Oral doses of vitamin C greater than 500 milligrams per day may boost the health of the endothelium - the thin layer of cells lining the blood vessels – and boost overall heart health for people who need it the most, according to a meta-analysis of 44 clinical trials.
Scientists from Newcastle University in England report that endothelial function was significantly improved by vitamin C supplements in people with diabetes, atherosclerosis, and heart failure. No effects were observed in health volunteers, however, they reported in Atherosclerosis .
The endothelium performs many functions including maintaining the suppleness of blood vessels and regulating the activity of neutrophils, white blood cells that form a key part of the immune system.
Dysfunction in the endothelium leads to arteries with little suppleness, raising the risk of high blood pressure (hypertension), and arteries that are chronically inflamed, leading to an overabundance of adhesion molecules.
“To our knowledge, this is the first systematic review and meta-analysis evaluating the effect of supplemental vitamin C on endothelial function in human adults,” wrote the researchers, led by Ammar Ashor.
“Data synthesis from 44 RCTs demonstrated that supplemental vitamin C was associated with significant improvement of endothelial function in subjects with cardio-metabolic disorders.”
The Newcastle-based scientists pooled data from 44 clinical trials involving 1129 participants and found that, overall, vitamin C supplements were associated with beneficial effects on endothelial function.
Further crunching of the numbers indicated that the benefits appeared limited to people with atherosclerosis, diabetes, and heart failure.
Commenting on a potential mechanism of action, the researchers noted that both oxidative damage and vascular inflammation are known to affect endothelial function, while nitric oxide (NO) – a potent vasodilator – is a major player in preserving endothelial function.
“In addition to its direct reactive oxygen species (ROS)-quenching function, the beneficial effects of vitamin C on endothelial function may be related to the increase in NO bioavailability as a result of the enhanced efficiency of the enzymatic and non-enzymatic synthetic NO pathways and reduced cross-reactivity with ROS,” they said.
“These results support the idea that vitamin C may be a useful nutritional intervention for the secondary prevention of cardiovascular diseases.
“However, future RCT to test the effect of supplementary vitamin C on major cardiovascular outcomes (morbidity and mortality) should recruit those likely to benefit i.e. non-smoking patients with diabetes, atherosclerosis or heart failure,” they concluded.
Volume 235, Issue 1, Pages 9-20
“Effect of vitamin C on endothelial function in health and disease: A systematic review and meta-analysis of randomised controlled trials”
Authors: A.W. Ashor, J. Lara, J.C. Mathers, M. Siervo