Similarly, psychosocial factors such as stress and adverse life events have been found to relate to higher cortisol concentrations in some( Gerritsen et al., 2010) but not all studies ( Ockenburg et al., 2015). For example, some studies have found that health-impacting behaviours such as physical activity are related to sex hormones (eg, lower testosterone among women), ( Rinaldi et al., 2014) while other studies have reported null associations ( Sowers et al., 2001). In addition to potential causal roles in affecting some health outcomes, understanding the links between SEP and hormones could help to identify if some population groups may be especially vulnerable to unwarranted pharmacological hormone supplementation (eg, of testosterone among older men( Gan et al., 2013)).īoth material and psychosocial explanations for health inequalities ( Bartley, 2008) could potentially be partly mediated by endocrine function, although the robustness of the links between hormones and material and psychosocial factors are uncertain. While there is consistent evidence from trials in hypogonadal men that testosterone administration leads to gains in muscle and/or losses in fat mass ( Isidori et al., 2005), and revitalised sexual function ( Corona et al., 2014), a causal effect of endogenous testosterone on cardiovascular disease risk was not supported by a recent Mendelian randomisation study ( Haring et al., 2013). Not all observational studies have found expected associations between hormones such as IGF-I or cortisol and health-related outcomes ( Singh-Manoux et al., 2014, Stenholm et al., 2010).
The causal nature of hormone and health outcome relationships is not well-established and may differ by outcome given the multiple actions of hormones on different sites of the body.
SEP may be related to an adverse hormone profile across multiple axes, which may have additive and/or synergistic effects on physical and cognitive function in old age ( Cappola et al., 2009, Hertoghie, 2005). Differences in endocrine function, and in rates of age-related changes, could therefore partly underlie socioeconomic inequalities in health and function. For example, circulating IGF-I and testosterone are thought to decline with age, while cortisol concentrations may be higher at older ages ( Bann et al., 2014b, Bann et al., 2015, Chahal and Drake, 2007, Kaufman and Vermeulen, 2005). The endocrine system may be especially important at older ages-changes in both its regulation and hormone production have been hypothesised to be key potential mechanisms underlying the ageing process and its adverse consequences ( Chahal and Drake, 2007, Ferrucci and Studenski, 2012, Hertoghie, 2005). Cortisol measures (including a blunted ‘diurnal drop’) have also been associated with worse physical function ( Gardner et al., 2013). Low IGF-I has been related to worse physical and cognitive function, and both high and low IGF-I associated with increased risk of cancer and cardiovascular mortality ( Birnie et al., 2012, Burgers et al., 2011, Westwood et al., 2014). For example, low testosterone has been associated with adverse health outcomes among men, and high testosterone has been linked to adverse outcomes among women. The endocrine system, as assessed by circulating hormone concentrations in multiple axes, is influenced by environmental factors operating in both early and adult life, and has important roles in regulating both early life development and adult health and function ( Ben-Shlomo et al., 2005, Cappola et al., 2007, Parekh et al., 2010). However, less is known about the biological mechanisms which underlie these inequalities that is, how exposure to socioeconomic conditions in both early and adult life become embodied, leading to pathophysiological changes, impairment, disability and disease ( Hertzman, 1999, Shonkoff et al., 2009). Socioeconomic inequalities in premature mortality, as well as physical and cognitive function are known to be substantial in the UK and many other developed nations ( Hurst et al., 2013, Mackenbach et al., 2014, Schoeni et al., 2005).