Background to pSoBid
Ill health has been long recognised as more prevalent in areas of relative social deprivation. Heart disease, diabetes, some cancers and rheumatoid arthritis are examples of the burden of ill-health that is carried disproportionately by people from poorer circumstances. Not only is the incidence of disease higher in these communities but also the nature of the problem (tumour type, severity of stroke, etc) appears to be qualitatively different (more aggressive with poorer prognosis). Whilst much of this variation can be laid at the door of classical risk factors such as smoking, physical activity, poorer diets and so on, these factors fail to account for the totality of the variation. Social gradients are present in a range of biological and psychosocial variables which indicate that living in a deprived environment may increase the propensity to develop chronic diseases, through as of yet unknown mechanisms.
This study is called pSoBid (pronounced 'so-bid') as it seeks to integrate established and new knowledge relating to the psychological, social, and biological determinants of health. This study has brought together expertise from social epidemiology, public health, biochemistry, psychology, neuroscience and genetics to examine the pathways between people's social circumstances, mental wellbeing, and biological markers of disease.
pSoBid seeks to identify a range of measures of these stress responses, and to examine to which they pattern according to stress in people's lives (including social circumstances as a proxy measure of chronic stress). In the longer term, such markers could be important intermediate indicators of the impact of social policy interventions on population health.
Growing evidence also indicates that risk factors measured in utero (in the womb), in the early childhood and even between generations, may be associated with the risk of cardiovascular disease and cancer in later life, pSoBid is also seeking to take account of early life experiences on adult health outcomes.
A central theme of this study is the concept of an individuals 'biological age' (as compared with 'chronological age'). People experiencing chronic stress will often have a biological age older than their chronological age. This may mean the individual looks older than their years and is sometimes described as having 'more miles on the clock'. Biological ageing is the progressive impairment of biological systems over time, creating a platform for disease development. Accelerated biological ageing in linked with earlier onset of diseases associated with ageing. Two novel measures of biological ageing are being used in pSoBid:
- Measurement of the intima-media thickness (IMT) of the carotid artery by high resolution ultrasound is now widely accepted non-invasive surrogate measure of atherosclerosis, and a reliable indicator of future risk of major coronary event. Since age is the strongest determinant of IMT, evaluation of carotid IMT as a marker of the degree of atherosclerosis and vascular ageing is one outcome measure used in pSoBid1, giving an index of the age of an individual's artery.
- Biological ageing is also being assessed at the molecular level, through measurement of telomere length. Telomeres are sequences of DNA at the end of chromosomes, and shorten slightly each time a cell divides.
A further feature that might either contribute to the poorer health associated with deprivation, or might act in a protective way, is mental state or outlook. pSoBid1 is using a range of tests of cognitive function and psychological state as a means of examining whether certain personality and other factors modify responses to stress and challenge, conferring either vulnerability or protection.
The study will also deploy neuro-imaging techniques with a small sub-sample of male participants, to add to understanding about brain changes associated with stress.
pSoBid commenced in January 2005 and the data collection was completed in May 2007.