB was found with obesity (8 studies), DM (6 but 1 study), and CCD (4 studies) in the 20 studies reviewed. For instance, South American (i.e., Chilean) adult men in the highest tercile of ST had a 97 % higher risk for obesity (30). In addition, Lemes et al. (36) reported a 60 % higher risk for diabetes in South American (i.e., Chilean) adults who spent ≥ 3 h/day in sedentary activities, whereas those South American (i.e., Brazilian) men and women who reported a daily ST of 4 h had a 76 % and 82 % higher risk of presenting ≥ 2 CCDs, respectively (39). However, the magnitude of the risk of developing DM with longer sedentary time is approximately twice as high as in the general population and, in general, longer sedentary time is associated with a 14 % greater risk of cardiovascular disease (19). A significant relationship between increased SB and higher BMI (8 but 1 studies), WC (7 studies), and % BF (4 studies) was also reported in the reviewed studies. These results are similar to those previously reported in different populations (49,50) and, more importantly, are consistent with the association of longer time spent in SB with obesity as observed in the present review.
Concerning sex differences, only seven studies reported distinct associations of SB with CMD and its biomarkers. Based on those studies, it appears that South American men are at higher risk for obesity and high BMI when spending a lot of time in SB, as compared to women. Such finding is contradictory to the report that women are more inactive (33.9 %) than are men (27.9 %) worldwide (21). Regarding domain-specific SB in South American adults, most studies associated a higher risk for CMD with longer periods of ST (13 studies), which was followed by the extent of TV (6 studies) and SB (4 studies) times. Whether there are distinct health damages for the different specific domains rather than length of exposure is not known, and thus demands further investigation.
Overall, this systematic review presented a positive association between SB and CMD in South American adults. Whether these risks are truly greater in this population group further studies are needed to elucidate, inasmuch as the insufficiency of available direct evidence on this sub-population limits the ability to ascertain such findings. Despite this, the findings presented here are of relevance for South American governments, since they reinforce the need for public policies to face the deleterious consequences of a sedentary lifestyle.
STUDY LIMITATIONS
This review has some limitations. First, there is a lack of studies examining the relationship of SB with CMD and related biomarkers in South American adults, which make it difficult to generalize our findings. Eleven out of 20 analyzed studies were carried out in Brazilian, seven in Chilean, one in Colombian and one in Peruvian adult men and women. Although the population of these four countries accounts for 73 % (~ 316 million people) of the South American population, no data on adults from the other South American countries were found. Moreover, the selective reporting of positive outcomes in individual studies could potentially reduce the generalizability of our findings. Secondly, the predominant use of self-reported data in individual studies is another limitation, since self-reported data are highly susceptible to biases that might have affected the magnitudes of our results. Only three studies in the present review reported on the use of objective measures (accelerometers) of SB time in Chileans (Leiva et al., 2017; Salas et al., 2016; Celes-Morales et al., 2012), but did not assess the association of SB with CMD as their primary outcome. Finally, despite the quality of the selected studies, all 20 studies were cross-sectional in design, and as such they may include selection and reverse causality biases, as well as residual confounders. Therefore, since there is no temporality described between the sedentary behavior and the outcomes, interpretations should be cautious.
CONCLUSIONS
In conclusion, spending a long time in an overall SB, mainly in a sitting position or watching TV, was positively associated with the occurrence of CMD (i.e., obesity, diabetes, and ≥ 2 CCDs) and related biomarker (i.e., BMI, WC, % BF, lipid profile, and blood glucose) elevations in South American adult men and women.
