The Lack of Association of Breastfeeding and Myopia in Children and Adolescents: Finding from a School-Based Study and a Meta-Analysis of the Literature

Methodological quality of the review: Low confidence

Author: Rong-Kun Wu, Jing-Hong Liang, Hua Zhong, Jun Li, and Chen-Wei Pan

Region: Not reported

Sector: Myopia

Subsector: Breastfeeding and myopia

Equity focus: No

Study population: Children and adolescents

Type of programme: School based

Review type: Other review

Quantitative synthesis method: School-based study and a meta-analysis of the literature

Qualitative synthesis method: Not applicable

Background: Myopia is a significant global health concern, particularly in East Asians. The high prevalence of myopia poses a huge socioeconomic burden. Identifying risk factors is crucial for the prevention of early onset myopia. Breast milk is an infant’s first food and a substantial early life exposure, which is supposed to reduce the risk of myopia. In addition, insulin-like growth factor-I (IGF-I) in breast milk promotes normal vascularisation of the retina. Some studies found a protective effect of breastfeeding on myopia, whereas others reported non-significant findings. A comprehensive understanding of the relationship between breastfeeding and myopia may provide novel insights into the effective prevention strategy of myopia at an early stage of life.

Objectives: The objective of this review was to confirm the relationship between breastfeeding and myopia from available observational studies.

Main findings: A total of eight studies (four cross-sectional studies and one birth cohort study), which provided effect estimates on the association between breastfeeding and myopia, were finally considered eligible for inclusion in the meta-analysis. All of those studies included 29,849 individuals, among whom 14,182 (47.51%) had never been breastfed. Prevalence of breastfeeding in these studies ranged from 22.00% to 91.22%. Prevalence of myopia in these studies ranged from 4.26% to 65.37%. Random-effects meta-analysis yielded a pooled OR showing no association between breastfeeding and myopia (OR: 0.93, 95% CI: 0.78-1.10, I²=60.8%, pheterogeneity (P)=0.01).

Based on findings, authors conclude that evidence did not support that breastfeeding could reduce the risk of myopia in children and adolescents.

Methodology: Inclusion criteria consisted of: 1) infants who had been breastfed compared with those who had never been breastfed; 2) the outcome was the presence of myopia in children aged 0 to 18 years; and 3) estimates of the association of having been breastfed with myopia were available in the published articles or could be derived. In addition, studies had been published in peer-reviewed journals in English. Myopia considered in the article did not involve treatment or therapeutic intervention. The meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A literature search was conducted to identify original studies assessing the association between breastfeeding and myopia among children and adolescents aged up to 18 years old. PubMed, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL) were used to search and identify relevant studies from their inception to 9 March 2019. Quality of the included studies was assessed using the Agency for Healthcare Research and Quality, a tool developed to assess quality of studies for meta-analyses. Based on the pre-customised criteria of inclusion and exclusion, the following information was independently extracted from each article using a purpose-built data collection Excel form: study characteristics (last name of the first author, year of publication, and study location); characteristics of targeted individuals (number of participants, participant rates, and age range); and study methodology (definition of breastfeeding and myopia). To evaluate the effect of breastfeeding on myopia, we calculated the ORs and 95% CIs from reported prevalence rates of myopia in different breastfeeding groups. Following results were revealed by forest plot that represented the effect of breastfeeding on myopia. Heterogeneity among studies was estimated using Cochran’s Q test (significance level at P<0.05) and I² The meta-analysis was performed using the Stata version 12.

Applicability/external validity: The authors acknowledged some limitations which need to be considered when interpreting the results: first, most included studies in this analysis were performed in East Asia, which features a high prevalence of myopia. Lack of data from Western countries may result in the absence of associations between breastfeeding and myopia in developed countries. Second, overall findings were based on observational epidemiologic studies, and they may lack sufficient power to determine any relationship. Third, breastfeeding data was based only on maternal recall, which may lead to recall bias.

Geographic focus: It is difficult to know if the review includes countries from LMIC, because the table summarising the included studies is not available.

Summary of quality assessment:

There is low confidence in this review’s findings, as important limitations were identified. Literature searches were not thorough enough to ensure that all relevant studies were identified and included in this review. In addition, methods used to extract data were not rigorous enough to ensure that biases were avoided.