The impact of metabolic syndrome on major adverse cardiovascular events (MACE) in young adults with acute coronary syndrome: a GRADED systematic review and meta-analysis

While Metabolic Syndrome (MetS) is a recognized driver of cardiovascular disease, its specific prognostic impact on Major Adverse Cardiovascular Events (MACE) in young adults presenting with Acute Coronary Syndrome (ACS) remains poorly defined. This systematic review and meta-analysis aimed to evaluate the association and clinical consequences of MetS on primary outcomes, including MACE, in this increasingly affected demographic. Registered in PROSPERO (CRD420261423823) , a systematic search of PubMed, Google Scholar, and CENTRAL (initiation to June 2026) identified observational studies on young adults (younger than 45 or 50 years) with ACS and MetS defined by validated criteria. Data on baseline characteristics and primary outcomes—including MACE, recurrent myocardial infarction (re-MI), and stroke—were extracted. Pooled Risk Ratios (RR) were estimated using a random-effects model. Four high-quality studies encompassing 3,691,728 participants were included. MetS was associated with an approximate two-fold increase in MACE risk (RR: 1.93; 95% CI: 1.83–2.03). Elevated risks were also observed for re-MI (RR: 2.08; 95% CI: 1.17–3.68) and stroke (RR: 2.33; 95% CI: 1.38–3.91). Subgroup analysis successfully explained initial heterogeneity in stroke ( I 2 = 0% in medium-term follow-up) and re-MI through follow-up duration and diagnostic criteria. The overall certainty of evidence was graded as Moderate for all primary outcomes under the GRADE framework. MetS is a significant independent predictor of adverse cardiovascular outcomes in young ACS survivors. These findings underscore the necessity for early risk stratification and aggressive metabolic management to mitigate the nearly two-fold increase in clinical risk.