Age of cow milk introduction and growth among 3–5-year-old children

Objective: To evaluate the association between the age of cow milk introduction and childhood growth. Design: A secondary analysis of a prospective cohort study. Setting: Toronto, Canada. Participants: Healthy children <5 years of age enrolled in the TARGet Kids! practice-based research network. The primary exposure was the age of cow milk introduction. The primary outcome was height-for-age z-score. Secondary outcomes were volume of cow milk consumed (cups/d) and BMI z-score. Outcomes were measured at the last visit before 5 years of age. Multiple linear regression was used to examine these relationships. Results: Among 1981 children, introduction of cow milk at a younger age was associated with greater height by 3–5 years of age (P < 0·001). Each month earlier that cow milk was introduced was associated with 0·03 higher height-for-age z-score unit (95 % CI –0·05, –0·02) or 0·1 cm (95 % CI –0·15, –0·12 cm). At 4 years of age, the height difference between a child introduced to cow milk at 9 v. 12 months was 0·4 cm (95 % CI –0·45, –0·35 cm). There was no association between the timing of cow milk introduction and volume of cow milk consumed per day or BMI z-score. Conclusions: Earlier introduction of cow milk was associated with greater height but not with weight status in children aged 3–5 years. Further research is needed to understand the casual relationship between earlier cow milk consumption and childhood height. These findings may be important for paediatricians and parents when considering when to introduce cow milk.

Normal growth and its disorders

Normal growth has three phases: rapid in infancy and adolescence, steady during mid childhood. Height should always be interpreted within the context of the family: short or tall stature is often familial; idiopathic short stature occurs when the height of a normal child is below their target range. Constitutional growth delay is a common normal variant, but poor growth and/or weight gain may be associated with recognized and unrecognized chronic disease, and also with psychosocial deprivation. Investigation must exclude conditions including hypothyroidism, coeliac disease, inflammatory bowel disease, and chronic kidney disease. Turner syndrome (karyotype 45,X) should be suspected in all girls presenting with growth failure, and skeletal dysplasia when a child is either short for their family or has one parent of significant short stature.