A recent publication in the American Journal of clinical nutrition presents the results of a study on the dietary intake of cow’s milk and non-cow’s milk beverages in children aged 24-72 months. The authors conclude that non-cow’s milk consumption is associated with lower childhood height.
There are multiple issues with the methodology used in this study that cast doubt on the value of its results and conclusions.
• The paper compares 4,632 cow’s milk drinkers with 643 non-cow’s milk drinkers. However, within these two groups there are 397 children consuming both cow and non-cow’s milk, meaning that only 4.8% (246) children in the study consume only non-cow’s milk.
o Additionally, data from the children consuming both cow’s and non-cow’s beverages are included in both groups and therefore the data are counted twice in the analysis.
• Non-cow’s milk is defined as any other type of milk not based on cow’s milk and included both plant and animal beverages e.g. goat’s milk, alongside soya and nut beverages which all have very different nutritional values. Additionally, many plant-based beverages are now fortified with vitamins and minerals. The authors therefore are completely unware of the nutritional values of the non-cow’s milk beverages and for the plant-based varieties, whether or not they were fortified nor can they make any connection between the groups for the quality and quantity of protein.
• The authors did not take other dietary factors into account. They propose that one of the key reasons why cow’s milk is important for height is achieving adequate protein intakes. Yet, without a full dietary analysis, they cannot be aware which children met their protein requirements and which did not. There are also many other protein sources in young children’s diets.
• The authors only adjusted data for maternal height but not for paternal height. The height of both parents should have been taken into account.
• The only dietary intake collected was how many 250ml cups of cow’s milk or non-cow’s milk was consumed per day. This was undertaken by questionnaire, which may be subject to measurement error or recall bias.
• It is not known when the children started consuming the non-cow’s milk drinks, or why they were consuming non-cow’s milk, both of which could have a significant effect on the results observed.
• The authors also recognise a potential height measurement error given the young age of the children.
• Finally, it is a cross-sectional study, not designed to look for causal effect, and thus the simplistic conclusion that height is effected by milk type cannot be drawn.
Our key take outs
Overall, the study is misleading and no conclusions can be drawn except that it is important for parents to be educated on children’s nutrition. Parents of children wishing or needing to avoid cow’s milk should seek dietetic advice to ensure that suitable alternatives are used and the nutritional quality of their overall diet is balanced. There is no reason why a healthy child following a balanced diet should not include calcium and vitamin fortified plant-based beverages. Additionally, soya beverages are similar to cow’s milk for protein quality and quantity.
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