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Garlic for hyperlipidaemia



Clinical bottom line: Small, randomised studies of relatively poor quality showed modest reductions in serum lipids with garlic therapy, but not all patients recruited in the trials had hyperlipidaemia. More recent trials have shown no significant benefit of garlic therapy over placebo.


Systematic review:

Silagy C, Neil A. Garlic as a lipid lowering agent: a meta-analysis. J Royal Coll Phys London 1994; 28(1): 39-45.

Date review completed: July 1992

Number of trials included: 16

Number of patients: 952 total

Control groups: placebo, avoidance of garlic in diet, bezafibrate / diuretic plus reserpine.

Main outcomes: change in serum lipids (mmol/l) from baseline value.

Inclusion criteria were randomised controlled trials which assessed the effect of garlic on serum lipids for more than four weeks. Datastar, MEDLINE and the Alternative Medicine database were searched for relevant studies. Reference lists and reviews were checked for additional citations. Unpublished data was sought from manufacturers of garlic preparations and authors. Authors were also contacted for additional information about specific trials. No language restrictions were made. Study quality was assessed. For cross-over trials, information was extracted for the first treatment phase only. Pooled data wee used to calculate the effect size with 95% confidence intervals and Mantel-Haenszel heterogeneity tests were conducted.

Findings:

Sixteen randomised controlled trials (RCTs) were included. The quality of the studies was generally poor, though the one study which compared garlic powder with bezafibrate scored the maximum number of points.

Non-powder preparations:

Five RCTS assessed garlic versus placebo or no garlic control in 205 patients over 2-10 months. Two studies were double blind, two were open label and one was single blind. The daily dose of garlic varied: 10 g fresh, 0.25 mg/Kg or 18 mg oil, dose was not stated for garlic extract. Baseline cholesterol was between 5.45-7.92 mmol/l. Total cholesterol was reduced with garlic therapy, 0.99 mmol/l (95% C.I. 0.83 to 1.16). No further analyses were conducted because the data were heterogeneous.

Powder preparations:

Eleven RCTs assessed either dried/spray garlic 600-900 mg/day over 1-6 months. Control groups were placebo (10 studies) and a reserpine/diuretic combination (one study). The 10 placebo controlled studies were double blind; the other was single blind. Baseline cholesterol was between 4.72-7.59 mmol/l; three did not state the baseline value. Powdered garlic reduced total cholesterol by 0.51 mmol/l (95% C.I. 0.33 to 0.69). Greater improvements in serum cholesterol were shown at three months than at one month. A significant reduction, 0.31 mmol/l (95% C.I. 0.14 to 0.49), in serum triglyceride was shown in placebo comparisons, but the reduction in HDL cholesterol was not significant, 0.04 mmol/l (95% C.I. 0.11 to 0.03). Both garlic and bezafibrate (994 patients) were effective for triglyceride and HDL cholesterol levels; there was no significant difference between the two treatments.


Adverse effects

Adverse effects, including odour, were uncommon. The likelihood of odour was almost four times greater, 3.8 (95% C.I. 1.8 to 7.8), with the odour-controlled dried garlic tablets than with placebo.

 

Comment

There appears to be some evidence of a reduction in serum lipid levels with garlic therapy. Overall a 12% greater reduction was shown with any garlic therapy compared with placebo in this meta-analysis. A previous meta-analysis [1] reported a 9% reduction. More recent RCTs have shown a more conservative effect or no significant benefit of garlic over placebo [2-6].

Further reading

1. Warshafsky S, Kamer RS, Sivak SL. Effect of garlic on total serum cholesterol. A meta-analysis. Ann Intern Med 1993; 119: 599-605.

2. Neil HA, Silagy CA, Lancaster T, Hodgeman J, Vos K, Moore JW, Jones L, Cahill J, Fowler GH. Garlic powder in the treatment of moderate hyperlipidaemia: a controlled trial and meta-analysis. J Royal Coll Phys London 1996; 30(4): 329-334.

3. Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism: a randomized controlled trial. JAMA 1998; 279: 1900-1998.

4. Isaacsohn JL, Moser M, Stein EA et al. Garlic powder and plasma lipids and lipoproteins: a multicenter, randomized, placebo-controlled trial. Arch Intern Med 1998; 158: 1189-1994.

5. McCrindle BW, Helden E, Conner WT. Garlic extract therapy in children with hypercholesterolemia. Arch Pediatr Adolesc Med 1999; 152: 1089-1994.

6. Superko HR, Krauss RM. Garlic powder, effect on plasma lipids, postprandial lipemia, low-density lipoprotein particle size, high-density lipoprotein subclass distribution and lipoprotein (a). J Am Coll Cardiol 2000; 35: 321-2000.

 


Related topics

Identifier

AT054 - 5962 GARLIC FOR HYPERLIPIDAEMIA: Jul-2000