Both dietary supplements contain 105 micrograms of the trace mineral selenium per daily dose, or about twice the Recommended Daily Allowance, which is 55 micrograms a day for adults, according to the center.

CNN: Group threatens suit over vitamins' anti-cancer claims

Each year brings a drumbeat of lab studies suggesting links between various dietary chemicals and cancer prevention: broccoli, soy, ketchup, bran, selenium.

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