To the authors’ knowledge, research on the relationship between distinct SB domains and mental health outcomes through a positive perspective is very scarce [40]. We found that SB was highly prevalent among the participants in the occupational pursuits. Our data indicated that all the domains of SB were negatively associated with PWB. Occupational SB and transport-related SB were negatively correlated with GLS, and leisure-time SB and occupational SB were negatively associated with MCS-12 in the unadjusted mode. In the adjusted model, the associations were attenuated, and only occupational SB remained negatively associated with GLS. Thus, taken together with the results of the present investigation, our findings differ from those of Scarabottolo et al. (2022) [40], where it was reported that screen time (i.e., watching television, using computers, and cell phones – without clarifying if for leisure or occupational purposes) may be negatively associated with social functioning (component of HRQoL) but positively related to other components (i.e., physical functioning, role-physical and role-emotional) after two years of follow-up.
Although the mechanisms linking SB with mental health are still unknown, several hypotheses may be suggested. First, SB takes time away from PA, which in turn is responsible for the prevention and treatment of diseases or conditions that impair well-being (such as depression and anxiety) [41], possibly due to the mediation of biological factors (such as interleukin 6 and brain-derived neurotrophic factor [BDNF] release during exercise). In addition, there are clinical factors (such as global functioning and frequency of physical symptoms), psychological factors (life satisfaction and self-esteem) and social factors (such as social support and marital status) associated with PA [42] that can also affect mental health. Second, longer sitting time has been associated with social isolation (i.e., physical, social, or psychological separation from individuals or groups) [43] in adolescents [44] and in older people [45], and the evidence shows that socially isolated people are more likely to suffer from suicidal thoughts [46] and depression [47].
Recognizably, there are studies showing associations between lifestyle factors and depression; thus, after the adjustment for age, sex, compliance with PA guidelines, BMI, smoking history, chronic disease status, financial perception, and sleep (quality and duration), there was an expected attenuation of the negative relation between SB domains and well-being outcomes. As a result, only the negative relation for occupation SB with GLS remained (p<.001), meaning that this relation was stronger and that it may be independent from the covariables included in the model.
4.1 Findings in young adults
Our second goal was to identify whether the associations between SB domains and mental health outcomes differed with age. Our analyses indicated that leisure-time SB was negatively associated with PWB (p=0.008) in young adults (18 to 24 years old), but we found no associations for the other SB domains, except for an unexpected positive association for transport-related SB with MCS (p=0.034).
One of the reasons why leisure-time SB may be negatively associated with PWB in young adults may be due to a reduction in PA during leisure time (competing with SB), which has been associated with higher levels of PWB with a positive impact on self-acceptance, positive relations with others and purpose in life [48]. In addition, the domain of PA is important. A study that evaluated the relation between different domains of PA and positive mental health in 456 men (mean age 29 years) indicated that only PA during leisure time was associated with better mental health, and no association was found for the commuting and occupational PA domains [49]. Another reason for leisure-time SB being negatively related to PWB may be that younger adults (recently emerged from adolescence) spend much of their leisure time in front of screens [22], as they are the largest users of social networks (such as Instagram® and TikTok®). In fact, a 2022 survey [50] reported that nearly all American teens (95%) have access to a smartphone (with few differences between income brackets [from 93% to < $30.000 to 96% >$75.000]), and 45% are "almost constantly" connected. Likewise, this phenomenon extends to young adults, where 96% of individuals from 18–29 years old report having a smartphone [51], with approximately 70% of them indicating daily use. Although not all studies corroborate the negative impact of social media on the PWB and mental health of young people [52], [53], with its use being important and facilitating social connection and support [54], it can certainly harm PWB, mainly depending on how, with whom, and why social media is used [55].
In addition, recent investigations have shown that younger people are the most exposed to various types of content, potentially criminals (cyberbullying, cyber-dating violence, sextortion, sexting, revenge porn, online dating, catfishing, and scammers) [56], with potential consequences on mental health [57]. Finally, in the younger group (18 to 24 years), the time spent in occupational SB was not associated with well-being outcomes, even acknowledging that they were the group spending more time in occupational SB (i.e., spending more 57 min/day than adults). This can possibly be justified by the younger adults of our sample, being predominantly students, spending its time in an occupational, educational environment, which can be perceived as a time dedicated to a purpose and direction in life, as a choice task that will bring meaning and benefits to society and themselves, while the adults are predominantly employees (staff and teachers).
We found an unexpected positive relationship between transport-related SB and MCS-12, but the nature of our study, coupled with the lack of similar evidence, prevent us from making inferences on this topic. A previous study evaluated the relation of inactive transportation and psychological stress (that is, from a negative perspective) and did not find any relationship with psychological stress[58].
4.2 Findings in adults
In adults (≥ 25 years), after all the adjustments, occupational SB was negatively associated with GLS (p<.001) and MCS (p=0.018), and transport-related SB was negatively associated with PWB (p=0.025). In contrast to what happened in the younger group, leisure-time SB was not associated with well-being outcomes. Our cross-sectional observations are in line with the results from an experimental study with 146 office workers that assessed the efficacy of SB reduction through the use of standing desks versus a control group, while using objective measures and found a significant reduction in sitting time (-83.28 min/working day after 12 months) with repercussions in a reduction in daily anxiety after 6 and 12 months and an improvement in quality of life [59], providing insights that sitting time in the work setting can be harmful to mental health in adults. In addition, an investigation with more than 44,978 employees indicated that prolonged sitting time without breaks at work is associated with an increased risk of self-reported overall poor health and back/neck pain, important components of physical health, which can impact the quality of life by reducing well-being [60].
In our analysis, transport-related SB was associated with a reduction in PWB in adults, even though they spent less time commuting (≅21 min/day) than younger adults. Previous studies have explored the relationship between time spent commuting while sedentary and several measures of life satisfaction in workers (satisfaction with work, home, personal life and leisure time) and reported a negative effect of commuting on all variables above, especially for workers with lower income who live in areas of high population density [61] and thus are more exposed to traffic jams. In this case, in addition to being exposed to the negative effects of SB “per se”, the added stress of lack of control over time and the transfer of time with family and friends or other activities could reduce PWB, according to resource drain theory (i.e., the transfer of finite personal resources, such as time, attention, and energy, from one domain to another) [62].
It should be noted that leisure-time SB was not related to any of the measures of well-being and quality of life in our investigation, possibly because adults in our sample may be less likely to be involved in the situations mentioned in topic 4.1, which leads younger adults to have worse PWB. In addition, what may contribute to this nonrelation is the fact that our sample of adults spent significantly less time in leisure time compared to young adults (170 min/week versus 269 min/week, respectively).