This study is unique because it evaluates the association between the ratio variable, represented by MVPA/SB, and the CVR outcome variable. In addition, we investigated the combined association between the MVPA/SB ratio and sleep on CVR. Finally, we explored a hypothesis that postulates the mediating role of sleep in the association between the MVPA/SB ratio and CVR, thus providing a significant contribution to the epidemiological and public health literature. This study found that individuals with ≥ 2.5 minutes of MVPA per hour of SB were less likely to be at risk of cardiovascular events, both directly and mediated by sleep. Furthermore, in the combined analysis, individuals with the two factors (≥ 2.5 minutes of MVPA per hour of SB + good sleep quality) was less likely to have an intermediate to high CVR.
Recent literature has highlighted the importance of considering the full 24 hours of movement, rather than just one isolated behavior when assessing general health[14]. Over the course of a daily cycle, individuals devote as much time to PA as they do to SB and sleep. Tremblay et al. (2016)[14] observed that focusing on the entire 24 hours is more important for health than a fragmented analysis of these behaviors. Thus, a model of guidelines has been promoted that considers the interrelationships between movement behaviors for health, rather than considering isolated recommendations[7, 35, 36].
Thus, our study sought to investigate how the influence of movement behaviors is associated with cardiovascular risk. The benefits obtained through the practice of PA in CVR are irrefutable and can be corroborated in the literature. Cross-sectional studies show the fundamental role of regular PA not only in reducing the prevalence, but also in reducing the incidence of risk factors associated with cardiovascular events[37, 38]. These findings are corroborated by clinical trials, which have consistently shown that regular PA promotes significant improvements in various cardiovascular risk markers, including BMI, waist circumference, blood pressure, glycemic control and insulin resistance. In addition, an optimization of the lipid profile is observed, with significant reductions in low-density lipoprotein (LDL) cholesterol levels and increases in high-density lipoprotein (HDL) cholesterol[39],[40],[41].
With regard to SB, although the causal relationship with CVD still needs to be investigated; some research suggests an association between them[42]. In a meta-analysis, SB was associated with an increased CVR in individuals who spent more than 10 hours a day in a sitting position[43]. Corroborating, a systematic review that aimed to assess the magnitude of the dose-response relationship between SB and CVD, an increase in the risk of CVD mortality was observed in individuals who spent prolonged periods in a sitting position. The analysis indicated a significantly elevated CVR in people who spent more than 8 and 6 hours a day in SB, associated with an approximate 5% increase in the risk of mortality in these cases[44].
Hamilton et al (2004)[45] provided convincing evidence to support the association between prolonged time in SB and adverse effects on cardiovascular health. These effects are largely attributed to unbalanced physiological mechanisms due to the lack of stimulation of musculoskeletal contraction over a prolonged period. Sitting for too long can result in the inhibition of skeletal muscle lipoprotein lipase (LPL) activity, which plays a crucial role in the uptake of triglycerides and the production of HDL, as well as reducing glucose uptake.
It should be noted that even small muscle contractions are essential for cardiometabolic health. In this context, current guidelines have emphasized the importance of interrupting sitting time, recommending standing for at least 5 minutes every 1 hour in the SB. Therefore, even low-intensity PA, such as walking around the house, have the potential to interrupt time in SB and provide substantial protection against disorders involving impaired lipid metabolism, emphasizing the importance of incorporating regular movement throughout the day to maintain cardiovascular and metabolic health[46, 47].
The literature has shown evidence of a dose-response relationship between the daily time devoted to MVPA and SB with the risk of all-cause mortality[48–50], showing that MVPA attenuates the increased risk of prolonged periods of SB. Chastin et al. (2021)[29] identified dose-response associations between the balance of time dedicated to MVPA and SB with all-cause mortality. The authors observed that practicing 2.5 minutes or more of MVPA per hour of SB daily was associated with a reduction in the risk of all-cause mortality similar in magnitude to that obtained by following the current PA guidelines of the World Health Organization (WHO)[29].
Concerning sleep quality, it is also widely recognized that this behavior plays a fundamental role as a determinant of individual health[42]. Accumulating evidence points to an association between sleep quality and an increased risk of various cardiometabolic risk factors, cardiovascular disease, and all-cause mortality[43, 44]. However, to the best of our knowledge, no study has explored the role of sleep as a mediator in the relationship between the MVPA/SB ratio. Our results reveal that sleep has a significant effect on this association with CVR, suggesting its importance as a key mediator in this interrelationship of movement behaviors. These mediantion can occur because MVPA and SB may, potentially, affect the sleep quality, and sleep quality can affect the CVR, as above mentioned.
In fact, SB emerges as a component correlated with poor sleep quality. This association is due to the influence of SB on melatonin suppression, especially due to prolonged exposure to screens and blue light, which stimulate psychophysiological arousal, causing an imbalance in internal biological rhythms impairing sleep quality[51, 52]. While SB shows a negative association with sleep quality, regular PA practice seems to have positive effects on sleep, since it helps to improve sleep time and quality, through its effects on different systems, including the metabolic, endocrine, vascular and immune systems, as well as aspects related to mood and circadian rhythm[53–55]. In terms of physiological mechanisms, PA is associated with changes in neuroendocrine systems, such as the release of endorphins and the regulation of cortisol, which can positively influence sleep architecture[56–58]. In addition, body temperature, which is modulated by PA, has been shown to be a key element in the regulation of the sleep-wake cycle [59].
In a cross-sectional compositional analysis study involving 1937 adults, it was observed that the distribution of time dedicated to sleep, SB, LIPA and MVPA is significantly associated with a series of anthropometric measures and biomarkers related to cardiovascular health. The proportion of time spent on LIPA and SB showed a negative association with obesity and cardiovascular disease markers, but the association with SB was stronger. Furthermore, within the composition of time dedicated to activities, the proportion of time spent on MVPA exhibited the strongest positive effect, especially when it replaced time dedicated to SB[35]. In line with this, a prospective cohort study conducted in the United States, involving 1,718 adult participants, identified that replacing 30 minutes of SB with time dedicated to sleep, LIPA and MVPA showed a positive and significant association with a higher cardiovascular health score (CVH). The MVPA showed a stronger association compared to sleep and LIPA[43].
Considering contemporary technological advances and the nature of the occupations performed, it is undeniably difficult to contain the long hours dedicated to sitting, especially in computerized environments. In this context, there is a need to develop new guidelines for the practice of PA in order to mitigate the adverse health effects associated with prolonged sitting. We recognize that the ideal scenario for the health and well-being of the population is a balance between the practice of PA and minimizing exposure to long periods of sitting.
That said, our results support the hypothesis that movement behaviors represent significant factors for CVR management. Furthermore, we found that MVPA emerges as a crucial determinant for attenuating the detrimental effects of SB and poor sleep quality on CVR, which is in line with the existing literature. Therefore, we reiterate the importance of adopting a lifestyle that promotes regular PA practice, good sleep quality and minimizing the time spent in SB.
Strengths and limitations
As far as we know, this is the first study to investigate sleep mediation in the association between the minutes of MVPA per hour of SB and CVR, which is a strong point of the study. Also noteworthy is the face-to-face data collection methodology, probabilistic sampling, weighting of the sample and data, indicating greater reliability of the results found.
However, despite these strengths, our findings are not without their limitations. The practice of MVPA, SB and sleep were estimated through the self-report of individuals and may suffer from memory bias, overestimation or underestimation of the data. In addition, the data in this study was collected during the covid-19 pandemic, and social restriction had a direct impact on the time spent on SB and on MVPA practice. The cross-sectional design of the study does not allow causal inferences to be drawn between MVPA, SB and sleep on CVR. In addition, other well-known risk factors, such as inflammatory markers and coronary calcium score, are not incorporated into the FRS calculation, which may underestimate or overestimate the CVR. Therefore, the data should be interpreted and disseminated with caution.