This prospective study investigates the association between plasma 25-hydroxyvitamin D (25(OH)D) concentrations and the risk of myocardial infarction (MI) in a cohort of 18,225 male health professionals aged 40 to 75 years. During a 10-year follow-up period, 454 men developed MI or fatal coronary heart disease (CHD). The study used a nested case-control design with a 2:1 ratio of cases to controls, matched for age, date of blood draw, and smoking status. Key findings include: - Men with 25(OH)D levels ≤5 ng/mL had an increased risk of MI compared to those with sufficient levels (≥30 ng/mL) (relative risk [RR]=2.42; 95% confidence interval [CI], 1.53–3.84; *P* for trend <0.001). - After additional adjustments for various risk factors, the relationship remained significant (RR=2.09; 95% CI, 1.24–3.54; *P* for trend=0.02). - Even men with intermediate 25(OH)D levels (22.6–29.9 ng/mL) had an elevated risk compared to those with sufficient levels (RR=1.60; 95% CI, 1.10–2.32; *P* for trend=0.001). The study concludes that optimal levels of 25(OH)D should be at least 30 ng/mL to lower the risk of MI. The findings support the hypothesis that vitamin D deficiency is an independent risk factor for MI, independent of other cardiovascular disease (CVD) risk factors.This prospective study investigates the association between plasma 25-hydroxyvitamin D (25(OH)D) concentrations and the risk of myocardial infarction (MI) in a cohort of 18,225 male health professionals aged 40 to 75 years. During a 10-year follow-up period, 454 men developed MI or fatal coronary heart disease (CHD). The study used a nested case-control design with a 2:1 ratio of cases to controls, matched for age, date of blood draw, and smoking status. Key findings include: - Men with 25(OH)D levels ≤5 ng/mL had an increased risk of MI compared to those with sufficient levels (≥30 ng/mL) (relative risk [RR]=2.42; 95% confidence interval [CI], 1.53–3.84; *P* for trend <0.001). - After additional adjustments for various risk factors, the relationship remained significant (RR=2.09; 95% CI, 1.24–3.54; *P* for trend=0.02). - Even men with intermediate 25(OH)D levels (22.6–29.9 ng/mL) had an elevated risk compared to those with sufficient levels (RR=1.60; 95% CI, 1.10–2.32; *P* for trend=0.001). The study concludes that optimal levels of 25(OH)D should be at least 30 ng/mL to lower the risk of MI. The findings support the hypothesis that vitamin D deficiency is an independent risk factor for MI, independent of other cardiovascular disease (CVD) risk factors.