November 2010




The not-so-sweet truth about cataracts

by Maxine Lipner Senior EyeWorld Contributing Editor


Dietary risk factor for cortical cataracts: making a carbohydrate connection

Cortical cataract formation can be spurred by excessive carbohydrate consumption Source: Chung-Jung Chiu, D.D.S., Ph.D.

Excessive carbohydrate intake may lead to increased cataract risk, according to Chung-Jung Chiu, D.D.S., Ph.D., assistant professor, School of Medicine, Tufts University, Boston. Recent results published in the June issue of Investigative Ophthalmology and Visual Science showed that pure cortical cataracts are associated with total carbohydrate intake.

Investigators were spurred to consider a potential carbohydrate connection to cataract by previous work. "Carbohydrate is the most important energy source in the human body," Dr. Chiu said. "Considerable evidence has linked aberrant glucose metabolism or diabetes to cataract risk, and in vitro and in vivo animal studies also suggest that carbohydrates play an important role in cataractogenesis."

Included in the study were patients from the Melbourne Visual Impairment Project. "The Melbourne Visual Impairment Project is a population-based, prospective study established to address the clinical course, prognosis, risk factors, and prevention strategy for eye disease," Dr. Chiu said. "Eligible participants were recruited via a household census from the permanent residents in nine pairs of census collector districts randomly selected from the Melbourne statistical division."

The Melbourne Visual Impairment Project included a total of 3,271 participants who were all over age 40 at baseline recruitment and took place from 1992 to 1994. Investigators gathered data on possible risk factors for cataract from a baseline general physical exam together with ophthalmic photography and a detailed questionnaire on basic characteristics and demographic data at the time of the household census. Five years later, all participants were traced and those still living in the selected areas were invited to return to locally established test sites for a follow-up examination. "The follow-up examinations were attended by 2,594 participants and involved the same protocol as was used at baseline," Dr. Chiu said. "In addition, a validated food frequency questionnaire was administered."

Studying dietary carbohydrates

From this broad epidemiologic trial, investigators led by Dr. Chiu selected 197 eyes with pure cortical cataract, 366 eyes with pure nuclear cataract, and 2,385 eyes without any type of cataract to study further. They considered dietary information from a semi-quantitative food frequency questionnaire. When they analyzed the data, they found that there appeared to be a connection between cortical cataract development and carbohydrate consumption. "Results from the present analysis are consistent with the epidemiologic data showing that there is a positive relation between total carbohydrate intake and risk of cortical cataract," Dr. Chiu said.

He theorizes that in an environment of excessive glucose, lens proteins are modified, spurring cataract formation. "Prolonged exposure of lens proteins to excess glucose results in extensive glycation," he said. "The consequences of this may include oxidation, cross-linking, aggregation, and precipitation of the modified lens proteins, leading to a cataract."

It is no surprise that it was cortical cataracts in particular that were linked to carbohydrate consumption. "Nuclear magnetic resonance studies indicate that glucose concentrations remain higher in the cortex than in the nucleus," Dr. Chiu said. "So it would appear that higher carbohydrate intake and plasma concentrations of glucose will result in chronically enhanced exposure of lens cortex proteins to glucose."

Dr. Chiu points out that in addition, enzyme activities involved in the metabolism of glucose decrease toward the center of the lens. "This is consistent with higher concentrations of glucose and glucose transporters in the cortex than in the lens nucleus," he said. "These effects may result in enhanced cortical protein modification, precipitation, and (then) cataract because the lens proteins are extremely long-lived, having half-lives of decades." In addition, opportunities for repair or removal and replacement of these damaged proteins are limited. Information gleaned from the study mirrors that found in diabetic cataract investigations. "The data are consistent with in vivo evidence that the precipitation of glycated lens proteins in diabetic cataractogenesis is initiated in the cortical region," Dr. Chiu said. "It is interesting that epidemiologic studies also show that carbohydrate metabolism and diabetes have more consistently been linked with cortical cataract than with nuclear opacities."

Modifiable risk factor

Dr. Chiu hopes that practitioners will come away from the study with deeper insights into the dietary cataract connection. "Dietary carbohydrate intake is a modifiable risk factor for the prevention of cataract," he said. "In addition to other risk factors for cataract such as smoking, ophthalmic clinicians should consider that dietary carbohydrate may account for some risk of cataract."

Overall, Dr. Chiu thinks that the ocular effects of carbohydrates are likely not limited to cataracts and may be important for ophthalmologists to keep in mind for numerous conditions. "Our recent studies also showed that dietary carbohydrate is a modifiable risk factor for age-related macular degeneration," he said. "It may be true that dietary carbohydrates have effects on eye health in general."

Editors' note: Dr. Chiu has no financial interests related to his comments.

Contact information

Chiu: 617-556-3157,

The not-so-sweet truth about cataracts The not-so-sweet truth about cataracts
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