Social relationships and biological responses to loneliness

To truly understand how deeply rooted sociality is in our biology, we must take a step back and observe the evolution of the human brain. What clearly emerges is that our nervous system did not develop simply to solve technical or environmental problems, but primarily to manage relationships. In other words, the human brain is, first and foremost, a social brain.

The social brain hypothesis represents one of the most robust models in evolutionary biology for explaining the expansion of the brain in primates and humans. According to this perspective, the increase in the size of the neocortex was not driven primarily by needs related to the physical environment, but by the complex demands of group life (Dunbar, 2024) [8]. Living in a stable community involves a series of cognitive challenges: recognizing different individuals, remembering relationships, interpreting intentions, predicting behaviors, and maintaining often delicate social balances. All of this requires an extremely sophisticated processing capacity.

This relationship between the brain and sociality emerges even more clearly when observing the size of human groups. Comparative studies have shown that there is an extremely robust correlation between the size of the neocortex and the number of social relationships an individual is able to manage. In humans, this limit is around 150 individuals, a value known as “Dunbar’s number” (Dunbar, 2024) [8]. This figure is not random: it represents the equilibrium point between available cognitive capacities and the energy cost required to maintain stable relationships.

If we imagine the mind as a sort of “relationship manager,” we can better understand this concept. Every relationship requires time, attention, memory, and emotional energy. It is therefore not possible to maintain an infinite number of meaningful bonds: the brain imposes a natural limit, which is reflected in the structure of human social networks, organized into concentric circles of varying intensity.

The importance of sociality in brain development is not exclusive to humans, but also emerges clearly when comparing different species. Comparative studies among vertebrates show that, in primates, brain size is closely linked not only to the number of individuals in the group, but above all to the quality and stability of social relationships (Shultz and Dunbar, 2007) [9]. Maintaining lasting bonds, cooperating, negotiating, and resolving conflicts represents a much more complex cognitive challenge than simple individual survival.

A particularly interesting element is that the evolution of sociality seems to have occurred through progressive phases. In many species, the increase in cognitive capacity is initially linked to the management of pair bonds, which require mutual monitoring, coordination, and trust. In primates, this system then extended to larger groups, giving rise to increasingly complex social structures (Shultz and Dunbar, 2007) [9]. This transition represents one of the key moments in the evolution of the social brain.

In humans, this process has reached an unprecedented level of integration. Our species does not just live in groups, but builds actual highly coordinated social networks based on cooperation, communication, and knowledge sharing. This concept has been described as a “socio-cognitive niche,” a system in which cognitive capacities and social structures mutually reinforce each other (Whiten and Erdal, 2012) [10]. In this perspective, the human brain is not simply an individual tool, but part of a collective system, in which each individual contributes to the functioning of the group.

Theory of mind, which is the ability to understand the thoughts, emotions, and intentions of others, represents one of the pillars of this system. It allows for predicting the behavior of others, coordinating actions, and building relationships based on trust. Alongside this capacity, language allows for the precise transmission of information, while culture allows for the accumulation and sharing of knowledge over time (Whiten and Erdal, 2012) [10]. These elements, together with cooperation and egalitarianism, form an integrated system that has guided the evolution of the human species.

At the neurobiological level, these social functions are supported by a network of specific brain structures. Among these, the prefrontal cortex, the amygdala, and the temporoparietal junction play a central role in mentalization processes and relationship management. These areas allow for the interpretation of social signals, the evaluation of others' intentions, and the flexible adaptation of one's own behavior (Dunbar, 2024) [8].

A particularly significant finding emerges from neuroimaging studies (techniques used to visualize and study the brain): the size and structure of these brain areas are directly correlated with the complexity of an individual's social network. In particular, it has been observed that people with larger and more integrated social networks show a greater volume of gray matter in key regions of the social brain, such as the orbitofrontal cortex and the dorsomedial prefrontal cortex. This suggests that the ability to build and maintain relationships is not just a learned skill, but reflects a true structural organization of the brain (Kwak et al., 2018) [11].

An interesting aspect of these results is that it is not only how many relationships a person perceives they have that counts, but also how much they are recognized by others as a central node of the social network. Being “seen” by others as a relational point of reference is, in fact, associated with greater development of the brain areas involved in social understanding. This reinforces the idea that sociality is a deeply interactive phenomenon, which emerges from the encounter between individuals and not from subjective perception alone (Kwak et al., 2018) [11].

Overall, the human brain therefore appears to be shaped by the need to live in relationship. Every interaction, every bond, and every social dynamic contributes to shaping our cognitive and biological structures. Sociality is not an addition to our nature, but one of its fundamental components. Understanding this aspect means recognizing that human beings are not designed for isolation: on the contrary, they are built to connect.

If the human brain evolved to manage relationships, social behavior represents its concrete expression in the real world. This is not simply about "being together," but rather a set of highly sophisticated dynamics that have allowed our species to survive, adapt, and thrive in often unpredictable contexts. By observing human societies closest to ancestral ones, it becomes clear that sociality was not an option, but a biological necessity.

One of the most surprising aspects concerns how humans learn from the very first years of life. In hunter-gatherer societies, learning is not confined to formal or structured moments but occurs continuously through social interaction. Children, even in their first months of life, begin to internalize behaviors, values, and skills by observing others, imitating them, and actively participating in the life of the group (Hewlett et al., 2011) [12]. This process is extremely early and rapid: many of the fundamental skills for survival are acquired within the first few years of life.

What makes this system particularly effective is its distributed nature. Learning does not happen only from parents, but from an entire social network that includes peers, other adults, and members of the community. This multi-level cultural transmission—vertical, horizontal, and oblique—allows for the rapid and flexible dissemination of information. In this context, trust and autonomy play a central role: children are not mere passive recipients but participate actively, exploring and learning through play and direct experience (Hewlett et al., 2011) [12].

Alongside learning, another pillar of human social behavior is cooperation. Unlike many other species, humans cooperate on a large scale even with unrelated individuals. This aspect emerges particularly clearly when analyzing the social structure of hunter-gatherer populations: studies conducted on various communities show that groups are composed primarily of non-consanguineous individuals, with low genetic correlation among members (Hill et al., 2011) [13]. This finding is fundamental because it indicates that human cooperation cannot be explained solely by the logic of kinship but is based on broader and more complex social networks.

These networks are characterized by remarkable flexibility. Individuals move between groups, form new connections, and maintain ties distributed across multiple levels. This structure fosters the exchange of information, cultural transmission, and innovation, creating a dynamic system in which the group functions as a collective organism. In this context, sociality becomes the means through which knowledge is built and transmitted (Hill et al., 2011) [13].

A concrete example of this interdependence emerges by observing the dynamics of food sharing. In ancestral societies, access to resources was not guaranteed: hunting and gathering were activities characterized by high variability and uncertainty. In this scenario, food sharing represented a fundamental strategy to reduce individual risk and ensure the survival of the group. Recent models show that the distribution of resources tends to organize into modular networks, in which individuals and families aggregate around central nodes, creating efficient cooperative systems (Plana et al., 2023) [14]. This type of organization is not random but emerges as an optimal solution in contexts of scarcity and unpredictability.

Sharing is therefore not just an altruistic act, but an adaptive strategy. Through it, the risk of hunger is distributed among the members of the group, transforming individual vulnerability into collective resilience. In other words, the group becomes a safety net.

This logic is also reflected in the multi-level structure of human societies. Studies conducted on contemporary hunter-gatherer populations show that social organization is articulated in different levels: the family, small sharing groups, and larger camps (Dyble et al., 2016) [15]. Each level performs a specific function. Within the family, cooperation based on the division of roles is observed; in sharing groups, mutual support among relatives emerges; at the broader community level, cooperation with unrelated individuals allows for coping with resource variability.

This multi-level structure represents one of the distinctive characteristics of human sociality. It allows for balancing close relationships and broader ties, ensuring both stability and flexibility. On one hand, more intimate relationships offer emotional support and security; on the other, more extensive networks increase opportunities for exchange, learning, and cooperation.

Overall, human social behavior appears as a highly integrated system, in which learning, cooperation, and sharing are continuously intertwined. Each individual does not act in isolation but within a network of relationships that profoundly influence their possibilities for survival and development.

This perspective allows us to understand a fundamental point: sociality is not simply an advantage, but a necessary condition for the functioning of the species. In the past, being isolated meant being exposed to high risk, not only from an emotional standpoint but especially in terms of survival. Connection with others was the primary tool for adapting to the environment.

Understanding these evolutionary dynamics helps to interpret the role of sociality in the modern context more deeply. What might seem like a psychological need today actually has its roots in biological and behavioral mechanisms built over thousands of years. Ultimately, the human being is not designed to live alone, but to exist within a network of relationships.

To fully understand the role of sociality in human history, it is necessary to look closely at the context in which our species lived for the majority of its existence: that of hunter-gatherers. For over 95% of our evolutionary history, humans did not live in cities, nor in structured societies as we know them today, but in dynamic, flexible, and deeply interconnected social systems. It is in this environment that the biological and behavioral mechanisms that still guide the way we relate to one another today were developed.

Contrary to the traditional image of small, isolated groups, the most recent evidence shows that hunter-gatherer societies were embedded in much broader and more complex social networks. Local groups, often small in size, represented only the visible part of a more extensive social structure, composed of relationships distributed across vast territories and maintained over time through exchange, mobility, and symbolic bonds. In this context, sociality was not confined to the immediate group but extended far beyond it, creating a continuous web of connections between individuals and communities.

This network-based organization emerges clearly when analyzing the composition of the groups. Ethnographic data indicate that local units were not composed primarily of close relatives, but of individuals from different backgrounds, often non-consanguineous (Bird et al., 2019) [16]. This implies that social cohesion was not based exclusively on genetics, but on systems of relationships built, maintained, and activated over time. True "wealth" was not represented by material accumulation, but by the ability to build and maintain social bonds: a genuine form of relational wealth.

Another fundamental element concerns the extraordinary variability of these societies. For a long time, it was believed that hunter-gatherers lived in small, nomadic, and rigidly egalitarian groups. However, archaeological and ethnographic evidence shows a much more complex picture. Some populations were highly mobile, others more sedentary; some showed an equitable distribution of resources, others forms of hierarchy and more structured organization (Singh and Glowacki, 2022) [17]. This diversity suggests that human sociality does not follow a single model, but is the result of an extraordinary capacity for adaptation to environmental conditions.

This flexibility represents one of the key elements of human evolution. Humans did not adapt to a single type of social organization, but developed the ability to modify their relational structures based on the context. In rich and predictable environments, forms of sedentary life and larger aggregations could emerge; in more difficult contexts, mobility and more fluid organizations prevailed (Singh and Glowacki, 2022) [17]. In both cases, sociality remained the central factor that allowed for the management of resources, risks, and opportunities.

A particularly fascinating aspect concerns the geographical extent of social networks. Archaeological analyses based on strontium isotopes have shown that, as early as 30,000 years ago, there were exchange systems that connected groups hundreds of kilometers apart (Stewart et al., 2020) [18]. Symbolic objects, such as ostrich eggshell beads, were transported and traded over long distances, serving as true "social markers" and tools for connection between groups.

These networks did not just have a cultural function; they represented a survival strategy. Connecting groups located in ecologically diverse environments allowed for the reduction of risks associated with resource variability. In the event of local scarcity, the social network offered access to alternative territories and resources, increasing the overall resilience of the system. In other words, sociality functioned as a form of biological insurance against environmental uncertainty (Stewart et al., 2020) [18].

This model highlights a fundamental principle: in the past, surviving meant being connected. The isolated individual was exposed to high risks, while the individual embedded in a broad and active social network had a greater probability of adapting and thriving. Large-scale cooperation, mobility, and the ability to maintain relationships even at a distance represented decisive evolutionary advantages.

Overall, the image that emerges is that of a deeply interdependent species, in which sociality was not an accessory element, but the supporting structure of our biological and behavioral organization. Hunter-gatherers did not simply live in groups: they lived within networks.

Understanding this reality means redefining the very concept of human nature. Humans are not designed for self-sufficiency, but for interdependence. The ability to build, maintain, and activate relationships represents not only an evolutionary advantage but one of the distinctive traits of our species.

When analyzing the role of sociality in human health, one of the most relevant and, at the same time, most impactful aspects concerns its direct relationship with mortality. It is no longer just a matter of understanding whether relationships influence well-being or the risk of disease, but of observing how their presence or absence can concretely affect the very probability of survival.

The most robust epidemiological evidence shows that social isolation is a major predictor of all-cause mortality. A large prospective cohort, including 580,182 adults enrolled in the Cancer Prevention Study II, highlighted a significant association between increasing social isolation and the risk of death. Comparing the most isolated individuals with the least isolated, the risk of all-cause mortality was more than doubled in Black men (HR=2.34) and Black women (HR=2.13), while it increased by 60% in White men and 84% in White women; the association with all-cause mortality therefore emerged in all groups analyzed, with no statistically significant differences between men and women. The link did not only concern overall mortality: social isolation was also associated with higher cardiovascular mortality in each subgroup. Overall, these results reinforce the hypothesis that the relational dimension represents a significant determinant of health and longevity, capable of exerting its influence in populations that differ by sex and ethnic background (Alcaraz et al., 2019) [25].

A particularly significant aspect is that this increase in risk does not only concern general mortality, but extends to specific causes, particularly cardiovascular ones. Prospective studies have shown that socially isolated individuals have an almost doubled risk of cardiovascular mortality, as well as an increased incidence of events such as stroke (Kawachi et al., 1996) [26]. This data suggests that sociality does not act only at a behavioral level, but intervenes directly in the pathophysiological mechanisms that regulate cardiovascular function.

The strength of this association emerges with even greater clarity when analyzing clinical populations. In patients with coronary artery disease, social isolation is associated with a significant increase in the risk of death, both from cardiac causes and from all causes, with values more than double those of non-isolated subjects (Brummett et al., 2001) [27]. This result is particularly relevant because it persists even after controlling for disease severity and other risk factors, indicating that the social dimension directly influences clinical prognosis.

A key element that emerges from these studies is that it is not only the presence of relationships that counts, but also their quality. Socially isolated patients do not necessarily perceive a reduction in the number of contacts, but rather a lower quality of the social support received. This suggests that the benefit of sociality does not derive simply from the quantity of interactions, but from their ability to provide emotional support, security, and stress regulation.

Even at the general population level, data confirm a clear and consistent relationship between social isolation and mortality. Cohort studies conducted in different contexts show that the most isolated subjects have an increased risk of death of between 40% and 70%, with a continuous gradient: the higher the level of isolation, the higher the risk (Laugesen et al., 2018) [28]. This trend suggests a dose-response effect, in which the progressive reduction of social relationships translates into a proportional increase in biological vulnerability.

A further element of great interest concerns the temporal dimension. It is not only the presence of social isolation or loneliness that is associated with health outcomes, but also their persistence over time. A prospective study conducted on 18,258 participants of the UK Biobank, aged between 38 and 73, distinguished four different conditions: absence, transient exposure, onset over time, and persistent exposure. During a median follow-up of 8 years, persistent social isolation, compared to its absence, was associated with a 42% increase in all-cause mortality and a 53% increase in cardiovascular mortality. A similar trend was observed for persistent loneliness, associated with increases of 28% and 52%, respectively. The analysis was not limited to clinical events: in a subgroup of 5,188 participants who underwent cardiovascular magnetic resonance imaging, the persistence and accumulation of these social conditions were also associated with worse cardiac function. These results therefore suggest that the duration of exposure represents an important component of the relationship between social relationships and health: occasional or transient conditions do not seem equivalent to a situation of isolation or loneliness maintained over the years (Chen et al., 2024) [29].

This concept is further reinforced by long-term studies on general populations, which highlight how persistent loneliness is associated with an increase in mortality of up to 57%, while social isolation entails a significant, albeit slightly lower, increase (Crowe et al., 2021) [30]. The difference between these two dimensions suggests that the subjective experience of disconnection may have an even deeper impact than the simple objective lack of relationships.

Even in the most socioeconomically advanced contexts, where welfare systems guarantee high levels of healthcare, the relationship between social isolation and mortality remains significant. This data is particularly important because it indicates that the relational dimension operates through biological and behavioral mechanisms that cannot be completely compensated for by external factors (Laugesen et al., 2018) [28].

Finally, it is relevant to observe that the impact of social isolation on mortality does not exclusively concern older age groups, but also emerges in younger adults. The Tromsø Study, conducted in Norway on 17,796 participants aged between 25 and 69 with a follow-up extended to 2023, highlighted a significant association between social isolation, loneliness, and all-cause mortality. During the observation, 3,729 deaths were recorded; the most isolated women had a 37% higher mortality risk compared to the least isolated, while in men the increase reached 41%. A particularly interesting fact emerges when considering age: in participants who were under 50 at baseline, the association was even more marked, with a 55% increase in risk in women and 76% in men. Loneliness also showed an independent association with mortality, with a 51% higher risk in women and 46% in men. The study also highlights the possible persistence of these conditions over time: a substantial portion of the most isolated participants continued to be so in subsequent surveys (Løvsletten and Brenn, 2024) [31].

Overall, an extremely clear picture emerges: sociality is not just an element of well-being, but a direct determinant of survival. Social relationships act as a biological regulation system, capable of influencing the functioning of the cardiovascular, immune, and neuroendocrine systems. Their absence, conversely, exposes the organism to a condition of systemic vulnerability, which over time can translate into a concrete increase in the risk of death.

Understanding this relationship means recognizing that health cannot be interpreted exclusively in individual terms. Human beings are biologically designed to live in relationships, and the quality of these relationships represents one of the most powerful factors in determining not only how we live, but also how long we live.

If social isolation is a powerful risk factor for mortality, the other side of the coin is the protective role of social relationships. Understanding this aspect means shifting the focus from a purely negative logic—what increases risk—to an active and constructive perspective: what reduces it. In this sense, sociality is not just a factor to be addressed when it is lacking, but a biological resource capable of positively modulating survival.

Longitudinal evidence clearly shows that individuals embedded in broader and more structured social networks have a higher probability of survival over time. In a cohort of elderly people followed for ten years, the presence of solid social relationships, particularly active and frequent friendships, was associated with a significant reduction in the risk of death, approximately 22% compared to more isolated subjects (Giles et al., 2005) [32]. This finding is particularly relevant because it emerges even after accounting for variables such as health status, functional conditions, and lifestyle, suggesting a direct effect of social relationships on longevity.

An interesting aspect concerns the type of relationships. Not all social connections produce the same effect. Friendships, for example, seem to have a more marked impact than family ties. This phenomenon can be interpreted by considering the nature of these relationships: friendships are generally based on choice, reciprocity, and sharing—elements that foster authentic emotional support and greater active participation in social life. Conversely, family ties, while fundamental, can be influenced by obligations or more complex dynamics that do not always translate into a direct health benefit (Giles et al., 2005) [32].

In parallel, other studies highlight how the protection associated with sociality does not depend exclusively on the number of relationships, but also on the structure of the social network and the role the individual occupies within it. A study conducted on 1,174 elderly people living in Leganés, Spain, followed for six years, showed that having a trusted person was associated with an approximately 25% reduction in mortality risk, regardless of various sociodemographic and health characteristics (Rodriguez-Laso et al., 2007) [33]. However, this finding does not seem to be simply attributable to the emotional support received: the latter, when considered separately, was not in fact associated with survival. What emerged more strongly were the structural and participatory aspects of social relationships. A lack of social participation was associated with a 50% higher mortality risk, while maintaining significant roles in the lives of those close to one was associated with greater survival. This introduces a particularly important dimension: the benefit of relationships does not seem to derive only from receiving support, but also from feeling involved, useful, and participating in the lives of others (Rodriguez-Laso et al., 2007) [33].

A particularly relevant aspect is that these protective effects persist even after considering clinical and functional factors. This means that sociality does not simply act as an indirect indicator of good health, but represents an independent determinant of survival. Even in the presence of comorbidities or conditions of frailty, maintaining active social relationships continues to offer a significant advantage.

Overall, a key concept emerges: sociality functions as a true "systemic protective factor." Social relationships act on multiple levels simultaneously: they modulate stress, influence behaviors, support adherence to treatments, and contribute to maintaining psychophysical balance. This integrated effect translates, in the long term, into a concrete reduction in mortality risk.

If sociality represents a direct determinant of health and survival, one of the most relevant aspects concerns its ability to influence other risk factors, particularly those related to lifestyle. Among these, nutrition plays a central role. What is emerging with increasing clarity from the literature is that the quality of one's diet does not depend solely on individual choices or nutritional knowledge, but is profoundly conditioned by the social context in which the individual lives.

Large-scale evidence shows that social isolation is systematically associated with less healthy eating behaviors. In an analysis conducted on over 67,000 European adults, socially isolated individuals showed a significantly higher probability of following an inadequate diet, characterized in particular by a reduced intake of fruits and vegetables (Delerue Matos et al., 2021) [34]. This finding is not isolated, but emerges consistently across numerous geographical contexts, suggesting a stable and reproducible pattern.

The relationship between sociality and nutrition appears even more evident when analyzing the nutritional quality of the diet. Studies indicate that social isolation is associated with a significant increase in the risk of deficiencies in essential micronutrients, including magnesium, potassium, vitamin B6, folates, and vitamin C. These are fundamental nutrients for the proper functioning of the immune system, as well as the cardiovascular and metabolic systems. Their deficiency therefore represents a possible mechanism through which social isolation contributes to the development of chronic diseases (Steptoe et al., 2024) [35].

A particularly interesting element is that this association mainly concerns the objective dimension of sociality—that is, isolation—rather than the subjective perception of loneliness. In other words, it is not just feeling lonely that influences diet, but above all living in a condition of poor social integration (Steptoe et al., 2024) [35]. This suggests that concrete factors, such as the lack of practical support or shared contexts, play a decisive role.

In support of this interpretation, studies show that socially isolated individuals are less likely to maintain healthy eating behaviors over time, including the adequate consumption of fruits and vegetables (Kobayashi & Steptoe, 2018) [36]. This data highlights how sociality does not only influence episodic choices, but contributes to structuring stable eating habits in the long term.

The relationship between isolation and nutrition is not limited to nutritional quality, but also involves the ways in which food is consumed. A systematic review of the literature highlights that loneliness and isolation are associated with a reduction in the overall quality of the diet, a lower consumption of fresh foods, and a greater reliance on energy-dense foods (Hanna et al., 2023) [37]. In this context, the meal loses its social dimension and becomes a functional act or, in some cases, a mechanism of emotional compensation.

The concept of commensality, or eating together, emerges as a key element for understanding this phenomenon. A shared meal represents not just a nutritional moment, but a relational experience that structures eating behavior. Its absence can translate into less regular meals, reduced dietary variety, and less motivation to prepare balanced meals (Hanna et al., 2023) [37].

A further element to consider is that social isolation is frequently associated with other unhealthy behaviors, creating a cumulative effect. Studies on general populations show that isolated individuals simultaneously present a higher probability of an unhealthy diet, physical inactivity, and other risk factors (Hämmig, 2019) [24]. This suggests that sociality does not act on a single behavior, but influences the entire lifestyle.

From a physiological and behavioral point of view, several mechanisms can explain these associations. Firstly, the lack of social integration reduces exposure to healthy norms and behavioral models, limiting the so-called “social control” that often guides daily choices (Delerue Matos et al., 2021) [34]. Secondly, the absence of practical support can make it more difficult to access quality food or prepare meals. Finally, the reduction of opportunities for sharing limits the chances of structuring regular eating behaviors.

Overall, an integrated vision emerges: nutrition is not an isolated behavior, but a profoundly social phenomenon. Nutritional choices are influenced by relationships, contexts, and interaction dynamics that go well beyond the individual dimension.

Understanding this connection means recognizing that intervening in nutrition without considering sociality risks being partial. Improving the quality of the diet does not just mean providing nutritional guidance, but also creating favorable social conditions: relationships, shared contexts, support, and integration.

In this perspective, sociality becomes an indirect but powerful determinant of nutrition, capable of guiding daily behaviors and, through them, profoundly influencing metabolic risk and long-term health.

If nutrition represents one of the main areas in which sociality exerts an indirect but profound influence, smoking constitutes an even clearer example of how risky behaviors can be shaped by the relational context. Unlike diet, which is often perceived as a daily choice linked to knowledge and the availability of food, tobacco consumption fits into a more complex dimension, in which emotional, social, and neurobiological factors are tightly intertwined.

Epidemiological evidence clearly shows that social isolation is associated with a higher probability of smoking. In a representative population of over 8,000 elderly individuals, socially isolated people are more than twice as likely to be smokers, with an increase that becomes more than fivefold in cases of severe isolation (Gimm et al., 2023) [38]. This data suggests a particularly marked dose-response effect: as isolation increases, the risk of adopting this behavior increases proportionally.

This link is not limited to the presence or absence of the behavior, but also extends to its intensity. These studies indicate that higher levels of loneliness are associated with a significant increase in the number of cigarettes smoked daily (Yang et al., 2022) [39]. In other words, not only are more isolated people more likely to be smokers, but they also tend to smoke more, further amplifying the risk.

A particularly interesting aspect concerns the role of behaviors as mediators between social isolation and mortality. In patients with stable ischemic heart disease, smoking emerges as one of the main factors through which low social integration translates into an increased risk of death (Kreibig et al., 2014) [40]. This finding is of great relevance because it indicates that sociality does not act only directly on physiology, but also indirectly, by modulating behaviors that have a concrete impact on survival.

To understand this relationship, it is useful to consider the underlying mechanisms. One of the most relevant is the function of smoking as a coping strategy (a behavior or thought used to manage stress and adapt to difficulties). In conditions of isolation, characterized by greater stress, boredom, and emotional distress, nicotine consumption can become a tool for self-regulation, used to modulate negative internal states (Gimm et al., 2023) [38]. This explains why isolation is often also associated with higher levels of anxiety and depression, which in turn favor the maintenance of the behavior.

Alongside this, a second mechanism emerges related to the reduction of social control. In the presence of active relationships, individual behaviors are often influenced, more or less explicitly, by shared norms, expectations, and feedback from others. The absence of this regulatory system can facilitate the adoption and maintenance of risky behaviors, such as smoking (Gimm et al., 2023) [38]. In other words, when the social context is missing, one of the main behavioral brakes also disappears.

A further element concerns the possible bidirectionality of the relationship. Smoking, in fact, can in turn contribute to social isolation, both for reasons related to stigma and for the progressive reduction of interactions in contexts where tobacco consumption is limited or socially discouraged. This creates a vicious cycle in which isolation and smoking reinforce each other, making it more difficult to stop the behavior (Gimm et al., 2023) [38].

At a deeper level, experimental studies also suggest a neurobiological basis for this association. Animal models show that social isolation is capable of altering reward systems, increasing sensitivity to stimuli associated with nicotine and facilitating relapse (Mastrogiovanni et al., 2021) [41]. In these conditions, it is not so much the substance itself that changes, but the way the brain responds to the stimuli that trigger it, making the behavior more automatic and difficult to control.

This increased vulnerability also emerges clearly in real-world contexts. During periods of forced isolation, such as the lockdown linked to the SARS-CoV-2 pandemic, a significant portion of smokers increased their cigarette consumption, with relevant average increases (Ferrante et al., 2020) [42]. This data confirms how the reduction of social interactions can quickly translate into a worsening of health behaviors.

Overall, the picture that emerges is consistent and multidimensional. Sociality acts as a regulatory factor for behavior: when it is present, it helps to limit the adoption of risky behaviors; when it is lacking, it leaves room for dynamics that favor the establishment and maintenance of addiction.

Understanding this relationship means recognizing that smoking is not simply an individual choice or an isolated addiction, but a behavior deeply influenced by the social context. Intervening exclusively on the individual behavior, without considering the relational dimension, therefore risks being insufficient.

In this perspective, sociality becomes a key element also in smoking prevention and cessation strategies. Strengthening social networks, promoting integration, and reducing isolation does not only represent an intervention on psychological well-being, but a concrete lever to modify behaviors that directly affect health and survival.

A further area, often less visible but equally crucial, concerns adherence to pharmacological therapy. In this case, the problem is not so much the adoption of a harmful behavior, but rather the failure to perform a protective one. Yet, the consequences can be just as significant, especially in individuals suffering from chronic conditions.

Evidence consistently shows that social isolation is associated with a significant reduction in treatment adherence. In large populations of elderly people with chronic diseases, socially isolated individuals are more likely to fail to follow medication prescriptions correctly, thereby compromising the effectiveness of treatments (Lu et al., 2020) [43]. This finding is particularly relevant because it concerns a central dimension of modern medicine: the ability to translate a prescribed therapy into a real benefit for the patient.

The relationship between sociality and adherence is not direct and linear, however, but mediated by a series of psychosocial factors. Among these, social support emerges as a key element. Studies based on mediation models demonstrate that social isolation reduces the availability of emotional, informational, and practical support, and that this reduction represents the main mechanism through which non-adherence occurs (Lu et al., 2020) [43]. In other words, it is not simply isolation itself that causes the problem, but what is missing when relationships diminish.

This dynamic has also been confirmed by several studies, which show how social isolation increases loneliness over time and progressively reduces social support, with a negative cumulative effect on treatment adherence (Yu et al., 2024) [44]. This trend suggests that the problem is not static, but evolves over time, becoming increasingly relevant as isolation progresses.

Alongside social support, loneliness represents another critical factor. Unlike isolation, which describes an objective condition, loneliness reflects a subjective perception of disconnection. Recent studies indicate that high levels of loneliness are associated with a reduction in long-term adherence, with effects that become evident especially after months or years (Fan et al., 2024) [45]. This suggests that the emotional dimension of sociality can progressively influence the motivation and ability to follow a therapy.

A particularly interesting element concerns the role of self-efficacy, that is, the perception of being able to correctly manage one's own treatment. Studies on hypertensive patients show that loneliness is associated with a reduction in self-efficacy, while social support increases it (Hacihasanoglu Asilar et al., 2020) [46]. This data is fundamental because treatment adherence depends not only on understanding medical instructions but also on the patient's confidence in their ability to apply them in daily life.

In this context, social support performs a multiple function. On one hand, it provides practical help, reminders, assistance in managing medications, and accompaniment to medical appointments. On the other, it offers emotional support that reduces stress and increases motivation. This dual function makes social networks one of the most important determinants of treatment adherence (Improta et al., 2026) [47].

A further aspect to consider is that non-adherence is not an isolated phenomenon, but often fits into a broader framework of unfavorable health behaviors. As already observed for smoking and diet, in this case too, social isolation tends to generate a cumulative effect, in which different risk factors reinforce each other. This makes clinical management particularly complex, especially in patients with multimorbidity.

Overall, a key concept emerges: pharmacological therapy is not a purely individual act, but a behavior deeply influenced by the social context. Following a therapy requires organization, motivation, support, and continuity—all dimensions that are facilitated or hindered by the quality of one's relationships.

Understanding this relationship means redefining the very concept of adherence. It is not simply about "taking medications correctly," but about being embedded in a system that makes this behavior possible over time. In the absence of such a system, even the best therapy risks losing its effectiveness. From this perspective, sociality becomes an integral component of the therapeutic journey. Intervening on adherence therefore means not only educating the patient, but also strengthening their relational networks, reducing isolation, and promoting a context in which care can be truly sustained.

While diet, smoking, and treatment adherence are areas where sociality modulates complex behaviors, physical activity is arguably the most immediate and visible expression of this influence. Movement, in fact, is not merely a biological function but a behavior deeply integrated into the social context: it often arises from opportunities for interaction, sharing, and participation. When these dimensions are lacking, activity levels also tend to decrease significantly.

Evidence consistently shows that social isolation is associated with a decrease in physical activity and an increase in sedentary behavior. Studies based on objective measurements using accelerometers highlight that socially isolated individuals exhibit significantly lower levels of total physical activity and spend more time in sedentary conditions, regardless of factors such as age, health status, or socioeconomic conditions (Schrempft et al., 2019) [48]. This finding is particularly relevant because it indicates a direct effect of sociality on motor behavior, not mediated solely by clinical conditions or functional limitations.

An interesting aspect concerns the distinction between social isolation and loneliness. While the former, understood as an objective condition of a reduced relational network, shows a clear association with reduced physical activity, perceived loneliness does not always present the same relationship (Schrempft et al., 2019) [48]. This suggests that the concrete presence of relationships and social contexts acts as a direct stimulus for movement, regardless of subjective perception.

However, when analyzing the longitudinal dimension, the role of loneliness as a predictive factor also emerges. Prospective studies demonstrate that individuals who experience higher levels of loneliness have a significantly lower probability of engaging in physical activity in subsequent years and a greater tendency to become sedentary (Hawkley et al., 2009) [49]. This data highlights how the emotional dimension of social disconnection can progressively influence behavior, reducing motivation and the ability to maintain an active lifestyle.

Alongside these data, the protective role of social well-being emerges strongly. Higher levels of social support and active participation in community life are associated with a significant reduction in time spent in sedentary activities and an increase in physical activity levels, even of a light nature (Chen et al., 2021) [51]. This effect is particularly evident in older age groups, suggesting that, as age increases, sociality becomes an increasingly decisive factor in maintaining an active lifestyle.

This relationship also emerges transversally in younger populations. Studies conducted on university students show that high levels of loneliness are associated with a greater probability of physical inactivity and a higher presence of sedentary behaviors (Jiang et al., 2024) [50]. This suggests that the influence of sociality on physical activity is not limited to older age but is distributed throughout the entire life cycle.

To understand these results, it is useful to consider the underlying mechanisms. On one hand, sociality creates concrete opportunities for movement: going out, meeting up, and participating in group activities inevitably imply an increase in physical activity. On the other hand, it acts at a motivational and emotional level. The presence of relationships fosters the sharing of goals, mutual support, and the continuity of behaviors over time.

A particularly relevant element concerns the role of emotional regulation. Supporting studies indicate that loneliness can reduce the ability to modulate emotional states, making it more difficult to maintain healthy behaviors such as physical activity (Hawkley et al., 2009) [49]. In this context, movement loses its dimension of gratification and becomes more difficult to sustain over time.

Overall, a coherent picture emerges: sociality not only facilitates physical activity but represents one of its main determinants. Its absence, conversely, promotes inactivity and sedentary behavior, two conditions closely associated with an increased metabolic, cardiovascular, and systemic risk. Understanding this relationship means recognizing that promoting physical activity cannot be limited to individual recommendations or structured programs. It is necessary to intervene in the social context as well, creating conditions that foster participation, integration, and sharing.

In this perspective, movement is not just a biological behavior but a social phenomenon. And, as such, it depends largely on the quality of the relationships that surround the individual.