Vitamin C intake and breast cancer mortality in a cohort of Swedish women

Prospective cohort of 3405 women with invasive breast cancer from the Swedish Mammography Cohort; diagnosed 1987-2010; dietary data collected via FFQ at baseline (1987) and in 1997; post-diagnosis supplement data available for a subset; hazard ratios estimated by Cox models for death from any cause and breast cancer-specific mortality.

Post-diagnosis vitamin C supplement use; dosage and duration not reported; 14.1% of 717 post-diagnosis cases reported using a vitamin C-containing supplement in 1997.

Pre-diagnosis dietary vitamin C intake was associated with lower breast cancer-specific mortality: highest vs lowest quartile HR 0.74 (0.57-0.98); adjusted HR 0.75 (0.57-0.99); P trend 0.04 (unadjusted) and 0.03 (adjusted). Total mortality showed a borderline association (HR 0.84; 0.71-1.00; P trend 0.08). Post-diagnosis vitamin C supplement use showed no association with breast cancer-specific mortality (HR 1.06; 0.52-2.17). Stronger inverse associations were observed for ER-negative/PR-negative tumors (HR 0.46; 0.22-0.96) and among age ≥65 (HR ~0.48). Never-smokers showed a stronger inverse association (HR 0.53; 0.28-0.99). Regular multivitamin use was not associated with mortality. Conclusion: Dietary vitamin C intake before diagnosis may be linked to better breast cancer survival; post-diagnosis supplementation showed no survival benefit; results are observational; further research is needed.

Observational design; dietary assessment via FFQ; post-diagnosis supplement analysis limited to 717 cases with 66 breast cancer deaths (limited power); 79% had only pre-diagnosis diet data; potential residual confounding; generalizability limited to Swedish women.