Antioxidant vitamins protect healthy cells, but some doctors fear they may also protect cancer cells, reducing the effects of radiation and chemotherapy treatment.
In one study, researchers interviewed 4,877 women being treated for invasive breast cancer, aged 20 to 75, and followed up for four years. Compared to women who did not take supplements, those who took normal doses of vitamins E or C, or multi-vitamins were 15 percent more likely to survive and 18 percent less likely to see cancer recur. Survival rates rose and recurrence rates fell the longer the women took supplements. Researchers concluded antioxidants did not interfere with treatment.