Purpose: Micronutrients may protect against prostate cancer. However, few studies have had high-quality assessment of both dietary and supplemental consumption of micronutrients, rendering possible different source-specific effects difficult to discern. This study evaluates associations between intake of vitamin C, E, folate, and beta-carotene and prostate cancer risk, focusing on possible different effects of dietary, supplemental, or total intake and on potential effect modification by alcohol intake and BMI. Methods: Danish prospective cohort study of 26,856 men aged 50-64 years with questionnaire-based information on diet, supplements, and lifestyle. Hazard ratios (HRs) for prostate cancer associated with micronutrient intake were calculated using Cox proportional hazard analyses. Results: During follow-up (1993-2010), 1,571 prostate cancer cases were identified. Supplemental folic acid was inversely associated with prostate cancer risk, notably on a continuous scale [HR 0.88 (95 % CI 0.79-0.98) per 100 µg increase/day]. The risk reduction was largely confined to non-aggressive tumors [HR 0.71 (0.55-0.93) per 100 µg increase/day]. No influence on prostate cancer risk was observed for dietary folate or for the other studied micronutrients, regardless of source. We found no significant effect modification by alcohol intake and BMI in relation to any micronutrient. Conclusion: Our study may indicate an inverse association between folic acid and prostate cancer; however, the inverse association was confined to supplemental folic acid and non-aggressive prostate cancer and may thus be a chance finding. Further studies are warranted to evaluate our findings.