Researchers at the University of California say that participants who took about 500 milligrams of vitamin C supplements per day saw a 24 per cent drop in plasma C-reactive protein (CRP) levels after two months. Recent research suggests that CRP may be a better predictor of heart disease than cholesterol levels.
"C-reactive protein is a marker of inflammation, and there is a growing body of evidence that chronic inflammation is linked to an increased risk of heart disease, diabetes and even Alzheimer's disease," said Gladys Block, UC Berkeley professor of epidemiology and public health nutrition and lead author of the study.
If our finding of vitamin C's ability to lower CRP is confirmed through other trials, vitamin C could become an important public health intervention, she added.
The study, published in the April issue of the Journal of the American College of Nutrition (vol 23, no 2, 141-147), is the first to show that vitamin C can decrease levels of CRP, a biomarker that has garnered increasing attention among health researchers in recent years.
Inflammation occurs as part of the body's defence against infection or injury. The body triggers the production of inflammatory cytokines, such as interleukin-6, that then triggers the production of CRP by the liver.
"CRP levels can go up 100-fold within a short period of time as a reaction to an infection, but they then drop back down rapidly after the acute infection passes," said Christopher Jensen, a research scientist in Block's lab and co-author of the paper.
"It's not clear how vitamin C was able to lower CRP levels for people in this study," he added.
The scientists theorise that vitamin C may suppress the production of cytokines, but they assert that this hypothesis needs to be investigated through future studies.
They say that long-term adverse health effects occur when inflammation persists at low levels. This chronic inflammation, with persistent low levels of CRP, has been found among smokers and type 2 diabetics, as well as among overweight or obese persons. Scientists have only recently begun to understand such chronic inflammation as an important factor in disease.
"Several large studies have suggested that CRP may be a better predictor of heart disease than cholesterol levels, although this has been questioned," said Marion Dietrich, a UC Berkeley researcher in nutritional epidemiology and another co-author of the study.
"CRP is widely recognised as an important biomarker for inflammation. Elevated CRP concentrations have been found in obese people, indicating that obesity is associated with chronic inflammation. The association may help explain why overweight people are at increased risk for chronic disease development such as diabetes, heart disease or certain types of cancer."
For the study, researchers tested 160 healthy adults from Berkeley and Oakland in California who either smoked or were exposed to second-hand smoke. The researchers adjusted for body mass index and baseline CRP concentrations. People who had high levels of CRP to start with, likely due to existing illness, were excluded from the study.
Participants were randomly assigned to receive a daily dose of a placebo, a vitamin C supplement of about 500 milligrams, or a mixture of antioxidants made up of vitamin C, vitamin E and alpha-lipoic acid. Neither the researchers nor the participants knew which group a subject belonged to in the double-blind study.
Plasma CRP levels were measured from blood samples before and after the two-month trial. Levels of CRP decreased significantly, by 24 per cent, among participants who had taken the vitamin C pills when compared to those in the placebo group. For those taking the antioxidant mixture, levels of CRP decreased 4.7 percent compared to the placebo group, but the change was not statistically significant.
The researchers noted that in other studies, higher doses of vitamin E produced lower CRP levels among type 2 diabetics and healthy individuals.
"We were surprised to find no statistical change in CRP levels among people taking the antioxidant mixture, while those taking the vitamin C supplement saw a significant 24 per cent drop," said Block. "However, the only other study to administer vitamin C and vitamin E together also did not show an effect on CRP."
It is possible that there is some interaction among the antioxidants that rendered the mixture less effective in reducing CRP levels, but that is not clear at this time, said Block.
Block has been awarded a grant to conduct another randomised trial of vitamin C and CRP levels in order to confirm the findings.