The researchers investigated the effects of adding different doses of garlic to a cholesterol-rich diet for rats, and found that beneficial effects were dependent on the dose.
"The data of the present investigation confirm that the studied commercial garlic possesses dose-dependent hypolipidemic, antioxidant, and anticoagulant properties," wrote the authors in the Journal of Agricultural and Food Chemistry (doi: 10.1021/jf058182+).
High cholesterol levels, hypercholesterolaemia, have a long association with many diseases, particularly cardiovascular disease (CVD), the cause of almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year.
The researchers, led by Shela Gornstein from the Hebrew University - Hadassah Medical School, Jerusalem, performed both in vitro and in vivo experiments to investigate the effects of a commercial garlic (Elena, Poland) on rats fed cholesterol-containing diets.
The in vitro experiments measured the polyphenol and antioxidant potentials of the commercial garlic and compared this to garlic extracts. Gornstein and her colleagues found that "the contents of dietary fibres, microelements and total polyphenols were similar to the contents in already studied garlic.".
Thirty-five male Wistar rats were divided into five equal diet groups: control (fed a basic diet), Chol (basic diet plus one per cent cholesterol), Garlic500 (Chol diet plus 500 mg garlic per kg body weight), Garlic 750 (Chol plus 750 mg garlic per kg), and Garlic1000 (Chol plus 1000 mg garlic per kg).
After four weeks, the researchers found that the Garlic500 group experienced the most benefit from the garlic supplementation. Compared to the Chol diet group, supplementation with 500 mg per kg garlic lowered total cholesterol (TC) levels by 0.6 millimoles per litre (mmol/L), LDL-cholesterol levels by 0.5 mmol/L, and total cholesterol in the liver (TCL) of 0.5 micromoles per litre. Triglyceride levels were similar.
The Garlic500 group also had the highest increase in blood clotting time and the highest antioxidant capacity.
"The above-mentioned data on serum antioxidant activity, proteins, and lipid metabolism could justify the inclusion of commercial garlic in coronary atherosclerosis-preventing diets," said Gornstein.
The researchers stress that results from animal experiments could not be automatically applied to humans and called for clinical trials with humans with atherosclerosis and high blood cholesterol levels.
Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odours that accompany the fresh bulb.
Garlic supplements are worth more than $100m (€79.5m) in the US and are also one of the biggest sellers in the UK market. According to a 1998 survey by Hartman and New Hope, garlic supplements are used twice as much as other herbal supplements.