B vitamin and/or ω-3 fatty acid supplementation and cancer: ancillary findings from the supplementation with folate, vitamins B6 and B12, and/or omega-3 fatty acids (SU.FOL.OM3) randomized trial.

Background: To advance knowledge about the cancer-chemopreventive potential of individual nutrients, we investigated the effects of B vitamin and/or ω-3 fatty acid supplements on cancer outcomes among survivors of cardiovascular disease.

Methods: This was an ancillary study of the Supplementation With Folate, Vitamins B(6) and B(12) and/or Omega-3 Fatty Acids (SU.FOL.OM3) secondary prevention trial (2003-2009). In all, 2501 individuals aged 45 to 80 years were randomized in a 2 × 2 factorial design to one of the following 4 daily supplementation groups: (1) 5-methyltetrahydrofolate (0.56 mg), pyridoxine hydrochloride (vitamin B(6); 3 mg) and cyanocobalamin (vitamin B(12); 0.02 mg); (2) eicosapentaenoic and docosahexaenoic acid (600 mg) in a 2:1 ratio; (3) B vitamins and ω-3 fatty acids; or (4) placebo. Overall and sex-specific hazard ratios (HRs) and 95% CIs regarding the cancer outcomes were estimated with Cox proportional hazards models.

Results: After 5 years of supplementation, incident cancer was validated in 7.0% of the sample (145 events in men and 29 in women), and death from cancer occurred in 2.3% of the sample. There was no association between cancer outcomes and supplementation with B vitamins (HR, 1.15 [95% CI, 0.85-1.55]) and/or ω-3 fatty acids (HR, 1.17 [95% CI, 0.87-1.58]). There was a statistically significant interaction of treatment by sex, with no effect of treatment on cancer risk among men and increased cancer risk among women for ω-3 fatty acid supplementation (HR, 3.02 [95% CI, 1.33-6.89]).

Conclusion: We found no beneficial effects of supplementation with relatively low doses of B vitamins and/or ω-3 fatty acids on cancer outcomes in individuals with prior cardiovascular disease. Trial Registration  isrctn.org Identifier: ISRCTN41926726.