Risk factor exposure in individuals free from cardiovascular disease differs according to age at first myocardial infarction

BACKGROUND: The pathophysiology of myocardial infarction (MI) may differ depending on whether it occurs early or late in life. We tested the hypothesis that risk factor pattern differs according to the age at MI. METHODS: We performed a matched case-control study in the population-based Malmö Preventive Project (n = 33 346), where 3687 individuals developed MI during 22 ± 7 years of follow-up (=cases). The cases were divided into quartiles (Q1-Q4) according to age at event and were assigned two matched controls free from MI during follow-up. We used conditional logistic regression to assess relationship between risk factors at baseline and case status within quartiles of age at incident MI. RESULTS: The median (range) age (years) at incident MI in Q1 was 52.9 (37.0-57.1), Q2 60.8 (57.1-63.6), Q3 66.6 (63.6-69.7), and Q4 73.5 (69.7-84.0). The odds ratio (95% CI) for incident MI associated with 1 SD increase of baseline cholesterol decreased with age of MI and was 1.68 (1.50-1.87) for Q1, 1.43 (1.28-1.61) for Q2, 1.27 (1.14-1.42) for Q3, and 1.08 (0.98-1.19) for Q4. Similarly, family history of MI had a stronger relationship with MI in Q1 than with MI in Q4 of MI age, whereas smoking displayed a U-shaped relationship. Exposure to the remaining risk factors did not differentially affect MI occurring at different age spans. CONCLUSION: Exposure to cholesterol and family history of MI more strongly predicts onset of MI at younger ages, suggesting that MI in younger subjects is preceded by a different risk factor pattern than MI presenting in older subjects.