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Objectives: We examined how asymptomatic metabolic syndrome (MetS) in midlife affects cardiovascular (CV) morbidity and all-cause mortality later in life and studied difference in time to event and from the individual components related to MetS.

Design: Population-based matched cohort study including data from a screening programme for identification of CV risk factors.

Setting: Primary care, County of Vastmanland, Sweden.

Participants: All inhabitants turning 40 or 50 years between 1990 and 1999 were invited to a health screening. Total 34 269 (60.1%) individuals completed the health examination. Participants that met a modified definition of MetS were individually matched to two controls without MetS with regard to age, sex and date of health examination.

Interventions: None.

Main outcome measures: CV events and all-cause mortality from the index examination to June 2022.

Results: All 5084 participants with MetS were matched to two controls. There were 1645 (32.4%) CV events in the MetS group and 2321 (22.8%) CV events for controls. 1317 (25.9%) MetS and 1904 (18.7%) control subjects died. The adjusted HRs (aHR) for CV event and death were significantly higher when MetS was present (aHR) 1.39*** (95% CI 1.28 to 1.50) and 1.27*** (95% CI 1.16 to 1.40) respectively. The factor analysis identified three dominating factors: blood pressure, cholesterol and blood glucose. Mean time for first CV event and death was 2.6 years and 1.5 years shorter respectively for participants within the highest quartile compared with participants with lower mean arterial blood pressure (MAP). The aHR for each 10 mm Hg increased MAP were 1.19*** (95% CI 1.15 to 1.23) for CV event and 1.16*** (95% CI 1.11 to 1.21) for death.

Conclusion: The risk of a CV event and premature death is significantly increased when MetS is present. Early detection of metabolic risk factors, especially, high blood pressure, opens a window of opportunity to introduce preventive treatment to reduce CV morbidity and all-cause mortality.