Garlic and choleterol lowering

• Allium sativum, commonly known as garlic, is a plant of the family Alliaceae. Garlic is universally used as a flavouring agent, in traditional medicine and as a functional food to enhance physical and mental health. Unique organosulphur compounds found in garlic provide its characteristic flavour, odour and most of its potent biological activity
  • intact garlic bulbs contain high amounts of gamma-glutamylcycteines and alliin, their oxidation product
    • during the manufacture of garlic products, the enzyme alliinase released rapidly lyses alliin to form allicin
      • allicin instantly decomposes to other compounds such as diallyl sulphide, diallyl disulphide, diallyl trisulphide, dithiins and ajoene
      • at the same time, gamma-glutamylcysteines are converted to S-allylcysteine (SAC) in a separate pathway
• proposed mechanisms by which garlic reduces cholesterol levels
  • there are three mechanisms proposed for the involvement of garlic in the synthesis of cholesterol
    • 1) garlic decreases cholesterol absorption in the intestine, as shown in hypercholesterolaemic rat models
    • 2) experiments using cultures of rat hepatocytes have shown that garlic inhibits the enzymes involved in cholesterol synthesis
    • 3) Borek has suggested that the cholesterol lowering effect of garlic is caused by deactivation of 3-hydroxy-3-methylglutaryl-CoA reductase, involved in the synthesis of cholesterol
• epidemiologic studies show an inverse correlation between garlic consumption and progression of cardiovascular disease (3)
• a review from 2006 stated that (3)
  • since 1993, 44% of clinical trials have indicated a reduction in total cholesterol, and the most profound effect has been observed in garlic's ability to reduce the ability of platelets to aggregate. Mixed results have been obtained in the area of blood pressure and oxidative-stress reduction. The findings are limited because very few trials have addressed these issues. The negative results obtained in some clinical trials may also have resulted from usage of different garlic preparations, unknown active constituents and their bioavalability, inadequate randomization, selection of inappropriate subjects, and short duration of trials
• however a more recent meta-analysis was not positive in the role of garlic in cholesterol lowering
  • the meta-analysis concluded that (4):
    • "..overall, the evidence suggests that intake of garlic preparations did not produce any significant beneficial effects on serum cholesterol"
    • also noted that patients on warfarin should also be made aware of a potential interaction between garlic and warfarin, which may lead to prolonged bleeding

Reference:

• 1) Spigelski D, Jones PJH. Efficacy of garlic supplementation in lowering serum cholesterol levels. Nutrition Reviews 2001; 59, 236-241.
• 2) Borek C. Garlic reduces dementia and heart-disease risk. The Journal of Nutrition 2006; 136: 810S-812S.
• 3) Rahman K, Lowe GM. Garlic and cardiovascular disease: a critical review. J Nutr. 2006 Mar;136(3 Suppl):736S-740S.
• 4) Khoo YS, Aziz Z.Garlic supplementation and serum cholesterol: a meta-analysis. J Clin Pharm Ther. 2009 Apr;34(2):133-45.