- Email: [email protected]
Breastfeeding, atopy, and asthma
CORRESPONDENCE
COMMENTARY
CORRESPONDENCE e-mail submissions to [email protected]
Breastfeeding, atopy, and asthma Sir—Malcolm Sears and colleagues (Sept 21, p 901)1 conclude that breastfeeding could have a role in the development of atopy and asthma. We believe that such a message could have a potential negative public health effect on infant feeding practices, and is not supported by their findings. Such a strong conclusion would require a precise, prospective, and frequent documentation of breastfeeding practices.2 However, in the study, all information on infant feeding during the first 36 months was documented retrospectively by interviewing mothers when the child was 3 years old. A retrospective assessment can yield information biases with regard to exact breastfeeding methods (ie, exclusive, predominant, or mixed) and duration of breastfeeding.2 According to WHO definitions,3 most of the breastfed children included in this study would be neither exclusively, nor predominantly, but mixed breastfed. Thus, the higher risk of atopy and asthma reported in breastfed children might be due to the introduction of complementary foods in mixed breastfed children rather than to breastmilk. In that case, these results would not contradict those of Oddy and colleagues,4 who showed a protective effect of exclusive breastfeeding against asthma and atopy. Consequently, we strongly feel that, instead of pooling non-breastfed children and children breastfed for less than 4 weeks, the authors should have compared children exposed to breastmilk, whatever the duration, with children who were never breastfed. Additionally, further stratified analyses or studies are required to explore the proper effects of exclusive, predominant, and mixed breastfeeding in the development of atopy and asthma. Finally, to suggest that the increase in atopy and asthma in the past three decades would be explained by the increasing prevalence of breastfeeding is confusing. Indeed, because the role of many environmental factors is dominant in the development of asthma,5 their evolution has to be taken into account before reaching that conclusion.
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Meanwhile, we believe that this study does not provide any convincing evidence leading to reconsideration of the promotion of breastfeeding in developed countries. *Renaud Becquet, Valériane Leroy, L Rachid Salmi Unité INSERM 330, Université Victor Segalen Bordeaux 2, 33076 Bordeaux Cedex, France (e-mail: [email protected]) 1
2
3
4
5
Sears MR, Greene JM, Willan AR, et al. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study. Lancet 2002; 360: 901–07. Piwoz EG, Creed de Kanashiro H, Lopez de Romana G, Black RE, Brown KH. Potential for misclassification of infants’ usual feeding practices using 24-hour dietary assessment methods. J Nutr 1995; 125: 57–65. World Health Organization. Indicators for assessing breast-feeding practices: report of an informal meeting. Geneva: World Health Organization, 1991: 14. Oddy WH, Holt PG, Sly PD, et al. Association between breast feeding and asthma in 6 year old children: findings of a prospective birth cohort study. BMJ 1999; 319: 815–19. Sears MR. Epidemiology of childhood asthma. Lancet 1997; 350: 1015–20.
Sir—Malcolm Sears and colleagues1 state that breastfed infants’ exposure to cows’ milk formula in the maternity hospital did not bias their findings of an association between atopy and breastfeeding. I disagree. Exclusive breastfeeding has been shown to have benefits above and beyond those of partial breastfeeding. For example, partial breastfeeding results in increased vertical transmission of HIV from infected mothers compared with exclusive breastfeeding.2 Sears and colleagues did not allow for possible differing results between those who were truly exclusively breastfed and those who were not. This raises the issue of definition. The accepted WHO/UNICEF definition of an exclusively breastfed infant is one who has: “received only milk from a mother or wet nurse, or expressed breastmilk, and no other liquids or solids with the exception of drops or syrups consisting of vitamins, mineral supplements, or medicines”.
The authors cite Kramer’s study,3 and use it to justify their methods. However, one of Kramer’s requirements was for sufficient duration and exclusivity of breastfeeding, a condition which was not met in this study. Consequently, this article adds nothing to current knowledge of the relation between breastfeeding and asthma. Despite the detail of the follow-up investigations on the development of atopy, lack of suitable control groups makes the results irrelevant. Sears and colleagues conclude their article by speculating that “some of the increase in atopy and asthma in the past three decades. . . could be associated with. . . the prevalence of breastfeeding”. Presumably, then, in the era before the advent of formula feeding, when breastfeeding was the norm, there were high rates of asthma which subsequently dropped with widespread use of formula? In conclusion, there is simply not enough evidence to support this claim. A large-scale study conforming to Kramer’s criteria has yet to be done. Eithne Murray National Childbirth Trust, Alexandra House, Oldham Terrace, London W3 6NH, UK (e-mail: [email protected]) 1
Sears MR, Greene JM, Willan AR, et al. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study. Lancet 2002; 360: 901–07. 2 Coutsoudis A. Influence of infant feeding patterns on early mother-to-child transmission of HIV-1 in Durban, South Africa. Ann N Y Acad Sci 2000; 918: 136–44. 3 Kramer MS. Does breastfeeding help protect against atopic disease? Biology, methodology and a golden jubilee of controversy. J Pediatr 1988; 112: 181–90.
Sir—Malcolm Sears and colleagues1 report that breastfeeding does not protect children against atopy and asthma, and that breastfed children might even have an increased risk. As mentioned by Sears and colleagues, the hygiene hypothesis is now widely accepted as an explanation for the increased incidence of allergy in recent years. Several studies have shown that high exposure to antigens or allergens is associated with a decreased incidence of allergy and autoimmune
THE LANCET • Vol 361 • January 11, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet Publishing Group.
COMMENTARY
CORRESPONDENCE e-mail submissions to [email protected]
Breastfeeding, atopy, and asthma Sir—Malcolm Sears and colleagues (Sept 21, p 901)1 conclude that breastfeeding could have a role in the development of atopy and asthma. We believe that such a message could have a potential negative public health effect on infant feeding practices, and is not supported by their findings. Such a strong conclusion would require a precise, prospective, and frequent documentation of breastfeeding practices.2 However, in the study, all information on infant feeding during the first 36 months was documented retrospectively by interviewing mothers when the child was 3 years old. A retrospective assessment can yield information biases with regard to exact breastfeeding methods (ie, exclusive, predominant, or mixed) and duration of breastfeeding.2 According to WHO definitions,3 most of the breastfed children included in this study would be neither exclusively, nor predominantly, but mixed breastfed. Thus, the higher risk of atopy and asthma reported in breastfed children might be due to the introduction of complementary foods in mixed breastfed children rather than to breastmilk. In that case, these results would not contradict those of Oddy and colleagues,4 who showed a protective effect of exclusive breastfeeding against asthma and atopy. Consequently, we strongly feel that, instead of pooling non-breastfed children and children breastfed for less than 4 weeks, the authors should have compared children exposed to breastmilk, whatever the duration, with children who were never breastfed. Additionally, further stratified analyses or studies are required to explore the proper effects of exclusive, predominant, and mixed breastfeeding in the development of atopy and asthma. Finally, to suggest that the increase in atopy and asthma in the past three decades would be explained by the increasing prevalence of breastfeeding is confusing. Indeed, because the role of many environmental factors is dominant in the development of asthma,5 their evolution has to be taken into account before reaching that conclusion.
174
Meanwhile, we believe that this study does not provide any convincing evidence leading to reconsideration of the promotion of breastfeeding in developed countries. *Renaud Becquet, Valériane Leroy, L Rachid Salmi Unité INSERM 330, Université Victor Segalen Bordeaux 2, 33076 Bordeaux Cedex, France (e-mail: [email protected]) 1
2
3
4
5
Sears MR, Greene JM, Willan AR, et al. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study. Lancet 2002; 360: 901–07. Piwoz EG, Creed de Kanashiro H, Lopez de Romana G, Black RE, Brown KH. Potential for misclassification of infants’ usual feeding practices using 24-hour dietary assessment methods. J Nutr 1995; 125: 57–65. World Health Organization. Indicators for assessing breast-feeding practices: report of an informal meeting. Geneva: World Health Organization, 1991: 14. Oddy WH, Holt PG, Sly PD, et al. Association between breast feeding and asthma in 6 year old children: findings of a prospective birth cohort study. BMJ 1999; 319: 815–19. Sears MR. Epidemiology of childhood asthma. Lancet 1997; 350: 1015–20.
Sir—Malcolm Sears and colleagues1 state that breastfed infants’ exposure to cows’ milk formula in the maternity hospital did not bias their findings of an association between atopy and breastfeeding. I disagree. Exclusive breastfeeding has been shown to have benefits above and beyond those of partial breastfeeding. For example, partial breastfeeding results in increased vertical transmission of HIV from infected mothers compared with exclusive breastfeeding.2 Sears and colleagues did not allow for possible differing results between those who were truly exclusively breastfed and those who were not. This raises the issue of definition. The accepted WHO/UNICEF definition of an exclusively breastfed infant is one who has: “received only milk from a mother or wet nurse, or expressed breastmilk, and no other liquids or solids with the exception of drops or syrups consisting of vitamins, mineral supplements, or medicines”.
The authors cite Kramer’s study,3 and use it to justify their methods. However, one of Kramer’s requirements was for sufficient duration and exclusivity of breastfeeding, a condition which was not met in this study. Consequently, this article adds nothing to current knowledge of the relation between breastfeeding and asthma. Despite the detail of the follow-up investigations on the development of atopy, lack of suitable control groups makes the results irrelevant. Sears and colleagues conclude their article by speculating that “some of the increase in atopy and asthma in the past three decades. . . could be associated with. . . the prevalence of breastfeeding”. Presumably, then, in the era before the advent of formula feeding, when breastfeeding was the norm, there were high rates of asthma which subsequently dropped with widespread use of formula? In conclusion, there is simply not enough evidence to support this claim. A large-scale study conforming to Kramer’s criteria has yet to be done. Eithne Murray National Childbirth Trust, Alexandra House, Oldham Terrace, London W3 6NH, UK (e-mail: [email protected]) 1
Sears MR, Greene JM, Willan AR, et al. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study. Lancet 2002; 360: 901–07. 2 Coutsoudis A. Influence of infant feeding patterns on early mother-to-child transmission of HIV-1 in Durban, South Africa. Ann N Y Acad Sci 2000; 918: 136–44. 3 Kramer MS. Does breastfeeding help protect against atopic disease? Biology, methodology and a golden jubilee of controversy. J Pediatr 1988; 112: 181–90.
Sir—Malcolm Sears and colleagues1 report that breastfeeding does not protect children against atopy and asthma, and that breastfed children might even have an increased risk. As mentioned by Sears and colleagues, the hygiene hypothesis is now widely accepted as an explanation for the increased incidence of allergy in recent years. Several studies have shown that high exposure to antigens or allergens is associated with a decreased incidence of allergy and autoimmune
THE LANCET • Vol 361 • January 11, 2003 • www.thelancet.com
For personal use. Only reproduce with permission from The Lancet Publishing Group.