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.