Vitamin C shown to lower levels of inflammation biomarker
| 20 November 2008
BERKELEY — A new study led by Berkeley researchers adds to the evidence that vitamin-C supplements can lower concentrations of C-reactive protein (CRP), a central biomarker of inflammation that has been shown to be a powerful predictor of heart disease and diabetes. The same study found no benefit from daily doses of vitamin E, another antioxidant.
This study comes just days after a larger, eight-year clinical trial led by researchers at Boston's Brigham and Women's Hospital failed to show that vitamins C or E could cut the risk of heart attacks or strokes.
That trial does not necessarily close the book on the benefits of vitamin C for cardiovascular health, according to Gladys Block, professor emeritus of epidemiology and public health nutrition and lead author of the Berkeley study. She pointed out that the Brigham and Women's Hospital study did not screen study participants for elevations in CRP — defined by the American Heart Association as 1 milligram per liter or greater — which is an important distinction in determining who might benefit from taking vitamin C.
The study led by Block shows that for healthy, non-smoking adults with an elevated level of CRP, a daily dose of vitamin C lowered levels of the inflammation biomarker after two months compared with those who took a placebo. However, participants who did not start out with elevated CRP levels saw no benefit from vitamin C supplementation.
"This is an important distinction; treatment with vitamin C is ineffective in persons whose levels of CRP are less than 1 milligram per liter, but very effective for those with higher levels," said Block. "Grouping people with elevated CRP levels with those who have lower levels can mask the effects of vitamin C. Common sense suggests, and our study confirms, that biomarkers are only likely to be reduced if they are not already low."
The researchers said that for people with elevated CRP levels, the amount of CRP reduction achieved by taking vitamin C supplements in this study is comparable to that in many other studies of cholesterol-lowering drugs called statins. They noted that several larger statin trials lowered CRP levels by about 0.2 milligrams per liter; in this latest study, vitamin C lowered CRP by 0.25 milligrams per liter.
"This finding of an effect of vitamin C is important because it shows in a carefully conducted randomized, controlled trial that for people with moderately elevated levels of inflammation, vitamin C may be able to reduce CRP as much as statins have done in other studies," said Block.
The Berkeley study also found a strong link between obesity and elevated levels of CRP. While 25 percent of normal-weight people had elevated levels of CRP, those levels were found in 50 percent of overweight and 75 percent of obese participants.
Evidence of the link between elevated CRP levels and a greater risk of heart disease has grown in recent years. The American Heart Association and the U.S. Centers for Disease Control and Prevention recommends that clinicians measure CRP levels in patients who have a moderately elevated risk of cardiovascular problems, as determined by other established risk factors such as high cholesterol levels and smoking.
"Major studies have found that the level of CRP in the body predicts future risk of cardiovascular disease, including myocardial infarction, stroke, and peripheral artery disease, as well as diabetes," said Block. "Some believe CRP to be as important a predictor of future heart problems as high levels of LDL and low levels of HDL cholesterol."