Pooling data from 20 randomized clinical trials indicated that antioxidant vitamin supplements were associated with significant reductions in measures of arterial stiffness, including a 4.7% reduction in the augmentation index (AIx), which has been reported as a marker of cardiovascular risk.
“The results of this meta-analysis demonstrate that supplementation with antioxidant vitamins reduces arterial stiffness, but the effect sizes are modest,” wrote the authors from Newcastle University in England and the University of Al-Mustansiriyah in Baghdad, Iraq. “The vascular protection afforded by such supplementation is enhanced in healthy, young individuals and in individuals with lower circulating concentrations of vitamins C and E.
“However, the potential public health importance of these findings remains to be tested in suitably designed personalized (or stratified) intervention studies.”
Mechanism
Writing in the Journal of Nutrition the authors noted that the vascular benefits of the nutrients may be linked to their antioxidant activity, and their ability to inactivate free radicals and maintain the integrity of the vascular wall. The nutrients may also boost the bioavailability of other beneficial compounds such as nitric oxide, which is a potent vasodilator, they added.
“However, our finding that the response in arterial stiffness to supplementation differs for each particular vitamin may suggest that each vitamin has specific effects on the vascular wall, beyond any generic antioxidant effect.”
Study details
Led by Ammar Ashor, the authors analyzed data from randomized clinical trials of antioxidant vitamins on arterial stiffness. The results indicated a statistically significant association between the supplements and a reduction in arterial stiffness for the overall data, and a trend for reduced stiffness in studies including participants with diseases.
Furthermore, the improvements did not appear to be linked to the duration of the supplementation, nor the age of the participants, added the authors.
“Despite the supporting evidence from observational studies on the beneficial effects of antioxidant vitamins on cardiovascular health, the results from RCTs testing the efficacy of antioxidant vitamins on CVD risk were discouraging,” wrote Ashor et al.
“Furthermore, these trials linked supplemental vitamin E with an increased risk of cardiovascular events and mortality. In addition to their undoubted strengths, these large RCTs have several limitations, including the potential for masking beneficial effects in particular subgroups of the population. For example, subgroup analysis revealed the beneficial effects of antioxidant vitamin supplementation on cardiovascular outcomes in individuals with low baseline plasma concentrations of vitamins in some trials.
“Our findings of larger effect sizes in sub-populations with lower baseline plasma concentrations of vitamins C and E are in line with these observations.”
Source: Journal of Nutrition
Published online ahead of print, doi: 10.3945/jn.114.195826
“Antioxidant Vitamin Supplementation Reduces Arterial Stiffness in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials”
Authors: A.W. Ashor, M. Siervo, J. Lara, C. Oggioni, J.C. Mathers