If you have a bruise, a muscle sprain, an inflammatory disease or if you take iron supplements, exceeding 100 mg per day of vitamin C may be damaging to your body, according to a study by University of Florida researchers.
Body May Rust Inside If Vitamin C Over Maximum Dose
That's because all of those conditions produce free iron, which reacts negatively with vitamin C in much the same way that the iron on bicycles and fences reacts with water and oxygen.
"You will rust inside, so to speak," said Christiaan Leeuwenburgh, the senior author and an assistant professor in UF's department of exercise and sport sciences.
In a study published this month in the journal Free Radical Biology and Medicine, several UF researchers worked with renowned vitamin C expert Barry Halliwell to test the effects of vitamin C and N-acetyl-cysteine (NAC, another water-soluble antioxidant) at the cellular level.
In this study, the researchers began with the hypothesis that vitamin C and NAC would speed the recovery of a muscle injury because of their anti-oxidant properties and ability to reach damaged cells quickly.
Fourteen healthy men volunteered to have one of their arms injured by a machine that ruptured their bicep muscles and created swelling. Researchers then gave half of them a placebo and the other half a drink supplemented with about 700 mg of vitamin C and 800 mg of NAC.
"Initially, the vitamin C and NAC were given to prevent the injury, because we thought they'd have protective effects," Leeuwenburgh said. "Instead, they were damaging."
Leeuwenburgh attributes the damaging effects of the vitamin C and NAC to their reaction with iron in the body. Normally, iron is bound to proteins and enzymes and therefore can't react with vitamin C and NAC.
But when inflammation occurs -- as it does in muscular injuries and a variety of diseases such as Alzheimer's, arthritis and cardiovascular disease -- the body releases more free iron, which is highly reactive to outside elements -- in this case, vitamin C and NAC. Indeed, the researchers showed that there were increases in free iron following this type of exercise.
"Vitamin C isn't bad, and neither is NAC, but by some mechanism in this situation there were some pro-oxidant effects of supplementation," said April Childs, a graduate student in the department of exercise and sport sciences and the lead author of the study.
And although Leeuwenburgh says people who have taken vitamin C or NAC in the past shouldn't worry too much about the new finding, he recommends caution in supplementing vitamin C in doses greater than 100 mg after injuries or disease condition characterized by increases in free iron.
"People should limit their vitamin C intake until we know more," he said. "Everyone agrees that after 80 to 90 milligrams, about the recommended daily allowance, it goes out of your body since measurements show that white blood cells are saturated completely after this dose. You'd think that if it goes out of your body it isn't harmful, but maybe the high transient levels do react in a negative way. There's no benefit to taking more than the RDA, and it could actually harm you."
Furthermore, he said, "Vitamin C is believed to prevent cancer, but instead, it may be damaging. Studies performed in humans actually show that it may increase DNA damage."
Because vitamin C and NAC in the body appear to react most negatively with iron, Leeuwenburgh said, those with inflammatory diseases and those who take more than the recommended daily allowance of iron should be particularly vigilant about limiting their vitamin C and NAC intake.
"If you're taking more than the RDA of iron, you're putting yourself at risk by taking more than the RDA of vitamin C or NAC at the same time," Leeuwenburgh said. "Iron is very important in preventing anemia. So many people -- particularly women -- are supplementing, and the effects of supplementing iron and vitamin C for long periods have not been adequately studied.
"Therefore, to supplement vitamin C and iron together may be damaging. Further studies are required to fully understand the antioxidant and pro-oxidant nature of vitamin C," Leeuwenburgh concluded.
[Contact: Christiaan Leeuwenburgh, Kristin Harmel]