Rationale:

Ageing, Social science and allostatic load

Many physiological systems are proposed as the mediators that allow social processes to "get under the skin". Allostatic load is conceptualised as the 'wear and tear' associated with the response to chronic or repeated stress (Mcewen and Stellar 1993). The concept has been adopted in many analyses of the association of the social environment with health as it represents the impact on a multiple physiological systems including 'primary' stress pathways and secondary 'intermediate' pathways (Seeman et al., 2001). A number of studies within CLOSER and others that have detailed measures of the social environment have used the concept of allostatic load to examine social, psychological and other exposures (Babosa-Solis et al., 2015, Read & Grundy, 2015; Rod et al., 2015; Robertson et al., 2015). Allostatic load is generally measured through a composite index of indicators that reflect this multi-system approach and include neuroendocrine, metabolic, immune and cardiovascular markers. However operationalisation of allostatic load varies across surveys as it is limited to the availability of biomarkers within studies. Consequently, it is difficult to compare analyses across cohorts. While there are a few studies in younger age groups (Brody et al., 2014), studies that have examined allostatic load are generally conducted in older age groups (Seeman et al., 2010; Gruenwald et al., 2012; Read and Grundy, 2014). It is unclear that the allostatic load construct remains stable by age or by other factors such as medication status (Booth et al., 2014). A number of studies have suggested that allostatic load varies by social position (Seeman et al., 2010; Gruenwald et al., 2012). Again a majority of these studies are conducted in older age groups and, while one suggests that social differences in allostatic load are apparent in those aged under 75 y only (Robertson et al., 2014), further work is required to understand when in the lifespan the association of allostatic load with measures of social position emerges.

Plan of analyses

1)We will catalogue the biomarkers in the component studies within CLOSER and other studies such as Whitehall II, Twenty-07 and ELSA. In doing this we will highlight valuable analytes for social-biological research, and provide guidance on the key issues that need to be considered in their analysis.

2) We would scope the literature to examine which biological markers are typically included in the construction of Allostatic load. Examine which of the identified markers have been collected across the CLOSER studies with a focus on categorising them as components of primary or intermediate and markers. We will then examine how the inclusion/exclusion of typical plus additional markers might affect our understanding of the construct and its social patterning.

Finally we propose three substantive research questions:

1)to operationalise 'allostatic load' across the cohorts with varying inclusion criteria and by medication status.

2)to capitalise on the on-going work package in CLOSER, which has harmonised measures of social position across the CLOSER studies and examine how social position is related to 'Allostatic load'.

3)to capitalise on the wide age range available in with CLOSER studies to examine how allostatic load evolves across the age span.