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

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.

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Higher vitamin C levels associated with lower risk of stomach cancer

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The November 2013 issue of the American Journal of Clinical Nutrition reports a protective effect for higher plasma vitamin C levels against gastric adenocarcinoma in Chinese men and women.

The current study involved follow-up participants in the Linxian General Population Nutrition Intervention Trial, which concluded in 1991. Blood samples collected between 1999 and 2000 were analyzed for plasma vitamin C levels. Four hundred sixty-seven men and women diagnosed with gastric adenocarcinoma and 618 subjects with esophageal squamous cell carcinoma were compared with 948 subjects who did not have the diseases.

A lower risk of gastric cancer was observed in association with higher plasma vitamin C levels. Participants with normal vitamin C levels, defined as greater than 28 micromoles per liter, had a 27% lower risk of gastric cancer in comparison with those whose levels were low at 28 micromoles per liter or less. A meta-analysis that included the current study and two other cohort studies resulted in similar findings. No association for vitamin C levels with esophageal squamous cell carcinoma was determined.

Authors Tram Kim Lam and colleagues remark that vitamin C may help protect the cells from oxidative DNA damage and other adverse effects of H. pylori infection, which is a common cause of gastric cancer. They note that H. pylori is not believed to increase the risk of esophageal squamous cell cancer, which could explain the lack of protective effect for vitamin C against this type of cancer that was observed in this study.

"This study was the largest prospective cohort study on the association between circulating vitamin C and gastric adenocarcinoma risk to date and the first prospective evaluation of the relation with esophageal squamous cell carcinoma," they announce. "Results based on our meta-analysis of prospective cohort studies suggest that plasma vitamin C is inversely associated with gastric adenocarcinoma incidence."

December 2013 Issue of Life Extension Magazine® Now Online

Life Extension Magazine November, 2013 

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