The researchers have also found in the same study that daily doses of vitamin E, another antioxidant, are not very beneficial.
The findings emerge just days after an eight-year clinical trial, led by researchers at Boston's Brigham and Women's Hospital, failed to confirm that vitamins C or E supplements could prevent heart attacks or strokes.
Gladys Block, UC Berkeley professor emeritus of epidemiology and public health nutrition, said that their study did not close the books on the benefits of vitamin C for cardiovascular health.
She said 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.
She insisted that her study showed 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, the study published in the journal Free Radical Biology and Medicine did not find any benefit from vitamin C supplementation for participants that did not start out with elevated CRP levels.
"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. 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," said Block.
She reckoned that for people with elevated CRP levels, the amount of CRP reduction achieved by taking vitamin C supplements in the study was comparable to that in many other studies of cholesterol-lowering drugs called statins.
While several larger statin trials lowered CRP levels by about 0.2 milligrams per liter, she said, the present study showed that vitamin C lowered these levels 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 researchers, however, are uncertain as to why vitamin E did not show an effect even though it is also an antioxidant.
Block thinks that the difference perhaps relates to the fact that vitamin E is fat soluble and thus found in cell membranes, while vitamin C is water soluble and found in intercellular fluid.
Though the study lasted for two months only, the researchers insist that there is no evidence to date of adverse effects for longer-term use of vitamin C at high levels.
They agree that further studies are required to see whether vitamin C's beneficial impact on CRP levels continue past two months.
"This is clearly a line of research worth pursuing. It has recently been suggested by some researchers that people with elevated CRP should be put on statins as a preventive measure. For people who have elevated CRP but not elevated LDL cholesterol, our data suggest that vitamin C should be investigated as an alternative to statins, or as something to be used to delay the time when statin use becomes necessary," said Block.