RATIONALE In young adults, the role of mildly abnormal lipid levels and lipid variability in the risk of atherosclerotic cardiovascular diseases remains uncertain.

OBJECTIVE To investigate the association of these abnormalities in lipid profiles with the risk of myocardial infarction (MI) and stroke in young population.

METHODS AND RESULTS From the Korean National Health Insurance Service, a nationwide population-based cohort of 1 934 324 statin-naive adults aged 20 to 39 years, with ≥3 lipid profile measurements and without a history of MI and stroke, were followed-up until the date of MI or stroke, or December 31, 2017. The primary measure of lipid variability was variability independent of the mean. Higher baseline total cholesterol, LDL-C (low-density lipoprotein-cholesterol), and triglycerides and lower HDL-C (high-density lipoprotein-cholesterol) levels were significantly associated with increased MI risk; respective adjusted hazard ratios and 95% CIs comparing the highest versus lowest quartiles were 1.35 (1.20-1.53) for total cholesterol, 1.41 (1.25-1.60) for LDL-C, 1.28 (1.11-1.47) for triglycerides, and 0.82 (0.72-0.94) for HDL-C. Adjusted analyses for deciles of lipid profiles showed that MI risk was significantly elevated among participants with total cholesterol ≥223.4 mg/dL, LDL-C ≥139.5 mg/dL, HDL-C ≤41.8 mg/dL, and triglycerides ≥200.1 mg/dL. The associations between lipid levels and stroke risk were less prominent. Multivariable-adjusted restricted cubic spline analysis demonstrated that the increase in MI risk was not exclusively driven by extreme values of lipid profiles. Similar results were obtained on sensitivity analyses of baseline lipid levels. However, associations between lipid variability and the risk of MI and stroke varied depending on the measure of lipid variability used.

CONCLUSIONS Mildly abnormal baseline lipid levels were associated with an increased future risk of atherosclerotic cardiovascular disease events, particularly MI, whereas measures of lipid variability were not. Therefore, in young adults, achieving optimal lipid levels could be valuable in the prevention of atherosclerotic cardiovascular disease.