Social environments and lifestyles linked to mortality and future health risks in metabolic syndrome: evidence from UK and US nationwide cohort studies.

INTRODUCTION

Metabolic syndrome (MetS) poses a major public health challenge. This study examined how social environments and their interactions with lifestyle behaviours influence mortality, life expectancy and disease risks in adults with MetS from the UK and USA.

METHODS

Adults with MetS were identified from the UK Biobank (2006-2010, n=60 423; mean follow-up 12.8 years) and US National Health and Nutrition Examination Survey (NHANES) (1999-2018, n=11 170; mean follow-up 8.0 years). Weighted scores for social environment (socioeconomic status, social capital, healthcare access, built environment) and healthy lifestyle (smoking, alcohol, physical activity, diet) were categorised into tertiles. Primary outcomes were all-cause and cause-specific mortality (cardiovascular disease (CVD), cerebrovascular disease (CBVD), chronic kidney disease (CKD)) in both cohorts and incident diseases in UK Biobank. Cox regression assessed associations and interactions.

RESULTS

Unfavourable (vs favourable) social environments were associated with higher all-cause mortality in UK Biobank (HR 1.72, 95% CI 1.62 to 1.83) and NHANES (HR 2.30, 95% CI 1.95 to 2.71), with consistent patterns for CVD, CBVD and CKD outcomes. Life expectancy at age 45 was reduced by 3.49 (95% CI 3.40 to 3.57) years (UK Biobank) and 7.81 (95% CI 7.56 to 8.07) years (NHANES). Social environments contributed substantially to mortality burden (population attributable fraction: 17.0% and 24.1%, respectively), largely driven by socioeconomic status and social capital. Significant interactions showed that healthy lifestyles conferred stronger protection in unfavourable environments. Joint exposure to unfavourable environment and unhealthy lifestyle markedly increased mortality risk (HRs 2.5-3.5).

CONCLUSIONS

Unfavourable social environments consistently predict adverse outcomes in MetS across contexts. Their synergy with lifestyle behaviours underscores the need for integrated interventions addressing both environmental and behavioural factors, especially in disadvantaged populations.