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Aging is associated with chronic diseases such as cardiovascular disease, neurological disorders, and cancer, resulting from free radical-induced damage and subsequent lipid, protein, and DNA peroxidations. Functional foods, defined as a food that has one or more compounds with biochemical and physiological functions beneficial to human health, may help prevent age-related dysfunctions and diseases by modulating certain biological mechanisms in the body. This paper reviews important mechanisms of functional foods that may improve health.
Based on extensive literature review, the author proposes four mechanisms for how functional foods might have anti-aging properties:
(1) As stabilizers of mitochondrial membranes and enhancers of mitochondrial function.
(2) As metal chelating agents.
(3) As antioxidants that decrease cell injury.
(4) As inducers of apoptosis (cell death) of preneoplastic and neoplastic cells.
Mitochondria are one of the most important sources of reactive oxygen species (ROS) produced by cell respiration. However, overproduction of ROS can damage mitochondrial DNA, which can compromise cell respiration and induce mitochondrial failure. Mitochondrial failure and massive ROS production are associated with myocardium ischemic injury and aging, as well as Parkinson's disease and Alzheimer's disease. Flavonoids (apigenin, kaempferol, luteolin, myricetin, quercetin), grape/wine polyphenols, vitamin E, clorophyllin (water-soluble chlorophyll analogue) and other phenols can protect polyunsaturated fatty acids found in membranes from oxidation, avoiding mitochondrial and other biomembrane disruptions. In addition, selenium deficiency impairs antioxidant defenses, and melatonin can prevent oxidative-induced pathologies. Other functional components of foods that may prevent or reverse mitochondrial damage are coenzyme Q10 (unbiquinone), L-carnitine, lipoic acid, nicotinamide and carnosine.
Many drugs with the potential to treat neurodegenerative disorders are metal chelators. In Alzheimer's disease, massive iron loading is responsible for neuronal damage through DNA oxidation and beta-amyloid formation. Zinc and copper are also increased in senile plaques and neuropils (network of nerve fibers) of Alzheimer's patients. Polyphenols are natural iron chelators with high antioxidant activity (quercitin, rutin, catechins, sesamol, caffeic, ferulic and tannic acids) that could decrease Alzheimer's disease risk.
Aging impairs mitochondrial function, resulting in oxidative imbalance and increased peroxidation of lipids, proteins, and DNA, and depleting antioxidant defense enzymes. Rather than increasing life span, antioxidants' benefits are related to the control of free radicals that negatively influence healthy aging. Antioxidants are thought to induce antioxidant gene expression, protect low density lipoprotein (LDL) cholesterol from oxidation and provide antiapoptotic protection of the liver, brain and heart. Many vitamins can inhibit LDL oxidation, thus protecting against heart disease. Researchers are actively seeking natural compounds in foods that have the same oxidation-inhibiting properties. Walnut polyphenols, phenolics and alpha tocopherol in extra-virgin olive oil, omega-3 fatty acids and selenium in nuts, lycopene in tomato-based foods, catechin-rich tea (Camellia sinensis), and soy isoflavones (Glycine max) all have shown some inverse relationship to risk factors for heart disease.
Functional foods also can promote vasodilatory effects by stimulation of nitric oxide production, as evidenced by studies with ginseng (Panax spp.) and black tea. Guava leaves (Psidium guajava) have been shown to help control hypertension by decreasing myocardial force and inducing atrial relaxation. Quercitin, an onion and garlic (Allium sativum) flavonoid, has been shown to increase antioxidant status and decrease arterial blood pressure and heart rate in spontaneously hypertensive rats, without having vasodilatory effects. Curcumin (Curcuma longa) has been found to inhibit rat myocardial necrosis and propolis, and grape (Vitis vinifera) extracts, which have high antioxidant activities, were found to block myocardial ischemic-reperfusion injuries in animals.
It has been postulated that a diet rich in fruits and vegetables, which is also rich in antioxidants, can enhance cognition in the elderly. Antioxidants such as tocopherols, green tea polyphenols, and phytoestrogens (resveratrol and quercetin) decrease oxidative cell injuries and inflammatory reactions, improving brain health.
A recent review of randomized human clinical trials with ginkgo (Ginkgo biloba) suggests its effectiveness in dementia and memory impairment therapy. Ginkgo extract contains quercetin, kaempferol and isorhamnetin as major constituents that can remove nitric oxide, increasing survival of hippocampal cells in the brain. German physicians have prescribed ginkgo for treatment of cognitive dysfunctions, dementia and Alzheimer's disease.
Ginseng increases antioxidant expression, induces vascular relaxation and hypotensive effects, which can benefit neurovascular domains, improving memory in animals, but clinical trials do not support its therapeutic use in humans.
Functional food biomolecules can exert anticarcinogenic effects through diverse pathways. Modulation of cytochrome P450 enzymes, antioxidant protection of DNA and induction of apoptosis of cancer cells constitute the most important anti-cancer mechanisms of functional foods. Many compounds from functional foods may suppress DNA oxidation. Increasing DNA repair (folic acid), modulating immunological response (carotenoids, vitamins C and E, selenium and zinc), inhibition of cyclooxygenase (resveratrol) and avoiding carcinogen formation and absorption (fibers) also are important anticancer properties of functional foods.
While observational and experimental research supports the protective roles of functional foods against chronic diseases, there have been negative findings. More research is needed regarding efficacy and safety parameters.
This summary, titled "How Functional Foods can Enhance Healthy Aging" by D. Webb, first appeared in the December 15, 2005 issue of HerbClip (No. 030653-294), published by the American Botanical Council (Austin, Texas). The entire article, "Review of Functional Foods, Herbs and Nutraceuticals: Towards Biochemical Mechanisms of Healthy Aging," by CKB Ferrari, can be found in Biogerontology, 2004, Vol. 5, pp. 275-289.
Reprinted by permission of the American Botanical Council (ABC). ABC is an independent, nonprofit, member-based education organization, dedicated to promoting the responsible use of herbal medicine. For more information about ABC or membership, visit www.herbalgram.org.