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Fruit and vegetable intake and the risk of cataract in women^1,2,3

¹ From the Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital (WGC, SL, DAS, and JEB) and the Department of Ambulatory Care and Prevention (JEB), Harvard Medical School, Boston, MA, and the Department of Nutrition, the Harvard School of Public Health, Boston, MA (SL)

² Supported by research grants CA 47988, HL 43851, and EY 06633 from the National Institutes of Health.

³ Reprints not available. Address correspondence to WG Christen, 900 Commonwealth Avenue East, Boston, MA 02215-1204. E-mail: wchristen{at}rics.bwh.harvard.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION REFERENCES

 
BACKGROUND:: Prospective data on cataract in relation to total fruit and vegetable intake are limited.

OBJECTIVE:: We aimed to examine whether higher fruit and vegetable intake reduces the risk of cataract and cataract extraction in a large, prospective cohort of women.

DESIGN:: Fruit and vegetable intake was assessed at baseline in 1993 among 39 876 female health professionals with the use of a validated, semiquantitative food-frequency questionnaire. A total of 35 724 of these women were free of a diagnosis of cataract at baseline and were followed for incident cataract and cataract extraction. Cataract was defined as an incident, age-related lens opacity responsible for a reduction in best-corrected visual acuity to 20/30 or worse, based on self-report confirmed by medical record review. Individuals, rather than eyes, were the unit of analysis.

RESULTS:: During an average of 10 y of follow-up, 2067 cataracts and 1315 cataract extractions were confirmed. Compared with women in the lowest quintile of fruit and vegetable intake, women with higher intakes had modest 10–15% reduced risks of cataract (P for trend < 0.05). For cataract extraction, no significant inverse trend was observed (P for trend = 0.12).

CONCLUSION:: These prospective data suggest that high intake of fruit and vegetables may have a modest protective effect on cataract.

Key Words: Cataract • cataract extraction • fruit and vegetables • prospective cohort • Women's Health Study

	INTRODUCTION

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Basic science and animal research studies support a role for oxidative mechanisms in the etiology of cataract (1, 2). Thus, observational epidemiologic studies of dietary factors in cataract have focused on the amount of antioxidant nutrients contained in the diet. The most common approaches have been to examine the intake of specific nutrients or the serum concentrations of nutrients or biomarkers of fruit and vegetable intake. The results of these studies have been mixed. Whereas most studies report an inverse association between cataract and one or more antioxidant nutrients, the data for individual nutrients across studies have been inconsistent (2-4).

An alternative approach is to examine the development of cataract in relation to specific foods or food groups, such as total fruit and vegetable intake. This approach enables an assessment of the combined effects of antioxidant nutrients together with the effects of other components of the diet, such as other micronutrients, phytochemicals, and fiber. Several studies have examined the association of cataract with foods (5-13), but only one study used prospective data to examine cataract in relation to total fruit and vegetable intake (11).

We analyzed data from a large, prospective cohort of US female health professionals to assess the association of total fruit and vegetable intake with the risk of subsequent cataract. Because cigarette smoking is an established risk factor for cataract and an important source of oxidative stress (14-17), we also examined a priori whether the observed associations were modified by smoking status at baseline.

	SUBJECTS AND METHODS

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Subjects
The Women's Health Study (WHS) is an ongoing randomized, double-blind, placebo-controlled trial of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer among 39 876 apparently healthy female health professionals aged 45 y (18). Detailed information on fruit and vegetable intake was provided by 39 127 (98%) of the randomly assigned participants, who completed a 131-item validated semiquantitative food-frequency questionnaire (SFFQ) at baseline in 1993 (19). For this analysis we excluded participants who reported total energy intake<600 kcal/d or >3500 kcal/d, or who had >70 blanks on the SFFQ. Of the remainder, 35 724 participants had no diagnosis of cataract at baseline and were included. This study was conducted according to the ethical guidelines of Brigham and Women's Hospital.

Assessment of fruit and vegetable intake
All participants were requested to complete an SFFQ that included 29 vegetable items and 15 fruit items. For each fruit or vegetable, a standard unit or portion size was specified and participants were asked how often, on average, during the previous year they had consumed that amount. Nine responses were possible, which ranged from "never" to "6 times/d." Responses to the individual food items were converted to average daily intakes of each fruit and vegetable item for each subject, and the average daily intakes of individual fruit and vegetables were summed to compute total fruit and vegetable intake (19). In similar populations, the SFFQ was shown to have high validity as a measure of long-term average dietary intakes (20).

Other covariates
Information on possible risk factors for cataract was collected on the WHS baseline questionnaire. Information included age (in y), height and weight (expressed as body mass index; in kg/m²), smoking status (never, past, or current), alcohol use (rarely or never, 1–3 drinks/mo, 1–6 drinks/wk, or 1 drink/d), frequency of exercise (rarely or never, <1 times/wk, 1–3 times/wk, or 4 times/wk), parental history of myocardial infarction at age <60 y (no or yes), history of hypertension (no or yes), history of diabetes (no or yes), history of hypercholesterolemia (no or yes), menopause status (no or yes), postmenopausal hormone use (never, past, current), multivitamin use (no or yes), use of vitamin C supplements (no or yes), and history of an eye exam in the past 2 y (no or yes).

Ascertainment and definition of endpoints
Information on the occurrence of any relevant events, including cataract, was collected on annual questionnaires. After the report of a cataract diagnosis or extraction, the subjects were requested to provide written consent and to identify the treating ophthalmologist or optometrist. The ophthalmologists and optometrists were contacted by mail and requested to complete a cataract questionnaire to supply information about the presence of lens opacities, date of diagnosis, visual acuity loss, cataract extraction, other ocular abnormalities that could explain visual acuity loss, cataract type, and etiology (including age-related, traumatic, congenital, inflammatory, or surgery- or steroid-induced). As an alternative to completing the questionnaire, the ophthalmologists and optometrists were given the option of providing the relevant medical records. Medical record information was obtained for >91% of the participants who reported a cataract.

Endpoints were incident cataract and extraction of incident cataract. An incident cataract was defined as a self-report of a cataract that was confirmed by medical record review to have been first diagnosed after randomization, to be age-related in origin, and to be responsible for a decrease in best-corrected visual acuity to 20/30 or worse. In the presence of alternate ocular pathology, a lens opacity was considered a cataract if, in the judgment of the ophthalmologist or optometrist, the opacity was of sufficient severity to reduce visual acuity to 20/30 or worse when considered alone. Extraction was defined as the surgical removal of an incident cataract. Women who developed a non-age-related cataract or a cataract that did not reduce visual acuity to 20/30 or worse were included in the analyses as noncases.

Data analysis
Individuals, rather than eyes, were the unit of analysis because eyes were not examined independently, and participants were classified according to the status of the worse eye based on disease severity. Participants contributed person-years of follow-up until the time of diagnosis of cataract or censoring (death or February 2004, whichever came first). Fruit and vegetable intake was considered as a categorical variable (in quintiles), and we computed incidence rates of cataract by dividing the number of incident cases by person-years of follow-up in each quintile of fruit and vegetable intake. Estimates of relative risk (RR) were computed as the rate of cataract in a specific quintile of intake divided by the corresponding rate in the lowest quintile (reference). Crude RR estimates were obtained by adjusting for age (in y) and randomized treatment assignment in Cox proportional hazards regression models (21). Multivariate RRs were obtained by further adjusting for smoking, alcohol use, history of diabetes, history of hypertension, history of hypercholesterolemia, body mass index, physical activity, parental history of myocardial infarction, menopause status, postmenopausal hormone use, use of multivitamins or vitamin C supplements, total energy intake, and history of an eye exam in the past 2 y. For each RR, two-sided P values and 95% CIs were calculated (22). Tests of linear trend across increasing quintiles of fruit and vegetable intake were conducted by assigning the medians of intakes in quintiles (servings/d) treated as a continuous variable.

We also analyzed subgroup data according to baseline smoking status (current or noncurrent). Tests of interaction were performed to evaluate the statistical significance of any modifying effect of baseline smoking status on the association of fruit and vegetable intake with cataract. Data were analyzed with SAS (version 8; SAS Institute Inc, Cary, NC).

	RESULTS

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The reported mean (±SD) daily intake of fruit and vegetables at baseline was 6.0 ± 3.3 total servings, including 2.1 ± 1.4 servings of fruit and 3.9 ± 2.4 servings of vegetables. The median intake of fruit and vegetables ranged from 2.6 servings/d in the lowest quintile to 10 servings/d in the highest quintile. The distribution at baseline of possible risk factors for cataract according to quintiles of fruit and vegetable intake is shown in Table 1. Women with a high fruit and vegetable intake were older and were less likely to be current smokers. They also exercised more, had higher caloric intakes, and were more likely be postmenopausal, to use postmenopausal hormones, to use multivitamin supplements and supplements of vitamin C, and to report having had an eye exam in the past 2 y.

Table 2

Table 3

	DISCUSSION

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These prospective data, from female health professionals followed for an average of 10 y, indicated that >3.4 servings/d of fruit and vegetables is associated with modest 10–15% reduced risks of cataract and cataract extraction. The apparent modest relation did not change significantly after adjustment for smoking and other possible risk factors for cataract. Among the subgroup of women who were current smokers at baseline, the inverse association of cataract with fruit and vegetable intake appeared to be slightly stronger, although the interaction with smoking was not statistically significant when tested in multivariate models.

Several possible limitations of the study need to be considered. Misclassification of fruit and vegetable intake is always a major concern in any epidemiologic study of diet. In the WHS, information on fruit and vegetable intake was reported through a self-administered SFFQ collected at baseline. Because of the prospective design, however, measurement error in the assessment of fruit and vegetable intake was unlikely to be associated with the assessment of cataract endpoints. On the other hand, random or nondifferential misclassification, which would tend to underestimate any association of fruit and vegetable intake with risk of cataract, may have contributed to the weak associations observed. Changes in dietary practices during follow-up may have further contributed to the modest protective effect of fruit and vegetable intake observed in this study. Random misclassification of the cataract endpoint was reduced by the use of medical records to confirm the self-reports and by the use of strict diagnostic criteria that included a reduction in best-corrected visual acuity to 20/30 or worse because of cataract. Nonrandom or differential misclassification of cataract could occur if fruit and vegetable intake was associated with the frequency of medical contacts and, thus, with the likelihood of having an existing cataract diagnosed. In the WHS, women who reported a higher intake of fruit and vegetables were more likely to report having had an eye exam in the past 2 y. We included a term for the baseline report of an eye exam in the past 2 y in the multivariate analyses to control for possible surveillance bias. Finally, women with a higher intake of fruit and vegetables differed in several additional respects from those with a lower intake (Table 1). Although we did control for a number of measured confounders, other potential confounders that were either unmeasured or unknown may have contributed to the findings. Nonetheless, the relative homogeneity of the study population with respect to educational attainment and socioeconomic status should have minimized the possibility that other unknown confounding factors distorted the primary association between fruit and vegetable intake and risk of cataract.

To our knowledge, only 3 other studies examined the categories of all fruit and vegetable intake and the risk of cataract, and the results were inconclusive. One was a small, clinic-based, case-control study of 77 persons with cataract and 35 control subjects. In that study, those subjects with an average daily intake of fruit and vegetables above the 20th percentile (approximate cutoffs: 1.5 servings of fruit, 2 servings of vegetables, and 3.5 servings of fruit and vegetables) had a decreased risk of any type of cataract of 60%, compared with those below this frequency, after adjustment for age, sex, race, and diabetes (5). There was no information in that study on whether the risk of cataract continued to decrease with a higher frequency of fruit and vegetable intake. Cross-sectional data for 479 Nurse's Health Study participants aged 52–73 y (163 with a nuclear opacity in one or both eyes) indicated a moderately reduced odds of prevalent nuclear opacity for those reporting a high intake of fruit [odds ratio (OR) for the comparison of high (median: 3.9 servings) and low (median: 1.3 servings) quartiles: 0.58 (95% CI: 0.32,1.05); P for trend = 0.31] but not vegetables [OR for the comparison of high (median: 5.7 servings) and low (median: 2.4 servings) quartiles: 0.82 (95% CI, 0.47,1.42); P for trend = 0.99] in analyses adjusted for age, pack-years smoked, body mass index, vitamin C supplement use, and several other possible risk factors for cataract (13). In the Beaver Dam Eye Study, cross-sectional data for 1919 adults aged 43–84 y showed that a high intake of fruit and vegetables was associated with a reduced risk of prevalent nuclear sclerosis in men [OR for comparison of high (median: 4.9 servings) and low (median: 2.3 servings) quintiles: 0.68 (95% CI, 0.43,1.09); P for trend = 0.07] but not in women [OR for the comparison of high (median: 5.3 servings) and low (median: 2.9 servings) quintiles: 0.97 (95% CI: 0.65,1.46); P for trend = 0.90] in analyses adjusted for age, pack-years of smoking, and heavy alcohol use (7). Prospective data in that cohort, based on 5 y of follow-up during which 246 incident nuclear cataracts were identified, indicated no significant reduction in risk of cataract for those with high intake of vegetables (OR for the comparison of high and low quintiles: 0.7; 95% CI: 0.4, 1.2; P for trend = 0.39), and a possible elevated risk of cataract for those with high intake of fruit (OR: 1.8; 95% CI: 1.0, 3.3; P for trend = 0.07) after adjustment for age, energy intake, and pack-years of smoking (11). Separate results for men and women were not provided in that analysis. The results of our study, which is the largest to report on the category of all fruit and vegetable intake, suggest only a small overall benefit, if any, on cataract for women who consume >3.4 servings/d of fruit and vegetables.

We found no evidence to indicate that the association of fruit and vegetable intake with the risk of cataract was significantly modified by baseline smoking status. Cigarette smoking is an established risk factor for cataract (14-17), and available evidence supports a direct deleterious effect of smoking on the human lens (23-27). In addition, cigarette smoking is known to decrease plasma concentrations of ascorbate and, perhaps, lutein/zeaxanthin (28-32). Thus, cigarette smoking may indirectly aid cataract formation by lowering the plasma concentrations of nutrients that are important to the maintenance of lens transparency. Consumption of a diet rich in fruit and vegetables could, at least in theory, partially offset this effect of smoking on plasma nutrients. Results of other studies that examined antioxidant nutrients and cataract have not been consistent on this point: some suggest a stronger association in smokers (11, 33, 34) and others suggest a stronger association in nonsmokers (6, 9, 10).

In conclusion, these prospective data from a large cohort of well-nourished female health professionals indicate that a higher intake of fruit and vegetables was associated with only a slightly reduced risk of cataract. Additional observational studies in this and other cohorts and ongoing trials of dietary supplements may yet identify specific components of the diet that markedly reduce cataract formation. In the meantime, the possible beneficial effects of fruit and vegetables on the risk of many chronic diseases, including cataract, have a strong biological basis and warrant the continued recommendation to increase total intakes of fruit and vegetables.

	ACKNOWLEDGMENTS

 
We acknowledge the crucial contributions of the entire staff of the Women's Health Study, under the leadership of David Gordon, as well as Susan Burt, Mary Breen, Marilyn Chown, Lisa Fields-Johnson, Georgina Friedenberg, Inge Judge, Jean MacFadyen, Geneva McNair, David Potter, Claire Ridge, and Harriet Samuelson. We are also indebted to the dedicated participants of the Women's Health Study.

WGC participated in the data collection, data analysis, and writing of the first draft of the manuscript. JEB participated in the study design. JEB, SL, and DAS participated in the data analysis. All authors participated in the writing of the manuscript. None of the authors had any conflicts of interest.

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