A pilot study of garlic consumption shows no significant effect on markers of oxidation or sub-fraction composition of low-density lipoprotein including lipoprotein(a) after allowance for non-compliance and the placebo effect

Our aim was to define any effects of confirmed garlic supplementation on the resistance of low density lipoprotein (LDL) to oxidation, on LDL sub-fraction composition including levels of lipoprotein(a), and on levels of circulating antibody to oxidised LDL, variables of interest in relation to cardiovascular risk. Additional tests were performed on samples collected from a double blind, randomised 6-month parallel trial in which 900 mg Kwai garlic or placebo was taken by moderately hypercholesterolaemic volunteers. Final data was analysed for 20 garlic and 11 placebo subjects with compliance of at least 75% as determined by repeat tablet counting. EDTA plasma stabilised by sucrose was stored at - 70 degrees C for up to 12 months. Lipids and apolipoproteins were determined by standard methods, lipoprotein(a) by an ELISA method and LDL fraction composition by non-gradient gel electrophoresis. Oxidative resistance of LDL purified after isolation by density gradient centrifugation was assessed from oxidative resistance to copper ions determined spectrophotometrically, antibodies to oxidised LDL were determined by a microtitre plate assay and vitamin E content of plasma by HPLC. Overall lipid/lipoprotein profiles including Lipoprotein(a) were unchanged as with the parent group. LDL composition showed a trend to less dense material in both placebo and garlic groups, all differences not significant. Lag time as a marker of oxidative resistance also increased in both groups, without change in vitamin E content, all differences not significant and consistent with a placebo effect. Levels of antibodies to oxidised LDL were unchanged. The results of this study do not support the hypothesis that dietary garlic supplementation decreases the susceptibility of isolated LDL to oxidation and that patterns of LDL fractions in plasma might be involved. Levels of lipoprotein(a) in plasma were also not changed. Other mechanisms of cardiovascular benefit are however not excluded. (C) 1999 Elsevier Science B.V. All rights reserved.