Socioeconomic inequalities in allostatic load in a large Norwegian cohort study: the NCDNOR project

BACKGROUND: Allostatic load (AL) is the physiological burden of stress, and it is suggested to be a mediator between socioeconomic position and health. The aim of this article was to study life-course trajectories in levels of AL by employing data collected over three decades (1994-2019) to compare sex and socioeconomic groups in the adult Norwegian population. METHODS: Harmonised data from the following Norwegian health studies were used: the Trøndelag Health Study, the Tromsø Study, the Age 40 Program and CONOR. In total, 264 824 participants aged 30-79 years contributed with 346 312 health examinations. A combined AL score was calculated as the number of biomarkers in the worst quartile among the following eight variables: systolic blood pressure, diastolic blood pressure, resting heart rate, triglycerides, total cholesterol, high-density lipoprotein cholesterol, body mass index and waist-hip ratio. High-sensitivity C reactive protein and glycated haemoglobin were included in sensitivity analyses for a subset of participants. Life-course trajectories were analysed by using a linear mixed model. A shared-parameter model was employed to evaluate attrition caused by death. RESULTS: Participants with primary education had higher AL compared with secondary and tertiary educated people in all age groups. Men had higher AL than women throughout the life-course. Overall, AL increased with age but levelled off at higher ages among women and decreased at higher ages among men. CONCLUSIONS: We found significant socioeconomic inequalities and sex differences in AL throughout the life-course. This highlights a potential for improvement in public health by effective treatment and public health measures to reduce AL inequities.