• Clouding or opacity in the crystalline lens of the eye
• Gradual loss of vision
Cataracts are white, opaque blemishes on the normally transparent lens of the eye. They occur as a result of damage to the protein structure of the lens, similar to the damage that occurs to the protein of eggs when they are boiled or fried. Cataracts are the leading cause of impaired vision and blindness in the United States. Approximately 6 million Americans have some degree of vision-impairing cataract, and among Medicare recipients, cataract surgery is the most common major surgical procedure, with nearly 1 million procedures each year.
Cataracts can be classified by location and appearance of the lens opacities, by cause or significant contributing factor, and by age of onset. Many factors may cause or contribute to the progression of lens opacity, including ocular disease, injury, or surgery; systemic diseases (e.g., diabetes); exposure to toxins, radiation, or ultraviolet and near-ultraviolet light; and hereditary disease. Aging-related cataracts (senile cataracts) are discussed in this chapter, and diabetic and galactose-induced cataracts (sugar cataracts) are discussed in the chapter “Diabetes.”
The lens of the eye is, obviously, a vital component of the visual system, owing to its ability to focus light (by changes in shape) while maintaining optical transparency. Unfortunately, this transparency diminishes with age. The majority of the geriatric population displays some degree of cataract formation. Even with normal aging there is a progressive increase in size, weight, and density of the lens.
In cataract formation, the normal protective mechanisms are unable to prevent free radical damage to the cells of the lens. The lens, like many other tissues of the body, depends on adequate levels and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, and adequate levels of the accessory antioxidants such as lutein, vitamins E and C, and selenium, to aid in prevention of damage by free radicals.1–6
Individuals with higher dietary intakes of vitamin C and E, selenium, and carotenes (especially lutein) have a much lower risk for development of cataracts.7 Several studies have shown that various nutritional supplements—multiple vitamin formulas, vitamins C and E, B vitamins (especially B12 and folic acid), and vitamin A—also offer significant protection against cataracts.8–11 Studies conducted by the Age-Related Eye Disease Study (AREDS) Research Group and others indicate that a combination of these nutrients will be likely to produce better results in the prevention of age-related macular degeneration and cataracts than any single nutrient alone, or even limited combinations of three or fewer nutrients (see the chapter “Macular Degeneration” for more information).
Lutein, a yellow-orange carotene that offers significant protection against macular degeneration, also helps protect against cataract formation.12 Like the macula, the human lens concentrates lutein. In 1992 a study showed that consumption of spinach (high in lutein) was inversely related to the risk of cataracts severe enough to require extraction.13 This initial investigation was followed by three studies that were more detailed showing that intake of lutein was inversely associated with cataract surgery (20 to 50% risk reduction).14–16 In a double-blind intervention trial, 17 patients clinically diagnosed with age-related cataracts were randomly assigned to receive dietary supplementation with either lutein (15 mg), vitamin E (100 mg), or a placebo three times a week for up to two years.17 Visual performance (visual acuity and glare sensitivity) actually improved in the lutein group, whereas there was trend toward the maintenance of visual acuity with vitamin E and a decrease with the placebo.
A high dietary intake of vitamin C from either dietary sources or supplements has been shown to protect against cataract formation.8–11 In addition to preventing cataracts, antioxidant nutrients such as vitamin C may offer some therapeutic effects. Several clinical studies have demonstrated that vitamin C supplementation can halt cataract progression and, in some cases, significantly improve vision. For example, in one study conducted in 1939, 450 patients with cataracts were started on a nutritional program that included 1 g per day of vitamin C, which resulted in a significant reduction in cataract development.1 Similar patients had previously required surgery within four years, but in this study only a small handful of the patients treated with vitamin C needed surgery, and in most there was no evidence that the cataracts had progressed over the 11-year study period.
It appears that the dosage of vitamin C necessary to increase the vitamin C content of the lens is 1,000 mg.2 The lens of the eye and active tissues of the body require higher concentrations of vitamin C. The average level of vitamin C in the blood is about 0.5 mg/dl; in the liver, spleen, and lens of the eye, the vitamin C level is increased by at least a factor of 20. In order for these concentrations to be maintained in these tissues, the body has to generate enormous amounts of energy to pull vitamin C out of blood against this tremendous gradient. Keeping blood vitamin C concentrations elevated helps the body concentrate vitamin C into active tissue by reducing the gradient. That is probably why such high dosages are required to raise the vitamin C content of the lens.
In another study, 450 patients with incipient cataracts were started on a nutritional program that included 1,000 mg per day of vitamin C, which led to a significant reduction in cataract development.3
In a large double-blind trial, 11,545 apparently healthy U.S. male physicians 50 years or older without a diagnosis of cataracts were randomly assigned to receive 400 IU of vitamin E or a placebo on alternate days and 500 mg vitamin C or a placebo per day.18 After eight years of treatment and follow-up, there was no significant difference in cataract formation in the groups. This study may have failed to show benefit because it was below the threshold of 1,000 mg per day of vitamin C.
Glutathione (GSH) is a key antioxidant found at very high concentrations in the lens. GSH plays a vital role in maintaining a healthy lens and has been postulated as a key protective factor against cataract formation. GSH functions as an antioxidant and acts as a vital coenzyme of various enzyme systems within the lens.4 Low GSH levels predispose the lens to cataract formation.
Selenium and Vitamin E
Selenium and vitamin E are antioxidants known to function synergistically. Maintaining proper selenium levels appears to be especially important because the lens antioxidant enzyme glutathione peroxidase requires selenium. Low selenium levels greatly promotes cataract formation; early studies have shown that selenium content in the human lens with a cataract is only 15% of normal levels.5
A more recent study was conducted to better examine the role of selenium in cataract formation.6 Selenium levels in the serum, lens, and fluid of the eye (aqueous humor) were determined in 48 patients with cataracts and compared with levels in matched controls. Selenium levels in the serum and aqueous humor were found to be significantly lower in the patients with cataracts (serum, 0.28 mcg/ml; aqueous humor, 0.19 mcg/ml) than in normal controls (serum, 0.32 mcg/ml; aqueous humor, 0.31 mcg/ml). However, selenium levels in the lens itself did not significantly differ between the patients with cataracts and the controls.
The most important finding of the study was the decreased level of selenium in the aqueous humor in patients with cataracts. Excessive hydrogen peroxide levels, up to 25 times normal, are found in the aqueous humor in patients with cataracts and are a key underlying factor in cataract formation. Because selenium-dependent glutathione peroxidase is responsible for the breakdown of hydrogen peroxide, it is quite obvious why low selenium levels appear to be a major factor in the development of cataracts.
As previously described, vitamin E supplementation alone does not slow the progression of cataract formation.17 A double-blind study in which vitamin E was given at a dose of 500 IU per day also found that supplementation did not slow cataract formation.19 In a seven-year trial, supplemental vitamin E (400 IU) combined with vitamin C (500 mg) and beta-carotene (15 mg) had no effect on the development or progression of cataracts.20 In order for vitamin E to function in protecting the lens against free radical damage, it requires selenium, and vice versa.
The activity of the important antioxidant enzyme SOD is lower in the human lens than in other tissues as a result of the greater ascorbate and glutathione levels in the lens. Nonetheless, SOD is a very important protector against free radical damage in the lens, and as SOD levels decline, cataracts progress. Oral supplementation is probably of little value, because it does not affect tissue SOD activity.21 Of greater value is supplementation with the trace mineral components of SOD, such as zinc, copper, and manganese. Levels of these necessary cofactors are greatly reduced in lenses with cataracts; copper and zinc levels are reduced by more than 90%, and manganese by 50%.5
Tetrahydrobiopterin is a molecule similar to folic acid and is believed to play a protective role against cataract formation by preventing oxidation and damage from ultraviolet light. This action prevents the formation of high-molecular-weight proteins in the lens. Studies of human senile cataracts have demonstrated decreased levels of tetrahydrobiopterin and pteridine-synthesizing enzymes.22 Supplemental folic acid may help compensate for this deficiency by increasing the ability to manufacture pteridines.
In order to maintain GSH in its active form, the lens requires riboflavin (vitamin B2).23,24 Deficiency of riboflavin is believed to enhance cataract formation. However, no more than 10 mg per day of riboflavin should be taken by people with cataracts, because it is a photosensitizing substance—that is, riboflavin reacts with the light to form superoxide free radicals. In animal studies, riboflavin supplementation and light have been used experimentally to induce cataracts. The evidence appears to suggest that excess riboflavin does more harm than good in patients with cataracts.
Cysteine, one of the key amino acids of GSH, has been shown to be of some aid in cataract treatment.25 N-acetylcysteine is the preferred supplemental form of cysteine.
Zinc, Vitamin A, and Beta-Carotene
Zinc, vitamin A, and beta-carotene are known antioxidant nutrients vital to the health of the eye. In particular, beta-carotene may act as a filter, protecting against light-induced damage to the fiber portion of the lens.26 However, beta-carotene supplementation on its own (50 mg on alternate days) has no impact on cataract prevention in long-term studies in either women or men.27,28
The occurrence of cataracts in rats can be slowed down by changing their diet from a commercial laboratory chow to a diet that includes flavonoids.29 Of the flavonoid-rich extracts, bilberry anthocyanosides may offer the greatest protection. In one human study, bilberry extract plus vitamin E stopped progression of cataract formation in 97% of 50 patients with senile cortical cataracts.30 Grape seed and pine bark extracts are also excellent choices in cataract prevention.
• In cataract formation, the normal protective mechanisms are unable to prevent free radical damage.
• Individuals with higher dietary intakes of antioxidants have a much lower risk for developing cataracts.
• Several clinical studies have demonstrated that vitamin C supplementation can halt cataract progression and, in some cases, significantly improve vision.
• Bilberry extract plus vitamin E stopped progression of cataract formation in 48 of 50 patients.
A number of heavy metals have been shown to have higher concentrations in both the aging lens and those with cataracts.5 The cadmium concentration is two to three times higher in cataract lenses than in lenses of age-matched controls without cataracts. Because cadmium displaces zinc from binding as a coenzyme in enzymes, it may contribute to deactivation of free radical quenching and other protective/repair mechanisms.
Other elements of unknown significance are bromine, cobalt, iridium, and nickel.5
In cases of marked vision impairment, cataract removal and lens implant may be the only alternative. As with most diseases, prevention or treatment at an early stage is most effective. Free radical damage appears to be the primary factor in the induction of senile cataracts, so avoidance of oxidizing agents and greatly increased intake of antioxidants are critical to successful treatment. Because the elderly population is especially susceptible to nutrient deficiencies, every effort should be made to ensure optimal nutrition. Wear sunglasses when outdoors. Progression of the disease process can be stopped and early lesions can be reversed. However, significant reversal of well-developed cataracts does not appear possible at this time.
Follow the guidelines given in the chapter “A Health-Promoting Diet.” Avoid fried foods, overly well-done or charbroiled meat, and other dietary sources of free radicals while increasing the consumption of antioxidant-rich foods such as legumes (high in sulfur-containing amino acids), yellow vegetables (carotenes), berries and citrus (flavonoids), and foods rich in vitamins C.
• A high-potency multiple vitamin and mineral formula as described in the chapter “Supplementary Measures”
• Key individual nutrients:
Vitamin B6: 25 to 50 mg per day
Folic acid: 800 mcg per day
Vitamin B12: 800 mcg per day
Vitamin C: 500 to 1,000 mg twice per day
Vitamin E (mixed tocopherols): 100 to 200 IU per day
Copper: 0.5 to 1 mg per day
Selenium: 100 to 200 mcg per day
Zinc: 20 to 30 mg per day
Vitamin D3: 2,000 to 4,000 IU per day (ideally measure blood levels and adjust dosage accordingly)
• Fish oils: 1,000 mg EPA + DHA per day
• Specialty supplements:
Lutein: 5 to 15 mg per day
N-acetylcysteine: 200–400 mg per day
• One or more of the following:
Bilberry (Vaccinium myrtillus) extract (25% anthocyanidin content): 160 to 240 mg day
Grape seed extract (>95% procyanidolic oligomers): 100 to 300 mg per day
Pine bark extract (>95% procyanidolic oligomers): 100 to 300 mg per day
• Some other flavonoid-rich extract with a similar flavonoid content, super greens formula, or another plant-based antioxidant that can provide an oxygen radical absorption capacity (ORAC) of 3,000 to 6,000 units or more per day