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EDITORIAL |
1 From Pediatrics, Children's Nutrition Research Center, Baylor College of Medicine, Houston, TX
See corresponding article on page 1392.
Over the past several years, a number of randomized controlled trials have compared the effects of breastfeeding and formula feeding and the effects of docosahexaenoic acid (DHA)–supplemented and non-supplemented formulas on visual function in both preterm and term infants. Some studies have shown benefits of breastfeeding and of DHA-supplemented formulas, but others have not (1). Many studies have been criticized for the failure to control for a number of potentially important environmental and sociodemographic factors and for the failure to follow participants long enough to ascertain the persistence of any beneficial effects noted during the period of breastfeeding or DHA-supplemented formula feeding and, in some studies, up to 1 y or 18 mo later.
The study reported by Rudnicka et al (2), in this issue of the Journal, addresses some of these criticisms. These investigators report the prevalence of reduced vision, which they equate to myopia, at 10–11 and 15–16 y of age in 3 cohorts of British children born in 1946 (n = 5362), 1958 (n = 18 558), and 1970 (n = 16 567). The prevalence of reduced vision, defined as uncorrected distance vision of 20/40 or worse, ranged from 4.4 to 6.5% at 10–11 y of age and from 9.4% to 11.4% at 15–16 y of age.
Pooled odds ratios showed no association between feeding during infancy (breastfeeding compared with formula feeding) and vision at either age. However, there were associations between a number of other factors and reduced vision in both childhood and adolescence. These factors included higher parental education, higher maternal age, lower birth weight, fewer older siblings, and being female. Stronger associations with all of these factors, except the association with birth weight, were observed at 15–16 y of age than at 10–11 y of age. There also were significant associations between reduced vision in late childhood and adolescence and non-manual social class; however, as might have been expected, this as well as maternal age were highly correlated with parental education.
Although the study can be criticized on a number of grounds, it provides important insights about the association between infant feeding as well as a number of sociodemographic factors and vision at 10–11 and 15–16 y of age. Despite these potential shortcomings, it is clear that childhood vision remained relatively stable over a 24-y period during which breastfeeding declined from 65% in the 1946 cohort to 43% in the 1958 cohort to 22% in the 1970 cohort.
These findings in British children and adolescents differ from those of a similar but smaller study in Singaporean children (3). This study showed a lower likelihood of myopia in those who were breastfed (62% of 418 children compared with 69.1% of 379 children). Whether the 2 studies are comparable is not clear. Among other differences, the method of assessing vision appears to differ. In addition, the prevalence of myopia is much higher in Singaporean children, as is true also for children in Taiwan and Hong Kong. These vastly different prevalences of reduced vision limit the generalizability of both studies.
Rudnicka et al equated reduced vision to myopia, which is somewhat problematic. Although myopia is the most common cause of reduced vision in childhood, a number of children with hyperopia, astigmatism, and other problems are likely to have been included in the group with uncorrected distant vision. I do not see this as a major problem. The important finding is that lower vision at 10–12 and 15–16 y of age, for whatever reason, does not appear to be associated with whether the infant was breastfed or bottle-fed during infancy.
A more serious problem is that breastfeeding was defined simply as "yes" or "no," rather than as "exclusive," "mostly," or "partly." Furthermore, the duration of breastfeeding was not delineated, which is thought to be an important determinant of whether breastfeeding influences a variety of outcomes. Certainly, failure to include duration of breastfeeding will detract from the impact of the study.
As Rudnicka et al point out, failure to find an association with breastfeeding during early life and better vision at 10–11 and 15–16 y of age does not negate the many other advantages of breastfeeding. Thus, this study should not be interpreted as "anti-breastfeeding."
An important contribution of this study is the illustration of the impact of environmental and sociodemographic variables on visual outcome. This confirms the importance of controlling for these and perhaps other factors in studies of the effect of breastfeeding on vision and other outcomes.
ACKNOWLEDGMENTS
The author had no conflicts of interest to report.
REFERENCES
Related articles in AJCN:
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