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Garlic for hypercholesterolemia: Update


Clinical bottom line:

Relatively small trials produced a 6% reduction in total cholesterol with garlic therapy in patients with hyperlipidemia. Odour and gastrointenstinal adverse effects were reported. Methodological problems included that of odour disclosing the treatment, and confounding caused by dietary factors.

Systematic review

Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesterolemia. A meta-analysis of randomised clinical trials. Annals Internal Medicine 2000; 133(6): 420-429.

Date review completed : November 1998

Number of trials included : 13

Number of patients : 796 total

Control group : Placebo

Main outcomes : Mean change (from baseline) in total cholesterol.

Inclusion criteria were randomised, double blind, placebo controlled trial which assessed garlic in patients with mean total cholesterol level of 5.17 mmol/L (200 mg/dL), and reported total cholesterol as an end point.

Medline, Embase, AMED, BIOSIS, CISCOM and the Cochrane Library were searched using relevant key words. Manufacturers of garlic monopreparations were contacted for additional studies (published or unpublished). No language restrictions were made and authors were contacted if additional information was required. Two reviewers, who were blind to the authors, institutions and publication details of the studies, extracted relevant data. The quality of the reports was assessed using a three-item, five point scale. Information was pooled in a meta-analysis and weighted mean difference, with 95% confidence intervals, was calculated.

Findings

Thirteen trials were included in the meta-analysis. All compared garlic (mainly 600-900 mg per day) with placebo over 8-24 weeks. Mean baseline total cholesterol values ranged between 5.78 ± 1.06 mmol/L and 7.72 ± 3.37 mmol/L in the garlic groups, and between 5.62 ± 0.70 mmol/L and 7.64 ± 1.55 mmol/L in the placebo groups. Overall, garlic was significantly better at reducing total cholesterol than placebo; weighted mean difference 0.41 (95% confidence intervals 0.15 to 0.66) mmol/L. This represents a 5.8% reduction from baseline with garlic.

Sensitivity analyses

Similarity of study methods

Five of the trials assessed standardised garlic powder 900 mg per day, over 12 or 24 weeks (566 patients). All studies controlled for dietary factors. There was no significant difference between garlic and placebo; weighted mean reduction in total cholesterol from baseline was 0.19 (95% CI -0.01 to 0.39).

Study quality

Six studies had a quality score of 4 or 5. All controlled for dietary factors. When information was pooled from these studies (600 patients) there was no significant difference in total cholesterol with garlic compared with placebo; the weighted mean reduction in total cholesterol from baseline was 0.11 (95% CI -0.01 to 0.35) mmol/L.

Other lipids

Five studies also presented information on LDL and HDL cholesterol levels. There was no significant difference in LDL or HDL cholesterol with garlic compared with placebo. The weighted mean differences were 0.17 (95% CI -0.01 to 0.35) mmol/L and 0.07 (-0.10 to 0.2) mmol/L respectively.

Adverse effects

Few adverse effects were reported. Odour and gastrointestinal symptoms (e.g. diarrhoea, epigastric burning) were reported with garlic.

Comment

Mainly small studies showed a 6% reduction in total cholesterol levels with garlic. This result was not upheld when studies of similar design, or highest methodological quality were assessed alone. There are methodological issues to raise about these trials. Garlic odour was reported in some studies; this could have revealed the identity of the treatment. In others patients were additionally given dietary advice, or no dietary controls were made. These factors could also influence the results obtained. One study assessed children with familial hypercholesterolemia, a condition which is difficult to treat. Overall, the review shows that the benefits of garlic are small and probably do not exceed those reported by dietary control alone [1]. At present, there is not sufficient benefit to warrant treatment with garlic. Greater control of total cholesterol can be obtained with statins.

Further reading

1. Tang JL, Armitage JM, Lancaster T et al. Systematic review of dietary intervention trials to lower blood total cholesterol in free-living subjects. BMJ 1998; 316: 1213-20.

Identifier 8003 GARLIC AND HYPERLIPIDEMIA UPDATE: Apr-2001