Dried, powdered garlic products should be standardized to contain 1.3% alliin (the allicin precursor) or have an allicingenerating potential of 0.6%. Enteric-coated formulations are recommended to minimize degradation of the active substances. A daily dose of 600–900 mg/d of powdered garlic is most common. This is equivalent to one clove of raw garlic (2–4 g) per day. A garlic bulb can contain up to 1.8% alliin. Doses of AGE most often range from 600 to 1800 mg/d, but doses up to 7200 mg daily have been safely used in clinical trials for up to 6 months.
Ginkgo biloba extract is prepared from the leaves of the ginkgo tree. The most common formulation is prepared by concentrating 50 parts of the crude leaf to prepare one part of extract.
The active constituents in ginkgo are flavone glycosides and terpenoids including ginkgolides A, B, C, and J, and bilobalide.
1. Cardiovascular effects—In animal models and some human studies, ginkgo has been shown to increase blood flow, reduce blood viscosity, and promote vasodilation, thus enhancing tissue perfusion. Enhancement of endogenous nitric oxide effects (see Chapter 19) and antagonism of platelet-activating factor have been observed in animal models.
Ginkgo biloba has been studied for its effects on mild to moderate occlusive peripheral arterial disease. Among 11 randomized, placebo-controlled studies involving 477 participants using standardized ginkgo leaf extract (EGb761) for up to 6 months, a nonsignificant trend toward improvements in pain-free walking distance (increase of 64.5 meters) was observed (P = .06). The authors concluded that the standardized extract lacked benefit for this indication.
The Ginkgo Evaluation of Memory (GEM) study and the recently published GuidAge study evaluated cardiovascular outcomes as well as incidence and mean time to Alzheimer’s dementia associated with the long-term use of ginkgo for 5–6 years in approximately 3000 elderly (age ≥70) adults with normal cognition or mild cognitive impairment. Daily use of 240 mg/d EGb761 did not affect the incidence of hypertension or reduce blood pressure among persons with hypertension or prehypertension. No significant effects in cardiovascular disease mortality, ischemic stroke or events, or hemorrhagic stroke were observed.
2.
Metabolic effects—Antioxidant and radical-scavenging properties have been observed for the flavonoid fraction of ginkgo as well as some of the terpene constituents. In vitro, ginkgo has been reported to have superoxide dismutase-like activity and superoxide anionand hydroxyl radical-scavenging properties. The flavonoid fraction has also been observed to have antiapoptotic properties. In some studies, it has also demonstrated a protective effect in limiting free radical formation in animal models of ischemic injury and in reducing markers of oxidative stress in patients undergoing coronary artery bypass surgery.
3.
Central nervous system effects—In aged animal models, chronic administration of ginkgo for 3–4 weeks led to modifications in central nervous system receptors and neurotransmitters. Receptor densities increased for muscarinic, α2, and 5-HT1a receptors, and decreased for β adrenoceptors. Increased serum levels of acetylcholine and norepinephrine and enhanced synaptosomal reuptake of serotonin and dopamine have also been reported. Additional possible effects include inhibition of amyloid-beta fibril formation and protective effects of Egb761 on hippocampal neurons against cell death induced by beta-amyloid.