Breast feeding and respiratory morbidity in infancy: a birth cohort study. (Original Article).

Aim: To examine the relation between the duration of breast feeding and morbidity as a result of respiratory illness and infection in the first year of life.

Methods: Prospective birth cohort study of 2602 live born children ascertained through antenatal clinics at the major tertiary obstetric hospital in Perth, Western Australia. Main outcome measures were hospital, doctor, or clinic visits, and hospital admissions for respiratory illness and infection in the first year of life. Main exposure measures were the duration of predominant breast feeding (defined as the age other milk was introduced) and partial (any) breast feeding (defined as the age breast feeding was stopped). Main confounders were gender, gestational age less than 37 weeks, smoking in pregnancy, older siblings, maternal education, and maternal age.

Results: Hospital, doctor, or clinic visits for four or more upper respiratory tract infections were significantly greater if predominant breast feeding was stopped before 2 months or partial breast feeding was stopped before 6 months. Predominant breast feeding for less than six months was associated with an increased risk for two or more hospital, doctor, or clinic visits and hospital admission for wheezing lower respiratory illness. Breast feeding for less than eight months was associated with a significantly increased risk for two or more hospital, doctor, or clinic visits or hospital admissions because of wheezing lower respiratory illnesses.

Conclusions: Predominant breast feeding for at least six months and partial breast feeding for up to one year may reduce the prevalence and subsequent morbidity of respiratory illness and infection in infancy.

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Breast feeding is clearly an issue for public health consideration as it provides significant protection against infections in newborns and infants. (1 2) Because breast feeding has been shown to protect against infections so profoundly in developing countries, it is estimated that an increase in breast feeding worldwide by 40% would reduce deaths from respiratory infection by 50% in children less than 18 months of age. (3)

Although breast feeding is associated with lower rates of both morbidity and mortality in the developing world, (2 4 5) evidence in the developed world has been and remains more controversial. (6 7) Yet, recent investigations show that respiratory tract infections (8-12) and asthma (13 14) are reduced in breast fed infants. On the other hand inverse relationships with breast feeding and health outcomes have been reported.

Respiratory infections and illness may be a risk factor for asthma in children (15) and their associated effects in relation to infant feeding need to be elucidated further. The effect of different feeding regimes was investigated in relation to respiratory infections and illness in a prospective birth cohort and following careful assessment of outcomes and exposures. We aimed to document the association of duration of predominant feeding and duration of any breast feeding with respiratory illness and infection morbidity as measured by doctor, hospital, or clinic visits and hospital admissions in the first year of life.

METHODS

Study population

The Western Australian Pregnancy Cohort Study was established between 1989 and 1992 as a prospective birth cohort study. (16) The cohort was serially recruited from the public antenatal clinic at King Edward Memorial Hospital, or nearby private practice in Perth, Western Australia. A total of 2979 women were enrolled at 18 weeks gestation. At the time of enrolment, data were collected from parents about their general and respiratory health and socioeconomic situation. By the end of the pregnancy phase 2888 women remained in the study, with 91 women having delivered elsewhere. Stillbirths and non-viable preterm births accounted for a further 28 pregnancies. Of 2860 live births, 13 infants (mostly neonates) had died, 154 had been withdrawn, and 81 (predominantly living overseas) had been lost to follow up. Thus 2602 out of 2860 (91%) children were available for follow up at 1 year of age. Informed consent was obtained for follow up of the children from birth.

Parents were provided with a diary card at the time of birth and were asked to complete the card on a daily basis throughout the first year by recording feeding history and illnesses. The illnesses recorded were those which required a visit to the hospital, doctor, or clinic, or hospital admission. At the end of the first year parents completed a questionnaire using the diary card as a prompt to recall events, (17) and their children were assessed for growth and development at the research clinic by a specially trained child health nurse. At the time of the one year assessment the nurse went through the questionnaire with the parent in a structured interview and transcribed feeding data as well as correct morbidity using ICD 9 codes for illnesses (age at completion of questionnaire: 13.9 (1.4) months).

At year one, 2456 questionnaires were received (82% of initial cohort; 94% of those consenting to follow up), and 2365 (79%; 91%) attended for clinical assessment. Of those parents who did not attend for clinical assessment (n = 91), questionnaire follow up was made by telephone.

Outcomes in the first year of life

Respiratory morbidity in the first year of life was the outcome of interest and included the number of doctor, hospital, or clinic visits, and the number of hospital admissions for any respiratory illness or infection. Respiratory illness and infection were grouped as upper respiratory tract infection (unspecified upper respiratory tract infections, tonsillitis, otitis media, otitis media with …