As I discussed in my last essay, social relationships – the types, the numbers, and the nature – constitute a major risk factor for health. It rivals well established medical risk factors such as hypertension, hyperlipidemia, obesity, and physical fitness. In fact, by one estimate nearly 60% of the variation in health outcomes is caused by social determinants of health. However, causes and effects for these diseases are neither linear nor sequential. They are better represented by a web-like interplay with complex feedback loops ranging across systems. The systems above (social and environmental) interacting with the systems below (psychological, physiological, and genetic) causing disease through direct and indirect pathways. A wide variety of research has linked social isolation to a variety of disease-relevant physiological responses including cardiovascular reactivity, endocrine response, and suppressed immune function. Network structures and processes are implicated in a variety of psychosocial mechanisms as well as behavioral and biological pathways, which in turn, influences disease onset, trajectories, and outcomes. Therefore, any explanatory or predictive model of chronic diseases must include these social factors.
Two models that attempt to connect the systems above (social and the environmental) to the systems below (psychophysiological) are the social baseline theory and polyvagal theory (next essay). The social baseline theory states that the default state for the brain is one that is networked. The brain expects access to relationships characterized by “interdependence, shared goals, and joint attention.” This connectivity leads to features such as load sharing and risk distribution where effort and risk is distributed across networked brains. The brain expects other brains to help assess risk and carry the cognitive load that environments present. Furthermore, any move away from this default state is interpreted as an environment of resource constraint and leads to a psychophysiological state of increased cognitive and physiological effort. If you link this model to the observation that a likelihood of an action is the function of its perceived metabolic cost against its anticipated payoff in the context of available resources, then you can predict the likelihood of a certain behavior. Metabolically costly behaviors leading to low rewards are unlikely to be performed. Similarly, when in low energy states such as illness or fatigue the likelihood of an action also decreases. The brain interprets and considers being alone as equivalent to being in a low energy state and actions become less likely. As empirical evidence shows, hills appear steeper, distances, further, and threats more threatening when fatigued, tired, physically fit, and alone.
Perceptions of social isolation – loneliness – deleteriously influence physiological functioning such as increased blood pressure and diminished sleep quality leading to increased premature morbidity and mortality. These effects are largely mediated by the neuroendocrine hypothalamic-pituitary adrenocortical (HPA) axis. This axis controls reactions to stress and regulates many body processes including digestion, the immune system, mood, and energy storage and expenditure via feedback loops at many levels including at the level of gene transcription. Thus the pernicious effects of the system above – social isolation – propagate directly to the system below – HPA axis – and indirectly below to the level of gene expression, leading to phenotypes such as cardiovascular disease (hypertension and coronary heart disease), endocrine disorders (diabetes), and diseases of impaired immunity.
In our age of connectivity where time and space have seemingly condensed exponentially since the onset of the Industrial Revolution, social isolation might not seem prevalent. Nonetheless, despite the increased connectivity it has been shown that the quantity and quality of social relationships in industrialized societies have decreased. For example, in the last 20 years, there has been a 3-fold increase in Americans who report having no confidant. Factors such as reduced intergenerational living, greater social mobility, delayed marriage, dual-career families, increased single-residence households, and increased age-related disabilities have been theorized as to play a role in social isolation. The process of Industrialization has affected the quality of our relationships and has come with a cost (increased prevalence of chronic diseases and the accompanying morbidity and mortality) that connectivity has not been able to alleviate. A clear example of the systems above interacting with the systems below to affect the system in between; our health.