Distribution of LDL-Cholesterol Levels and Their Associations With Cardiovascular Outcomes in Young Adults Under 40 Years in South Korea: A Nationwide Cohort Study

Objective: We examined the distribution of low-density lipoprotein cholesterol (LDL-C) levels and compared the hazards of myocardial infarction (MI), stroke, and their composite according to LDL-C concentration in young adults.Methods: This was a nationwide, population-based study.From the Korean National Health Insurance Service database (2002-2022), we identified adults aged 20-39 years without prior MI or stroke who underwent at least 1 health examination between 2009 and 2012 (n=6,458,006).The hazards of MI, stroke, and their composite were evaluated across LDL-C levels.Results: During a median follow-up of 12.6 years, 47,107 MIs, 28,536 strokes, and 73,897 composite events occurred.The hazard of outcomes showed a J-shaped association with LDL-C levels, with the lowest hazard observed around 90-110 mg/dL.Above this range, the hazard increased progressively with rising LDL-C levels.In analyses based on LDL-C categories, levels 130 mg/dL were associated with significantly increased hazards of outcomes, with the highest hazards observed at 160 mg/dL.The elevated hazards in the higher LDL-C categories were more pronounced in individuals with abdominal obesity and current smokers for all 3 outcomes, and in those with higher body mass index categories, low high-density lipoproteincholesterol, and hypertriglyceridemia for MI and the composite outcome.Conclusion: Among young adults, cardiovascular risk demonstrated a J-shaped association with LDL-C levels.Risks increased progressively beyond approximately 90-110 mg/dL, especially in the presence of other cardiometabolic risk factors.These findings underscore the importance of lipid monitoring and cardiovascular risk assessment even in young adults, particularly those with concurrent risk factors.