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Vitamins and abdominal aortic aneurysm.

INTRODUCTION
To summarize the association of vitamins (B6, B12, C, D, and E) and abdominal aortic aneurysm (AAA), we reviewed clinical studies with a comprehensive literature research and meta-analytic estimates.


EVIDENCE ACQUISITION
To identify all clinical studies evaluating the association of vitamins B6/B12/C/D/E and AAA, databases including MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched through April 2015, using Web-based search engines (PubMed and OVID). For each case-control study, data regarding vitamin levels in both the AAA and control groups were used to generate standardized mean differences (SMDs) and 95% confidence intervals (CIs).


EVIDENCE SYNTHESIS
Pooled analyses of the 4 case-control studies demonstrated significantly lower circulating vitamin B6 levels (SMD, -0.33; 95% CI, -0.55 to -0.11; P=0.003) but non-significantly lower vitamin B12 levels (SMD, -0.42; 95% CI, -1.09 to 0.25; P=0.22) in patients with AAA than subjects without AAA. Pooled analyses of the 2 case-control studies demonstrated significantly lower levels of circulating vitamins C (SMD, -0.71; 95% CI, -1.23 to -0.19; P=0.007) and E (SMD, -1.76; 95% CI, -2.93 to 0.60; P=0.003) in patients with AAA than subjects without AAA. Another pooled analysis of the 3 case-control studies demonstrated significantly lower circulating vitamin D (25-hydroxyvitamin D) levels (SMD, -0.25; 95% CI, -0.50 to -0.01; P=0.04) in patients with AAA than subjects without AAA. In a double-blind controlled trial, 4.0-year treatment with a high-dose folic acid and vitamin B6/B12 multivitamin in kidney transplant recipients did not reduce a rate of AAA repair despite significant reduction in homocysteine level. In another randomized, double-blind, placebo-controlled trial, 5.8-year supplementation with α-tocopherol (vitamin E) had no preventive effect on large AAA among male smokers.


CONCLUSIONS
In clinical setting, although low circulating vitamins B6/C/D/E (not B12) levels are associated with AAA presence, vitamins B6/B12/E supplementation may not reduce AAA incidence.