JAMA Ophthalmology Journal Club Slides: Antioxidant Capacity of Diet and Risk of Cataracts

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JAMA Ophthalmology Journal Club Slides:Antioxidant Capacity of Diet and

Risk of Cataracts

Rautiainen S, Lindblad BE, Morgenstern R, Wolk A. Total antioxidant capacity of the diet and risk of age-related cataract: a population-based prospective cohort of women. JAMA Ophthalmol. Published online December 26, 2013. doi:10.1001/jamaophthalmol.2013.6241.


Introduction

• The prevalence of cataract is the leading cause of blindness worldwide.

• Antioxidants have been hypothesized to prevent cataract by inhibiting oxidative damage of lens proteins and lipids in the epithelium of the lens. However, no previous study has investigated the association between all antioxidants present in the diet and age-related cataract.

• The total antioxidant capacity (TAC) concept aims to measure the capacity from all dietary antioxidants in a single estimate by taking into account synergistic effects between compounds.

• Objective:

– To prospectively study the association between all dietary antioxidants (by summarizing the TAC of foods) and the incidence of age-related cataract in middle-aged and elderly women.


• Study Design: Questionnaire-based nutrition survey within the prospective Swedish Mammography Cohort, which was followed up for an average of 7.7 years for age-related cataract incidence.

• Participants: 30 607 women (aged 49-83 years) who were free of cancer, cardiovascular disease, diabetes, and cataract diagnosis at baseline in 1997.

• Dietary TAC was assessed from a 96-item food frequency questionnaire completed at baseline.

• Information about lifestyle, clinical, and dietary factors was collected from questionnaires completed at baseline.

Methods


• Dietary TAC estimates were created by using a database of the most common foods in the United States, analyzed with the oxygen radical absorbance capacity (ORAC) assay.

• Dietary TAC was calculated by multiplying the average frequency of consumption of each food item by ORAC content (micromole Trolox equivalents [TEs]) of age-specific portion sizes.

• Dietary TAC estimates were adjusted for total energy intake with the residual method.

Methods


Methods

• Cataract diagnoses and extractions were ascertained by linkage to the National Outpatient and Inpatient Registers at the National Board of Health and Welfare and to the “Swedish National Day-Surgery Register” (International Classification of Diseases, Tenth Revision, code H25 and operation codes CJC, CJD, CJE, and CJG).

• Women were also matched against local cataract extraction registers at both public and private clinics in the study area.

• Cataracts considered congenital or secondary to ocular trauma, intraocular inflammation, or previous intraocular surgery were excluded.


Methods

• Women in the cohort were followed up from baseline (September 15, 1997) until the date of cataract diagnosis, cataract extraction, death, migration out of the study area, or the end of follow-up (December 31, 2005), whichever came first.

• Women were categorized into quintiles of the TAC of the diet (TE/day).

• Cox proportional hazards model was used to estimate relative risks as rate ratios (RRs), with 95% confidence intervals.

• All RRs were adjusted for potential risk factors, including age, smoking, waist circumference, educational level, hypertension, hormone replacement therapy, corticosteroids, dietary supplement use, alcohol consumption, and energy intake.


Methods

• Limitations

– We were not able to use standardized eye examination of all women in this large cohort, performed preferably by 1 ophthalmologist, and therefore cannot exclude the possibility of misclassification of the outcome.

– We cannot exclude that women with cataract diagnosis could be more health conscious and more likely to seek medical help for visual impairment. However, in the Swedish health care system, everyone has the same access with a patient charge of less than $50 per operation.

– We had no information on cataract subtype.

– Dietary TAC was measured using food frequency questionnaires; therefore, we cannot exclude some measurement error in the TAC of diet.


ResultsBaseline Characteristics of the Swedish Mammography Cohort (N=30,607)a

aValues are age standardized to the age distribution in the study population


RRs With 95% Confidence Intervals of Age-Related Cataract According to Quintiles of TAC of Diet

Results

P for trend = .03

0.93

1.000.99

0.87


Results

• We examined whether the association between the TAC of the diet and age-related cataract varied by potential risk factors related to oxidative stress such as age, smoking, waist circumference, and corticosteroid use.

• The inverse association was somewhat stronger among women aged 65 years or younger (P for interaction = .07) and corticosteroid users (P for interaction = .27). However, the test for interaction did attain statistical significance.

• The inverse association was similar across subgroups of smoking (P for interaction = .39) and waist circumference (P for interaction = .52).


• In this population-based prospective cohort study of middle-aged and elderly women, women in the highest quintile of TAC of the diet, as compared with the lowest quintile, had a 13% lower risk of incident age-related cataract.

• The association was consistent across subgroups defined by potential risk factors for age-related cataract and sources of oxidative stress.

• The major contributors to the TAC of the diet were fruits and vegetables (44.3%), whole grains (17.0%), and coffee (15.1%).

Comment


• To our knowledge, no previous study has examined the association between the TAC of the diet and the risk of age-related cataract.

• In the lens, high concentrations of dietary antioxidants such as lutein, zeaxanthin, vitamin C, and vitamin E are found; therefore, these compounds are hypothesized to be of major importance in preventing cataract development.

• Observational studies of these specific antioxidants from diet, supplements, and plasma concentrations as well as intervention trials have reported inconsistent results.

• In the diet, much wider ranges of antioxidants are present than those examined in the mentioned studies.

Comment


• If you have questions, please contact the corresponding author:

– Susanne Rautiainen, PhD, Institute of Environmental Medicine, Karolinska Institutet, Nobels väg 13, 171 77 Stockholm, Sweden ([email protected]).

Funding/Support

• This study was supported by the Swedish Research Council/Medicine and Swedish Council for Working Life and Social Research, Stockholm, Sweden.

Conflict of Interest Disclosures

• None reported.

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JAMA Ophthalmology Journal Club Slides: Antioxidant Capacity of Diet and Risk of Cataracts

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