NEW YORK (AP) — Vitamin C’s theorized ability to protect against cancer and heart disease appears to diminish at high doses, possibly becoming harmful, a researcher says.
A study indicates that at 500 milligrams a day, “it’s really no particular help at all” in discouraging oxidation, a damaging chemical reaction linked in theory to cancer and heart disease, said Joseph Lunec of Leicester University in England.
The study found evidence that at 500 milligrams, Vitamin C both suppresses and promotes oxidation, with the effects apparently canceling themselves out, Lunec said.
At even higher doses, Lunec suggested, the harmful effects might prevail. That is, Vitamin C might actually promote oxidation.
Experts were wary of Lunec’s brief report, which appears in the April 9 issue of the journal Nature.
The dose tested in the study is a bit more than eight times the standard recommended dietary allowance, but it can be found in some supplements sold at stores.
At 500 milligrams a day, “although we see a profound protective effect, we also see a definite adverse effect” that “would negate any protective effect you have,” Lunec said Wednesday.
He and his colleagues gave 30 healthy volunteers 500 milligrams of vitamin C a day for six weeks. Before and during the vitamin treatment, researchers looked at two indicators of oxidation damage in DNA from the volunteers’ white blood cells. While the volunteers were taking supplements, one indicator showed less oxidation and the other indicator showed more, compared to before the supplementation began.
That raises questions about the vitamin’s antioxidant abilities at this dose, the researchers said.
But Dr. Steven Zeisel of the University of North Carolina at Chapel Hill said the mixed result is puzzling. The study “is not a definitive help in our understanding about whether vitamin C is protective or not” at high doses, he said.
Bruce N. Ames of the University of California at Berkeley said he suspects the result may have been influenced by the study’s lab procedures. Dr. Mark Levine of the National Institutes of Health said the volunteers’ white cells may have been saturated with vitamin C before they took supplements. If so, it’s hard to see how supplements could make any difference, he said.
Lunec said that researchers are now studying why the mixed result occurred, but that it is not surprising.