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Higher vitamin C levels, intake linked with lower risk of stroke

Tuesday, December 10, 2013. The results of a meta-analysis described online on November 27, 2013 in the Journal of the American Heart Association reveal a protective effect for having a high vitamin C level or consuming more of the vitamin against the risk of stroke.

Researchers selected twelve prospective studies involving vitamin C intake and six that examined serum or plasma vitamin C levels for their analysis. Studies of dietary vitamin C included a total of 217,454 men and women, in whom 3,762 strokes occurred over durations of 6.1 to 30 years. Among the 29,648 participants in the studies involving circulating vitamin C, there were 989 cases of stroke over follow-up periods ranging from 9.5 to 20 years.

For studies that examined vitamin C intake, subjects whose intake was classified as high had a 19% lower risk of stroke in comparison with those categorized as low. For each 100 milligram per day increase, the researchers uncovered a 17% lower risk of stroke. Analysis of studies that reported supplemental vitamin C intake also indicated a protective effect; however, there were only three studies that provided this data.

Pooled analysis of participants in studies of plasma or serum vitamin C revealed a 38% lower risk of stroke for subjects with high versus low levels. Each 20 micromole per liter increase in circulating vitamin C was found to be associated with a 19% lower risk of stroke.

"Vitamin C is a strong antioxidant, and has been shown to reduce the oxidation of low-density lipoproteins, to inhibit the proliferation of smooth muscle, to protect membrane from peroxidation, and ultimately to slow the progression of atherosclerosis," the authors write. "There is also growing evidence that systemic inflammation is involved in stroke etiology and pathology, and plasma or dietary vitamin C has been suggested to have antiinflammatory properties. Vitamin C intake in plasma has also been demonstrated to be inversely associated with blood pressure."

They suggest greater vitamin C consumption for populations with low intake or who are at high risk of stroke and suggest that, since established risk factors appear to be responsible for only half of the cases of stroke that occur, vitamin C levels could serve as an additional predictor of risk.