~Cataracts, Part 3 - Nutritional Therapy
Protection from Free Radical Damage
- Protection from Free Radical Damage
- Lens Protein Protection
- Lens Metabolism Support
- Ocular Environment Support
The benefits of dietary supplements for of cataracts are widely documented. Free-radical action is directly linked to cataracts and is a major cause of damage to eyes and cataract formation.64 Numerous studies have documented the effects of supplements, including their ability to reduce free-radical damage and reverse the damage in some cases.65,66
Maintaining Glutathione Levels. A healthy eye contains glutathione in very high concentrations, whereas low levels adversely effect the eye.67 Glutathione maintains the water balance in the lens. It is synthesized in the lens (and elsewhere) and is essential to normal metabolism. Glutathione can benefit lens function by:40,57
A suggested glutathione dose is 500 mg daily.
- Preserving the physicochemical integrity of proteins in the lens33
- Maintaining action of the sodium-potassium transport pump and molecular integrity of lens fibers (protein)33
- Maintaining molecular integrity of lens fiber membranes and acting as a free radical scavenger to protect membranes and enzymes from oxidation66
- Preventing free-radical-induced photochemical generation of harmful by-products61
- Reactivating oxidized vitamin C, which improves antioxidant capability in the lens68
Vitamin C. Vitamin C (ascorbic acid) is essential for normal ocular metabolism and occurs in the lens at a concentration 30-50 times higher than blood. This concentration is second only to the central nervous system and adrenal cortex. Vitamin C is found in high concentrations in eyes of animals active during daylight hours; low concentrations are found in nocturnal animals.69 Prior to cataract formation, vitamin C concentrations significantly drop. Vitamin C provides protective benefits for the lens by:70,71
A suggested dose of vitamin C is 500 mg daily.
- Protecting the lens from photochemical oxidation72
- Helping increase levels of glutathione57
- Supporting delicate membranes regulating transport of nutrients and ions (minerals and electrolytes) into the lens60
- Protecting against damaging UV radiation and visible light73
- Protecting against superoxide radical, O2- (known to be extremely destructive in every cell)74
Vitamin B2. Vitamin B2 (riboflavin) is a required precursor to the cofactor, reduced flavin adenine dinucleotide (FADH) used by glutathione reductase, which in the lens enzymatically reduces, and thereby, activates glutathione; and makes that glutathione available for the enzyme glutathione-selenium peroxidase, which chemically reduces peroxide free radicals to harmless water. Deficiency of glutathione creates a faulty antioxidant defense system in the lens.75
Light, especially ultraviolet (UV) light, destroys riboflavin and FADH. Most B vitamins are not stored so they must be replaced daily. Riboflavin deficiency is a prime cause of photosensitivity making the eye more sensitive to UV damage. A daily dose of 50 to 150 mg of riboflavin reduces this photosensitivity.76
Selenium and Vitamin E. Low plasma levels of vitamin E increase the risk of lens opacities.77 Selenium works with alpha-lipoic acid to increase cellular concentrations of glutathione, which protects the eye lens from free radical damage.74 Taking 400–800 IU daily of vitamin E and 200–400 mcg daily of selenium is prudent to protect the lens from cataract formation and maintain overall good health.
Alpha-Lipoic Acid. Supplementation of animals with alpha-lipoic acid prevents cataract formation resulting from inhibition of glutathione synthesis. Alpha-lipoic acid reduced cataract formation by 40% and protected the lens from losing vitamins C, E, and glutathione. Unsupplemented animals lose these nutrients.78 A suggested dose of lipoic acid is 150-300 mg daily.
N-Acetyl-Cysteine and Garlic. A combination of diallyl disulfide (a major organosulfide in garlic oil) and N-acetyl-cysteine (NAC) completely prevented cataract development in animals.79 NAC assists in glutathione production because it is a source of cysteine, one of the three amino acids in this tripeptide.80 A suggested dose of NAC is 600 mg daily.
Melatonin. Melatonin is an antioxidant that could impede cataract development. In animals,81 melatonin potently inhibited cataract formation, due to free-radical scavenging or through stimulation of glutathione production. Melatonin production slows after age 40, but by age 60 virtually no melatonin is produced at a time when most cataracts develop. A suggested dose of melatonin is 500 mcg to 3 mg at bedtime.
Lens Protein Protection
Vitamin B6. Vitamin B6 (pyridoxine) is essential for amino acid and protein metabolism, absorption of vitamin B12, and proper synthesis of nucleic acids. Its coenzyme is required for many reactions of amino acids and related metabolic functions. Vitamin B6 is suggested for nutritional support for cataract patients.82 A suggested dose of vitamin B6 is 50-250 mg daily.
Acetyl-L-Carnitine. Acetyl-L-carnitine is an amino acid that maintains cellular metabolism of fatty acids. During aging, mitochondria (energy-producing organelles within the cell) begin to deteriorate, resulting in accumulation of cellular debris and eventual cell death. Acetyl-L-carnitine can diminish advanced glycation end product (AGE) damage that leads to cataract formation.83 Acetyl-L-carnitine can acetylate (deactivate) potential glycation sites on crystallins and protect them from glycation-mediated protein damage.84 A suggested dose of acetyl-L-carnitine arginate is 3-4 capsules daily.
Aminoguanidine. Aminoguanidine inhibits advanced glycation end products (AGEs) and may treat diabetic cataracts. In moderately and severely diabetic rats, aminoguanidine inhibited cataracts only in moderately diabetic rats.85 It is importance to maintain control over blood sugar levels, so that antiglycating agents such as aminoguanidine can protect against cataract. A suggested dose of aminoguanidine is 300 mg daily.
Note: Although aminoguanidine has been safely used throughout the world for decades, clinical experience is limited in the United States. Aminoguanidine has not been approved by the U.S. Food and Drug Administration. Aminoguanidine should be taken under the supervision of a physician. It can inhibit vitamin B6 uptake so co-administration of B6 is suggested.
Note: The Alteon Corporation (USA) has aminoguanidine (Pimagidine®) in stage III trials for diabetes.
Lens Metabolism Support
Bioflavonoids. Bioflavonoids are powerful inhibitors of the enzyme aldose reductase.68 If aldose reductase activity falls, sorbitol is not synthesized. This reduces the accumulation of water in the lens.86 The bioflavonoids quercetin, myrcetin, and kaempferol (from limes) specifically inhibit diabetic cataracts.71 Gingko is a widely used flavonoid that maintains microcirculation to the eye and inhibits free radicals.87 A suggested dose of gingko biloba is 120 mg daily.
Inositol. Inositol nicotinate is a B vitamin that occurs in high concentrations in the lens. Inositol exhibits antioxidant property resulting in the quenching of reactive oxygen and scavenging of glucose.88 Inositol works best taken with B complex vitamins. A suggested dose of inositol is 250 mg daily.89
Carnosine. Carnosine inhibits formation of advanced glycation end products (AGEs) and protects normal proteins from the toxic effects of existing AGEs.90,91 Eye drops containing N-acetyl-L-carnosine can delay vision senescence in humans: effective in 100% of primary senile cataract cases and 80% of mature senile cataract cases. N-acetyl-L-carnosine enter the aqueous and lipid parts of the eye and prevent and repair light-induced breaks to DNA strands.92 N-acetyl-L-carnosine eye drops are approved for human use in Russia for the treatment of many eye diseases. Brite Eyes II is an advanced eye formula that contains 1% N-acetyl-L-carnosine in a soothing eye drop. A suggested oral dose of carnosine is 500-1000 mg daily.
Ocular Environment Support
Carotenoids. Carotenoids are fat-soluble, yellowish pigments found in some plants, algae, and photosynthetic bacteria. Carotenoids are light-gathering pigments that provide protection from the toxic effects of oxygen free radicals and singlet oxygen which are generated in the presence of light and oxygen.93 Lutein and zeaxanthin are carotenoids found in high concentrations in the macula of the retina.94,95 Lutein and zeaxanthin protect the eye from age-related macular degeneration and cataract formation.65 Lutein is derived from dark green leafy vegetables (spinach, broccoli, kale, and collard greens). Zeaxanthin is found in yellow fruits and vegetables (corn, peaches, and mangoes). Suggested doses are 5 mg of zeaxanthin and 10 mg of lutein.
Coenzyme Q10. Coenzyme Q10 (CoQ10) is an antioxidant that provides protection from free radical damage in the eye.96 A combination of antioxidants including CoQ10, acetyl-L-carnitine, polyunsaturated fatty acids (PUFAs), and vitamin E improved mitochondrial function (linked to age-related macular degeneration) in retinal pigment epithelium.83 Mitochondrial dysfunction in lens epithelial cells and superficial fiber cells of the eye may lead to oxidative stress and cataract formation. Mitochondrial dysfunction occurs throughout the body and produces damaging reactive oxygen species thought to cause aging and disease.97 A suggested dose of CoQ10 is 100-200 mg daily.
Potassium and Magnesium. A lens with cataracts has decreased concentrations of potassium and magnesium.98 Potassium and magnesium are often deficient in aging humans. Supplementation with 400 mg of elemental potassium and 800 mg of elemental magnesium increases availability of these minerals to the lens and protects the arterial system.98
Gingko and Bilberry. Gingko biloba extract is an antioxidant, increases circulation to the optic nerve75 and has exhibit potential anti-cataract ability.87 Bilberry (from Vaccinium myrtillus fructus) is a proanthocyanidin historically used for eye conditions, including glaucoma, cataracts, macular degeneration, diabetic retinopathy, and retinitis pigmentosa.75 Gingko biloba and bilberry may restore microcapillary circulation.83 Suggested doses are Gingko biloba, 120 mg daily, and bilberry, 100 mg daily. After taking Ginkgo and bilberry for a month; taking 400 mcg of selenium, 500 mg of glutathione, and 300 mg of alpha-lipoic acid daily has been suggested.
FUNCTIONAL AND PRACTICAL MEDICINE
- Free Radical Reduction
- Protection from Free Radicals: The Glutathione Mechanism
- Lens Protein Protection and Cellular Metabolism Maintenance
- Maintaining a Healthy Ocular Environment
Treatment for cataracts is reactive: when cataracts adversely impact vision, they are surgically removed and replaced with an implanted lens. Cataract surgery is very effective and has a high success rate. Nutritional therapy can prevent the onset of cataracts, particularly because proven anti-cataract drugs are not available.62
Intervention strategies should address the underlying causes of cataracts: oxidative stress, free radical production, the breakdown and aggregation of lens proteins, dysfunction of metabolism in the lens, and inability to maintain a healthy ocular environment. Nutritional therapy is available for each of these underlying causes.
Metabolic Changes and Cataract. An aging lens undergoes metabolic changes that predispose it to cataracts. Some metabolic changes occur from reduced oxygen and nutrient supply which increases eye vulnerability to free-radical damage. The eye is protected by cellular antioxidants: glutathione and vitamin C. Healthy eyes are protected from free radical damage by a mechanism that produces and recycles antioxidants in the eye that neutralize free radicals. Cataract formation is associated with a breakdown in the mechanism that regulates utilization of glutathione and vitamin C and/or decreases their concentration in the lens and surrounding structures.58
Hydrogen Peroxide and Cataract. Cataract formation is initiated by the free radical hydrogen peroxide found in the aqueous humor.99 Hydrogen peroxide oxidizes glutathione, or conversely, glutathione chemically reduces hydrogen peroxide, ultimately damaging the energy-producing system of the eye and allowing sodium to leak into the lens. Excess sodium attracts water to maintain osmolality, which initiates the edema phase of a cataract. Normal body heat in the lens catalyzes oxidation of the lens' proteins, which become opaque and insoluble (similar to the process by which egg protein changes from clear to opaque upon cooking). Free radicals break down fatty acids in membranes and lens protein fibers, generating more free radicals. This cross-links (or denatures or breaks down) the laminate-like structural proteins inside the lens capsule. The lens capsule can swell or shrink (dehydrate) and these changes in pressure breaks lens fiber membranes, forming microscopic spaces that trap water and debris.101
Metabolism Support: Key Components
The key components are glutathione and vitamin C. In particular, glutathione is required to protect mature lens fiber cells from free radical damage. Vitamin C (ascorbic acid) protects the lens from oxidative damage.99,100
Protection from Free Radicals: The Glutathione Mechanism
Nutritional supplements reduce the risks of developing cataracts and slow or reverse cataract growth.101 Blood circulation within the eye is minimal so supplementing with oral nutrients is challenging.102 The most important nutrients maintain or stimulate antioxidant mechanisms utilizing glutathione and include vitamins C, B2, E, selenium, alpha lipoic acid, melatonin, N-acetyl-cysteine with garlic, and glutathione. Decreased glutathione and vitamin C are associated with cataracts.103,104
Lens Protein Protection and Cellular Metabolism Maintenance
Proteins deep in the lens are generated during embryogenesis and must retain functionality for many decades. The inability to maintain protein stability over time leads to formation of a nuclear cataract (the predominant form). Once the lens forms (embryologically), proteins are only synthesized in the outermost fiber cells close to the lens surface.79 Accumulated damage to the proteins causes loss of enzymatic activity and increases the likelihood of protein aggregation, a component of cataract formation.20
The glycation (glycosylation) process can change (denature) lens proteins and significantly contribute to diabetic cataract formation and retinopathy. Glycation occurs when proteins react with sugars and form advanced glycation end products (AGEs), essentially, proteins strongly (covalently) bind to sugars, compromising the function of that protein. AGEs are biochemically altered proteins, DNA, and lipids with altered physiological properties.105
Nutritional supplements that may decrease breakdown of lens proteins and help maintain cellular metabolism include vitamin B6, acetyl-L-carnitine, aminoguanidine, bioflavonoids, inositol, and carnosine.
Maintaining a Healthy Ocular Environment
Cataract formation is connected to the aging process, associated with increased oxidative stress, and a consequence of free radical attacks, and reduced efficiency of metabolic processes. The lens provides an environment where these processes proliferate at a rate faster than that in other parts of the body. The lens consists of multiple layers of cells without the usual cellular organelles for energy production and other regenerative mechanisms for cellular biostability.40 Lens fiber cells dependent upon a small number of lens surface cells and surrounding cells for support. Over time these support mechanisms require increased nourishment and more antioxidants.50
Decrease efficiency in these supportive mechanisms is inevitable in aging, but it is possible to counteract these age-related processes by maintaining a healthy ocular environment with optimally maintained levels of antioxidant and cellular metabolism to ensure optimal lens function.64 Aging and oxidative stress, in particular, affects the entire body. Free radical proliferation can be minimized in the eye through proper diet and lifestyle, positively affecting overall health.
Maintaining a healthy ocular environment begins by avoiding common lifestyle and environmental risks that promote eye disease, cataract development in particular, and by following dietary and nutritional recommendations that support overall eye health.
Risk Factor Avoidance
Environmental risk factors to avoid include smoking, excessive alcohol consumption, excessive exposure to sunlight, especially UV radiation, and exposure to X-rays and gamma radiation.
Recommendations include increased consumption of vegetables and fruits, "good fats" found in oily fish (e.g., salmon and tuna), whole grains, and legumes, and minimal consumption of saturated fats and cholesterol.106 Consuming foods rich in the carotenoids lutein and zeaxanthin is especially important.
Nutritional Supplement Support
Important nutritional supplements for maintaining healthy eyes include coenzyme Q10 (CoQ10), potassium, magnesium, Ginkgo, bilberry, and taurine.
CoQ10. CoQ10 is an antioxidant that improves mitochondrial function in the retina. This function is linked to age-related macular degeneration.96,83
Potassium and magnesium. Decreased potassium and magnesium concentrations are found in a lens with cataract.
Gingko biloba and bilberry. Gingko biloba and bilberry support restoration of microcapillary circulation to the eye by protecting and strengthening ocular blood vessels.75 Gingko and bilberry can be effectively combined with daily doses of 400 mcg of selenium, 500 mg glutathione, and 300 mg of lipoic acid.33,75 Molecular and cellular assessment of gingko biloba extract as an ophthalmic drug determined it was an excellent antioxidant that readily scavenged free radicals, inhibited oxidative damage to proteins, and protected cells from light-mediated stress and DNA breakage, but did not alter endogenous antioxidant enzyme activity or protect against phototoxicity. It significantly retarded lens opacification in cataracts induced in rats.87
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