Breastfeeding protects baby girls from serious chest infections but “does little to prevent respiratory illness in boys”, The Guardian reports. An Argentinean study found that “girls who received formula were eight times more likely to be hospitalised with respiratory illnesses”, the newspaper says.
The study examined a small group of premature, low birth weight infants and looked at the proportion requiring hospitalisation for bronchiolitis. This is a viral chest infection common in those aged less than a year, which causes cold symptoms, wheezing and breathing difficulties. The study has several limitations and further research is required to establish whether there is any gender difference in the protective effects of breastfeeding against chest infections. The benefits of breastfeeding for both mother and baby are well established and breastfeeding should continue to be promoted as the healthiest start in life for both girls and boys.
Where did the story come from?
This research was carried out by Dr M Inés Klein and colleagues at Fundación INFANT, Buenos Aires, and other institutes and organisations in Buenos Aires and Geneva; Johns Hopkins University, Baltimore, and National Institute of Health, North Carolina. The study was funded by a National Institute of Environmental Health Sciences contract mechanism with Johns Hopkins and Fundación INFANT, and the Director’s Challenge Award from the National Institute of Environmental Health Sciences. Two of the researchers in Argentina also received type I CONICET Doctoral Awards. It was published in the (peer-reviewed) medical journal Pediatrics .
What kind of scientific study was this?
This was a prospective cohort study designed to investigate whether the protective role of breastfeeding against severe lung disease differs according to gender in high-risk, newborn infants. The study was carried out between June 2003 and May 2005 at the Garrahan Children’s Hospital and Maternidad Sarda High Risk Clinics in Buenos Aires. The researchers followed 119 low birth weight, premature infants who had been recruited when they were discharged from the newborn intensive care unit. All infants’ corrected gestational age was less than six months and they had to weigh less than 1500g to be eligible for inclusion in the study. The study excluded infants with a life expectancy of less than six months, those with bleeding disorders, immune deficiency or orofacial abnormalities, or those who lived greater than 70km away from the study centre.
Parents were instructed on how to recognise respiratory symptoms and were asked to bring their baby to clinic whenever they developed any change from normal breathing patterns. All babies received monthly clinic monitoring and a doctor called the parents every fortnight to ask about respiratory symptoms. None of the babies received immunisation against respiratory syncytial virus – the common cause of bronchiolitis – because of cost constraints; the clinics predominantly monitor people of low socioeconomic status with a third of the patients being below the poverty line.
The researchers divided feeding patterns into exclusive breastfeeding or nonexclusive breastfeeding involving other supplementation. At each clinic visit, the duration of breastfeeding was established but the researchers were not able to assess the precise number of feeds given per day. Acute respiratory infection was defined as one or more symptoms of runny nose, sore throat, cough, wheezing, crackles on the chest (on stethoscope examination) or in-drawing of the chest muscles when breathing. Severe lung disease was defined as those requiring hospitalisation to maintain oxygenation. Changes in oxygen requirement and other respiratory status were assessed by paediatricians trained in the study protocol.
The researchers considered other variables that may affect susceptibility to infection (besides feeding pattern or gender), including birth weight, gestational age at birth, length of ventilatory support, length of stay in intensive care, number of smokers at home, other children at home, parental asthma, mother’s age and educational level, household income, and other features of the infective episode. Statistical analyses were carried to find out whether there was a difference between the rates of hospitalisation for boys and girls and how this was affected by breastfeeding, with adjustment for the above factors. They also looked at the difference between the average number of hospitalisations for boys and girls.
What were the results of the study?
Almost all infants were less than five months of corrected gestational age at the start of the study; 77% were aged less than three months and 34% less than one month of corrected age. Of the 119 infants, just over half were breastfeeding at the start of the study, but only four (one boy, three girls; 3%) were exclusively breastfeeding and receiving no other supplementation. There were no differences in overall breastfeeding rates or duration of breastfeeding between boys and girls. Eighty-eight infants (74%) had symptoms of chest infection during the study and 33 (28%) required hospitalisation for it. Forty-seven infants (40%) developed bronchopulmonary dysplasia (a chronic lung condition that premature babies are at risk of, where abnormally inflamed and scarred lung tissue develops). The average age at first episode of respiratory infection was just over three months.
When they looked at hospitalisation rates for chest infection, 50% of non-breastfed girls were hospitalised compared with 6.5% of breastfed girls; however, hospitalisation rates for non-breastfed and breastfed boys were equal (18.5 and 18.9% respectively). On statistical analysis, following adjustment for possible confounders, this gave girls a significant 95% decrease in risk of hospitalisation if they were breastfed. Breastfeeding also reduced the risk of increased episodes of hospitalisation by 98% in girls (though significance was borderline) but not in boys.
What interpretations did the researchers draw from these results?
The researchers conclude that “breastfeeding decreased the risk for severe lung disease in girls but not in boys”. They say that their results identify that non-breastfed premature girls may be a group particularly susceptible to severe lung disease, who may require special consideration.
What does the NHS Knowledge Service make of this study?
This is a carefully designed study that has aimed to establish whether breastfeeding confers any protection against severe lung disease in high-risk premature infants and whether there is any difference between girls and boys. However, there are several points that should be considered when interpreting results:
- This was a small study of only 119 infants. Much larger studies would be needed to confirm any results.
- The number of exclusively breastfeeding infants – only one boy and three girls – was too small a number to form any statistical comparisons. Other information on infant feeding is not detailed enough to be able to be conclusive about the effects of breastfeeding on infection. All other babies were grouped into breastfeeding ‘yes’ or ‘no’, but this would include a wide range of feeding patterns. Without detail on the number of feeds, it’s not possible to tell how much of the diet of infants was made up of breast milk and how much was formula and other supplements.
- The results are only applicable to low birth weight premature infants. As the researchers say, “the protective role of breastfeeding against severe respiratory infections in healthy term infants is well established”.
- Although results from this study appeared to show breastfeeding had a protective role against bronchiolitis in low birth weight girls but not boys, this should not be interpreted to mean that boys would have more protection from being bottle fed instead. The mechanisms of any protective effect of breastmilk against infection are not clearly established. It has traditionally been thought to be due to the transference of antibodies, although in that case it would be expected not to differ between genders. Whether there is any definite gender difference, or whether premature girls who are not breastfed may be at particular risk, is not clearly established and needs further research.
- The results cannot reliably be generalised outside of the study region. This study was conducted in Buenos Aires in clinics that care for low socioeconomic groups. The risk of chest infection, and of receiving hospitalisation for that chest infection, may be different among this group of infants from others of the same birth weight and prematurity in other countries where economy and care systems are different.
The numerous benefits of breastfeeding for both mother and baby are well established and breastfeeding should continue to be promoted as the healthiest start in life for both girls and boys.
Sir Muir Gray adds...
Breast is best for boys and girls.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 2 June 2008
The Guardian, 2 June 2008
Links to the science
Pediatrics 2008; 121:e1510-e1516