Exploiting the existing biomarker data available in CLOSER: social position, age and allostatic load

Background

The UK is home to the world’s largest and longest-running longitudinal studies. CLOSER (Cohort & Longitudinal Studies Enhancement Resources), brings together eight leading studies, the British Library and the UK Data Service, and aims to maximise their use, value and impact both at home and abroad.

This project aims to create a catalogue of biomarkers and bio measures data available in CLOSER and other longitudinal studies, as well as to describe, compare and analyse that data with the objective of measuring Allostatic Load (AL), a quantification of cumulative stress on the body.

At present, there is no agreement on the methodology to measure AL and no consensus exists as to what biomarkers are essential to calculate AL. The researchers will use past definitions and methods from the literature to calculate AL using the available biomarkers in each of the component CLOSER studies and others, thus comparing and assessing the usefulness of each definition/methodology. This process will help to develop a gold standard for Allostatic load measurement.

The project will also examine the association of allostatic load with age and social position within CLOSER.

Project description

Allostatic load is the concept of ‘wear and tear’ associated with the response to chronic or repeated stress. 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. 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, studies that have examined allostatic load are generally conducted in older age groups. It is unclear that the allostatic load construct remains stable by age or by other factors such as medication status. A number of studies have suggested that allostatic load varies by social position. Again a majority of these studies are conducted in older age groups and, while one suggests that social differences in allostatic load are only apparent in those aged under 75, further work is required to understand when in the lifespan the association of allostatic load with measures of social position emerges and disappears.

Plan of analyses

• Aim 1: To catalogue the biomarkers in the component studies within CLOSER and other studies such as Whitehall II, Twenty-07 and English Longitudinal Study of Ageing. 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.
• Aim 2: To scope the literature to examine which biological markers are typically included in the construction of allostatic load. We will examine which of the identified markers have been collected across the CLOSER studies with a focus on categorising them as primary or intermediate markers and to highlight how the inclusion/exclusion of different markers might affect our understanding of the construct. We will examine the impact of the addition of less typically assessed markers on the construction of allostatic load.

Additionally we propose two substantive research questions:

• Aim 3: To capitalise on the on-going work package that has harmonised measures of social position across the CLOSER studies and examine how social position is related to allostatic load and its construction.
• Aim 4: To capitalise on the wide age range available within CLOSER studies to examine how allostatic load evolves across the age span and the role of medication status in this evolution.

Project outputs

Cataloguing the components of allostatic load will assist researchers to understand the data from longitudinal studies, facilitate cross-cohort working and help to harmonise data across CLOSER and other cohort studies. In addition, the project will produce a guide on the biomarkers available across CLOSER studies, a guide to the construction of allostatic load and possible challenges in its use, as well as publications on social factors and their association with allostatic load, and the association of allostatic load with age.

Full list of data sources:

The CLOSER longitudinal studies are:
Hertfordshire Cohort Study (born 1930-39)
MRC National Survey of Health and Development (1946 British Cohort Study)
MRC National Survey of Health and Development (1946 British birth cohort study)
1958 National Child Development Study (1958 British birth cohort study)
1970 British Cohort Study
Avon Longitudinal Study of Parents and Children (Children of the 1990s)
Southampton Women’s Survey (women aged 20-34 enrolled in the study in 1998-2002)
Millenium Cohort Study (Child of the New Century, born 2000-2001)
Undertanding Society: The UK Household Longitudinal Study.
In addition, we plan to include other significant longitudinal studies such as The English Longitudinal Study of Ageing (ELSA), Whitehall II and the West of Scotland Twenty-07.