Garlic (Allium sativum) is perennial herb that belongs to the same groups as onions, shallots, chives and leeks. Garlic is thought to have originated from India and central Asia, and was probably introduced to Britain by the Romans. Garlic produces a bulb that is divided into smaller segments called cloves and these have some interesting medicinal properties when consumed. The use of garlic medicinally can be traced back to the earliest historical records. The cloves of garlic can be eaten raw, cooked, dried, or the essential oils can be removed through mechanical pressing to create an essential garlic oil. Disrupting the cells mechanically through chewing, crushing or slicing causes a number of odourless organosulphur compounds to come into contact with converting enzymes that synthesise a number of short lived volatile compounds that give garlic its distinctive pungent smell and taste. Garlic also contains a number of steroidal saponins that may contribute towards its medicinal properties.
Garlic has a number of important medicinal properties, including anti-inflammatory, antioxidant and anti-helminthic properties. However, perhaps the most well studied of the health effects of garlic is its ability to improve blood lipid profiles. For example, in one study1, the effects of 0.25 mg of essential garlic oil per kg of body weight was investigated in individuals with coronary heart disease. The subjects were chosen because they had high levels of plasma cholesterol and triglycerides. Following 6 to 10 months of supplementation with the garlic oil, the researchers reported a significant decrease in serum cholesterol levels of between 17 and 18 %. In particular, low density lipoprotein levels (LDL) decreased significantly, and high density lipoprotein (HDL) levels showed a trend to increase. Therefore the patients experienced beneficial changes in their LDL to HDL ratios that would indicate their health had improved. The researchers also reported that serum triglycerides decreased by around 20 % with garlic supplementation.
These results support a growing body of evidence that suggests that garlic is beneficial at producing blood lipid modifying effects. The reason for the efficacious cholesterol modifying properties of garlic are not fully understood, but may relate to the presence of organosulphur compounds or the saponins in the herb. Garlic also possesses significant antioxidant capacity, and this may benefit cardiovascular system by protecting the endothelial production of nitric oxide, thereby allowing correct endothelial relaxation in response to blood flow. This is likely the mechanisms by which garlic can lower blood pressure. Chemicals in garlic also show fibrinolytic properties, as well as the ability to cause reductions in the adhesiveness of platelets, conferring additional beneficial properties on the herb with regard to cardiovascular health. Garlic is particularly beneficial in those at high risk of cardiovascular disease, which explains that large effects seen in the subjects with coronary heart disease in this study.
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