Can Diet, Lifestyle Changes Really Prevent Cataracts?

The mounting, and controversial, evidence that modifying risk factors can prevent lens opacities.

BY Sean McKinney

Like AMD, cataract has drawn the focus of researchers trying to determine if vitamins, nutrition and lifestyle changes can forestall the need for surgery. The latest evidence provides mixed results, indicating the possibility of strong associations in some studies and findings to the contrary in others. Among commonly cited risk factors are smoking, diabetes, poor nutrition, advanced age, female gender and large drusen.

The findings raise the issue of what, if anything, ophthalmologists should tell their patients to help them prevent cataract formation. “We should counsel patients on modifiable risk factors, such as smoking,” says Rohit Varma, MD, MPH, professor and department chairman at Illinois Eye and Ear Infirmary, University of Illinois at Chicago. “We can also consider risk factors that are not definitive at this point, possibly by examining patients every year or six months, particularly if their vision is reduced or if they are not able to perform daily activities,” he says.

This article reviews the evidence on the role diet and nutrition play in cataract prevention and development.

Assessing Effects of Vitamins

To assess the possible effects of high-dose vitamins and minerals on AMD and cataracts, the National Eye Institute sponsored the Age-Related Eye Disease Study (AREDS), which concluded in 2001. AREDS, the first prospective, randomized, multicenter, double-masked, placebo-controlled trial of diet and eye disease, was designed in part to evaluate the effects of high doses of antioxidants on the development and progression of cataract and vision loss.

AREDS results showed that high levels of antioxidants and zinc had no significant effect on the development or progression of cataract.¹ The follow-up to this study, AREDS2, is evaluating if risk factors associated with cataracts are affected by oral supplementation with macular xanthophylls and omega-3 long-chain polyunsaturated fatty acids when compared to placebo. Results are expected in the second quarter this year.²

Continuing focus on nutrition

AREDS2 is only one of several studies that have recently focused on nutrition and cataracts.

When he was professor of ophthalmology and preventive medicine at Doheny Eye Institute, University of Southern California, Dr. Varma joined other researchers in evaluating risk factors for cortical, nuclear, posterior subcapsular (PSC) and mixed-lens opacities. The Los Angeles Latino Eye Study, published last year, evaluated the risk factors of 5,945 Latinos in Los Angeles age 40 or older.³ The major findings included:

► Cortical-only opacities in 468 participants. Independent risk factors included older age, higher hemoglobin A1C levels and history of diabetes mellitus.

► Nuclear-only lens opacities in 217 participants. Independent risk factors included older age, smoking and myopic refractive error.

► PSC-only opacities in 27 participants. Independent risk factors included higher systolic blood pressure and history of diabetes.

► Mixed-lens opacities in 364 participants. Independent risk factors included older age, myopic refractive error, history of diabetes, higher systolic blood pressure, female gender and presence of large drusen.

Delineating the Risk Factors

The researchers concluded that identifying risk factors could help reduce the incidence of lens opacities and associated vision loss. “The risk factors that are modifiable, including improved control of diabetes and/or smoking cessation, have the potential to reduce the development of these types of cataracts,” says Dr. Varma. He summarized the latest thinking:

► Age. AREDS found an association between lens opacity and aging.⁴ Age also represents increased cumulative exposure to numerous risk factors, including environmental factors such as ultraviolet B light radiation or oxidative damage.⁵

► Diabetes mellitus and elevated HbA1c. Besides the Latino Eye Study, the Barbados and Beaver Dam Eye studies also reported significant associations between diabetes and prevalent or incident cortical, nuclear and PSC lens opacities.^6,7 Likewise, Dr. Varma notes, a 13-year-old French study reported significant associations between diabetes and cortical, PSC and mixed lens opacities.⁸

Mechanisms of Lens Opacification

Previously studied mechanisms underlying the relationship between diabetic hyperglycemia and lens opacification included direct glycation of lens proteins and sugar alcohols formed via the aldose reductase pathway and exerting a direct toxic effect on lens fibers. “Another possible mechanism is the activation of calpains by elevated levels of calcium in patients with diabetes mellitus, leading to insolubilization of lens crystallins and the subsequent opacification of the lens,” Dr. Varma says. “Our findings reinforce this relationship.”

► Smoking. Besides the Los Angeles Latino Eye Study, a number of trials have reported a specific association between smoking and nuclear lens opacities. “Our speculation is that this association likely involves oxidative lens damage, possibly explained by reduced antioxidant levels in smokers, increased reactive advanced glycation end products, and direct toxicity from heavy metals found in cigarette smoke,” Dr. Varma says.

► Myopic refractive error, systolic blood pressure, female gender and large drusen. Research has not consistently confirmed the likely explanations for these independent risk factors, Dr. Varma says. “This is speculative, but my sense is that the location of opacities has to do with the impact of all risk factors,” he says. “We will know more as research continues.”

Vegetarian Benefit?

A recent study out of the United Kingdom investigated the association between diet and cataract risk in a population with varied diets, including many vegetarians.⁹ The study involved 27,670 self-reported nondiabetic participants age 40 and older at recruitment, and found vegetarians in the cohort to be at lower risk of cataract than meat eaters.

After multivariable adjustment, incidence rate ratios for high-meat eaters were considerably higher than those for moderate and low meat eaters, fish eaters, vegetarians and vegans. Co-authors Paul Appleby, Naomi Allen and Timothy Key have said their epidemiological study cannot be used as the basis of practical advice for patients.

“However, we would express the hope that ophthalmologists are aware of our study and others that have shown various measures of a healthy diet, such as the US Dietary Guidelines Healthy Eating Index, to be associated with a reduced risk of nuclear cataract or nuclear opacity,”^10,11 the investigators said. “There are many good reasons to follow a healthy diet and several studies suggest that lowering your risk of cataract can now be added to these. How far individuals move along the path toward a plant-based diet is a matter of personal choice.”

Controversy Over Carbs

A 2010 study found of 2,594 participants by Tufts researchers found a correlation between high carbohydrate intake and cortical cataract. The highest quartiles of carbohydrate intake corresponded with more than a twofold risk of developing cortical cataract.¹²

However, Italian researchers have challenged the perception that a higher carbohydrate intake is responsible for cataract development. “Although experimental evidence has suggested an association between nutrition and lens opacities, a defined role for dietary differences and cataract formation has not yet been ascertained,” they argued in a dissenting letter in Investigative Ophthalmology and Visual Science.¹³

The Italian researchers cited two older studies that showed a dietary deficiency of antioxidants development, and noted that studies of subjects in industrialized countries “failed to demonstrate significant differences in the blood levels of nutrients or metabolites between cataractous and controls subjects.”

The Italian investigators further contended the Tufts study failed to adequately consider patients with pre-diabetes by excluding only patients with diabetes (4.66% of the study population), noting that prediabetes can affect more than 15% of the population.

“In conclusion, we believe that carbohydrate intake, per se, is not responsible for cataract development in normal individuals,” the Italian investigators wrote. Instead, they added, the association should be made between carbohydrate intake and prediabetes.

Casting Doubt on Vitamin Therapy

Many ophthalmologists believe that continuing research will support the use of vitamins to minimize risk factors for cataract. But findings from one recent comprehensive study cast doubt on that. Investigators at MetroWest Medical Center in Framington, Mass., evaluated 117,272 individuals from nine trials to assess the effectiveness of antioxidant vitamin supplementation in preventing and slowing cataract progression.¹⁴

“There is no evidence from random controlled trials that supplementation with antioxidant vitamins (beta-carotene, vitamin C or vitamin E) prevents or slows the progression of age-related cataract,” the investigators concluded. “We do not recommend any further studies to examine the role of antioxidant vitamins beta-carotene, vitamin C and vitamin E in preventing or slowing the progression of age-related cataract. Costs and adverse effects should be weighed carefully with unproven benefits before recommending their intake above recommended daily allowances.”

Meanwhile, another trial found long-term alternate-day use of 400 IU of vitamin E and daily use of 500 mg of vitamin C had no notable beneficial or harmful effect on the risk of cataract.¹⁵ The randomized, double-masked, placebo-controlled trial involved 11,545 apparently healthy male physicians, age 50 or older, in the United States who had no diagnosis of cataract at baseline.

“I still believe a good balance of vitamins and good nutrition makes a difference,” says Robert Abel, Jr., MD., of Delaware Opthalmology Consultants in Wilmington. Dr. Abel is an advocate of alternative treatments and has created his own formulation of vitamins for preventive care. “The key is not to get lost in the arguments of specific studies. If you look at the balance of literature, you can see that there appear to be ways to protect the crystalline lens through a healthy lifestyle and diet,” he says. “We can debate the merits of specific approaches but I believe we serve our patients’ best interest by advocating for all possible options that pose no harm and seem to offer the best long-term benefit.” OM

A Three-month Wait For Ophthalmic Nutrition Counseling

Jeffrey Morris, MD, MPH, director of the Morris Eye Group, Encinitas and Vista, Calif., is building a unique profit center around a new non-mydriatic, non-invasive densometer called the MAPCATsf (Guardion Health Sciences). This instrument tracks and quantifies macular pigment optical density (MPOD). Dr. Morris has hired a nutritionist who administers the test, provides nutritional counseling and, if indicated, recommends changes in diet and appropriate vitamin supplements. “Our patients have enthusiastically accepted this service because they really enjoy having a professional help them navigate the vitamin and supplement market, using sciencebased advice,” Dr. Morris says. MAPCATsf measures macular pigment optical density. The new nutritional service attracts 12 new patients a day and has already developed a three-month backlog. Most of the patients come from his existing practice. “Once the patient adopts behavior modification changes and dietary changes in consultation with the nutritionist, we see up to a 35% improvement in MPOD within three months,” he notes. Data for Nutritionist Besides MPOD, the desktop MAPCATsf measures lens optical density, the effective age of the lens and the percentage of short-wavelength blue light that MPOD blocks. The nutritionist uses this data to establish baseline measurements and subsequently track visual performance with contrast sensitivity and glare testing. One report noted the test continues to become more relevant to anterior segment specialists. Updated data from the Beaver Dam Eye Study demonstrated that cataract patients may increase their risk for AMD by undergoing cataract surgery.1 “Using nutritional support to fortify the vulnerable central retina is essential for all patients at risk for agerelated eye disease,” Dr. Morris advises. Previous research has confirmed the central retina requires an abundant supply of meso-zeaxanthin, a stereoisomer of zeaxanthin generally not available in food but converted from lutein. The macula also requires rich amounts of lutein and zeaxanthin — provided only through diet and nutritional supplements — to filter out damaging blue light. A Three-month Wait Lutein and Zeaxanthin Observational studies dating back to the 1990s have established an association between lutein and zeaxanthin dietary intake and reduced risk for AMD. More recent research has correlated high levels of MPOD with improved visual performance.2 The average daily Western diet includes insufficient levels of lutein and zeaxanthin. A daily combined dose of 27 mg of lutein, zeaxanthin and meso-zeaxanthin, the stereoisomer not generally available in food, is available in Lumega-Z, a daily singledose, vacuum-packaged liquid supplement (Guardion Health Sciences). According to Dr. Morris, the treatment can effectively repigment the macula, enhancing visual protection and visual performance. References 1. Klein BEK, Howard KP, LeeKE, et al. The relationship of cataract and cataract extraction to age-related macular degeneration: the Beaver Dam Eye Study. Ophthalmology. 2012;119:1628-1633. 2. Loughman J, Nolan JM, Howard AN, et al. The impact of macular pigment augmentation on visual performance using different carotenoid formulations. Invest Ophthalmol Vis Sci. 2012;53:7871-7880.

References

1. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001;119:1417-143 6.

2. Age-Related Eye Disease Study 2: The Lutein/Zeaxanthin and Omega-3 Supplementation Trial. Available at www.areds2.org. Accessed December 11, 2012.

3. Richter GM, Torres M, Choudhury F, Azen SP, Varma R. Risk factors for cortical, nuclear, posterior subcapsular, and mixed lens opacities: the Los Angeles Latino Eye Study. Ophthalmology. 2012;119:547-554.

4. AREDS Research Group. Associations of mortality with ocular disorders and an intervention of highdose antioxidants and zinc in the Age-Related Eye Disease Study: AREDS report no. 13. Arch Ophthalmol. 2004;122:716-726.

5. McCarty CA, Taylor HR. A review of the epidemiologic evidence linking ultraviolet radiation and cataracts. Dev Ophthalmol. 2002;35:21-31.

6. Leske MC, Wu SY, Nemesure B, Hennis A, Barbados Eye Studies Group. Risk factors for incident nuclear opacities. Ophthalmology. 2002;109:1303-1308.

7. Klein BE, Klein R, Wang Q, Moss SE. Older-onset diabetes and lens opacities: the Beaver Dam Eye Study. Ophthalmic Epidemiol. 1995;2:49-55.

8. Delcourt C, Cristol JP, Tessier F, et al, POLA Study Group. Risk factors for cortical, nuclear, and posterior sub-capsular cataracts: the POLA study. Am J Epidemiol. 2000;151:497-504.

9. Appleby PN, Allen NE, Key TJ. Diet, vegetarianism, and cataract risk. Am J Clin Nutr. 2011;93:1128-1135.

10.Mares JA, Voland R, Adler R, et al. Healthy diets and the subsequent prevalence of nuclear cataract in women. Arch Ophthalmol. 2010;128:738-749.

11.Moeller SM, Taylor A, Tucker KL, et al. Overall adherence to the dietary guidelines for Americans is associated with reduced prevalence of early age-related nuclear lens opacities in women. J Nutr. 2004;134:1812-1819.

12. Chiu CJ, Robman L, McCarty CA, et al. Dietary carbohydrate in relation to cortical and nuclear lens opacities in the Melbourne visual impairment project. Invest Ophthalmol Vis Sci. 2010;51:2897-2905.

13.Costagliola C, Lobefalo L, Gallenga PE. Role of higher dietary carbohydrate intake in cataract development. IOVS. 2011;52:3593.

14.Mathew MC, Ervin AM, Tao J, Davis RM. Antioxidant vitamin supplementation for preventing and slowing the progression of age-related cataract. Cochrane Database Syst Rev. 2012 Jun 13;6:CD004567.

15. Christen WG, Glynn RJ, Sesso HD, et al. Age-related cataract in a randomized trial of vitamins E and C in men. Arch Ophthalmol. 2010;128:1397-1405.