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Association Between Breastfeeding and Likelihood of Myopia in Children
To the Editor: Nearsightedness is the leading cause of visual impairment in developed countries, present in 30.4 million adults in the United States alone.1 The increasing prevalence of myopia, especially among urban Asian children,2 suggests that early lifestyle factors may play a role. Early visual experiences affect the growth of the eye,3 and nutritionally mediated deficiencies in retinal or visual development in infancy may predispose to myopia. We therefore studied the association of breastfeeding with myopia in Asian school children by using the population in the Singapore Cohort Study of the Risk Factors for Myopia.
Methods
The study population was taken from all children in grades 1 to 3 of a single junior school in Singapore in 2001, with an 80.2% participation rate. Children with congenital eye disorders were excluded. We conducted a cross-sectional analysis of this cohort in May 2004, when the participants were ages 10 to 12 years. Parents completed questionnaires 1 month before their children’s annual eye examinations. The parents were asked if their child had ever been breastfed and for what duration, and to describe breastfeeding as exclusive, mostly (nonformula supplements), or partly (formula supplements). Parents were not aware of the study hypothesis and breastfeeding questions were mixed with unrelated questions. Research assistants performing the eye examinations were masked to the results of the questionnaire. Parents were aware of their child’s myopia except for 56 children whose myopia was newly diagnosed after completing the questionnaire. We performed cycloplegic autorefraction with an autokeratorefractometer (Canon Inc Ltd, Tochigiken, Japan) and diagnosed myopia as spherical equivalent refraction of at least –0.5 diopters (D). We obtained institutional ethics board approval and parental written consent for all children.
Race/ethnicity was assessed by parental self-report and IQ score was measured by the Raven Standard Progressive Matrices Test.4 Proportions and means were compared using  2 tests and t tests, respectively; 2 tests for trend were used for proportions with more than 2 ordered levels. Multiple logistic regression and multiple linear regression models were constructed with myopia and refractive error as the dependent variables, respectively, adjusting for child’s age, sex, race, birth weight, height, books read per week, IQ scores,4 mother’s education,5 parental myopia, maternal age at delivery, and household income, and accounting for clustering of siblings within families. No interactions were found. Statistical significance was defined as P<.05. Statistical analysis was performed using SAS version 8.02 (SAS Institute Inc, Cary, NC) and Stata version 8.0 (StataCorp LP, College Station, Tex).
Results
Of the 961 children who enrolled in 2001, 797 (82.9%) were reexamined in May 2004. There was no significant difference between participants and nonparticipants with respect to sex, age, or race. Myopia was present in 521 children (65.4%; 95% confidence interval [CI], 62.0-68.7). A total of 418 (52.4%) of 797 children had been breastfed (68 [8.5%] exclusively, 62 [7.8%] mostly, and 288 [36.1%] partly). A total of 298 children (37.4%) were breastfed for 3 months or less; 120 [15.0%] were breastfed longer. The characteristics of children with and without myopia are shown in the Table.
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Table. Characteristics of Children With and Without Myopia*
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Children who were breastfed had lower myopia prevalence (259 [62.0%] of 418) than children who were not breastfed (262 [69.1%] of 379) (P = .04). A history of being breastfed was associated with decreased odds of myopia (odds ratio [OR], 0.73; 95% CI, 0.54-0.98) and remained decreased after adjustment (OR, 0.58; 95% CI, 0.39-0.84). The mean spherical equivalent refraction of breastfed children (–1.6 D) was less myopic than that of nonbreastfed children (–2.1 D) and remained significant after adjustment (P = .001). Duration of breastfeeding was not associated with myopia ( 3 months vs >3 months; OR, 0.87; 95% CI, 0.51-1.48). The type of breastfeeding (exclusive, mostly, or partly) was not significantly associated with myopia.
Comment
In this cross-sectional study, breastfeeding was independently associated with decreased likelihood of myopia after controlling for known risk factors. Breastfeeding has been linked with neurodevelopment, affecting visual acuity in young children.6 Until weaning occurs, breast milk is the main source of many micronutrients including docosahexaenoic acid, which is important for photoreceptor and cortical neuronal development.6
Certain limitations need to be considered in interpreting these results. Retrospective collection of breastfeeding data raises a possibility of recall bias, but this is unlikely since parents were unaware of the study hypothesis. As a cross-sectional study, the results indicate association, not causality. Uncontrolled confounding may have been present. Although statistically significant, the ORs have very wide CIs, with the upper end approaching 1. The incidence and progression rates of myopia in Singaporean children, like those of Taiwan and Hong Kong, are among the highest in the world,2 about double the rates in the United States,7 possibly limiting generalizability.
For these reasons, this study should be considered hypothesis-generating. We recommend prospective studies (cohort or randomized controlled trials) that quantify breastfeeding and evaluate the incidence of myopia in childhood. Confirmation of a protective effect would support the value of breastfeeding.
Access to Data: Dr Chong had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Financial Disclosures: None reported.
Funding/Support: This study was funded by grants NMRC/0695/2002 from the National Medical Research Council and EY-07354 from the National Institutes of Health, the Paul and Evanina Bell Mackall Foundation Trust, and Research to Prevent Blindness.
Role of the Sponsor: The study’s sponsors had no role in the design and conduct of the study, in the collection, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript.
Yap-Seng Chong, MD
obgcys{at}nus.edu.sg
Department of Obstetrics and Gynaecology
National University of Singapore
National University Hospital
Singapore
Yu Liang, MSc;
Donald Tan, FRCOphth
Singapore Eye Research Institute
Singapore
Gus Gazzard, FRCOphth
Institute of Ophthalmology
London, England
Richard A. Stone, MD
Department of Ophthalmology
Scheie Eye Institute
University of Pennsylvania School of Medicine
Philadelphia
Seang-Mei Saw, PhD
Department of Community, Occupational, and Family Medicine
National University of Singapore
Singapore
1. Congdon NG, Friedman DS, Lietman T. Important causes of visual impairment in the world today. JAMA. 2003;290:2057-2060.
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2. Saw SM, Tong L, Chua WH, et al. Incidence and progression of myopia in Singaporean school children. Invest Ophthalmol Vis Sci. 2005;46:51-57.
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3. Quinn GE, Shin CH, Maguire MG, Stone RA. Myopia and ambient lighting at night. Nature. 1999;399:113-114.
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4. Saw SM, Tan SB, Fung D, et al. IQ and the association with myopia in children. Invest Ophthalmol Vis Sci. 2004;45:2943-2948.
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5. Winkleby MA, Kraemer HC, Ahn DK, Varady AN. Ethnic and socioeconomic differences in cardiovascular disease risk factors: findings for women from the Third National Health and Nutrition Examination Survey, 1988-1994. JAMA. 1998;280:356-362.
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6. Williams C, Birch EE, Emmett PM, Northstone K, Avon Longitudinal Study of Pregnancy and Childhood Study Team. Stereoacuity at age 3.5 y in children born full-term is associated with prenatal and postnatal dietary factors: a report from a population-based cohort study. Am J Clin Nutr. 2001;73:316-322.
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7. Kleinstein RN, Jones LA, Hullett S, et al. Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study Group: refractive error and ethnicity in children. Arch Ophthalmol. 2003;121:1141-1147.
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Letters Section Editor: Robert M. Golub, MD, Senior Editor
JAMA. 2005;293:3001-3002.
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