Health inequalities are known to be prevalent in Britain. Though testing hypothesised pathways between socio-economic position and biological markers of heath, this thesis aims to improve understanding of how socio-economic inequality becomes health inequality and how physiology is affected by socio-economic position. Using Understanding Society data, access is gained to a range of biomarkers collected cross-sectionally from an adult age range. Methods such as regressions, decompositions and mixed-models are used to identify mediators of SEP’s association with grip strength, self-reported type two diabetes, glycated haemoglobin and lung function. The mediators explored are material deprivation and exposures, psychosocial stress and health behaviours. Using retrospective socio-economic position measures, consideration is paid to the timing of disadvantage, while the wide age range enables identification of when inequalities emerge. Disadvantaged socio-economic position in childhood and adulthood were negatively associated with grip strength, though the gradient does not emerge until mid-adulthood. Health behaviours only slightly mediated this association and childhood socio-economic position continued to be important in adulthood. Support was found for mediation of socio-economic position’s association with self-reported type two diabetes, but not with glycated haemoglobin. The mediation was mainly via obesity with no significant mediation through material deprivation, psychosocial stress or health behaviours. Inequalities in lung function were observable at all adult ages and appeared to worsen with increasing age. Material exposures and health behaviours mediated this. Childhood socio-economic position was important in adulthood and moderated the effect of some exposures and health behaviours. This thesis finds that early disadvantage can have lasting effects. The lack of support for mediation in some outcomes suggests the need to address social inequalities directly, while the identification of mediating mechanisms in other outcomes indicates ways to alleviate these processes.