Szajewska H. (2011) Am J Clin Nutr. Apr 27. [Epub ahead of print]
The role of early nutrition as a cost-effective measure to ensure optimal infant growth, development, and long-term health is gaining attention. In particular, the role of supplementation with nutrients such as n-3 (omega-3) fatty acids, iron, zinc, and B vitamins, which are relevant to brain structure and function, is of interest. However, for all of these nutrients, there is a lack of clarity and no consensus regarding their role in the mental and motor development of children.
Systematic reviews with or without a meta-analysis are a well-established means of reviewing existing evidence and of integrating findings from various studies, including those related to infant nutrition. In this article, I provide an overview of the basic principles of systematic review and meta-analysis of randomized controlled trials (RCTs) and summarize such evidence related to the effects of early nutrition on mental and motor development. The inclusion of only RCTs in a systematic review could be considered the major strength. Randomization is the only means to control for unknown and unmeasured differences between comparison groups as well as for those that are known and measured. However, even if only RCTs are included, reviews are not free of potential biases. An understanding of the strengths and limitations of the meta-analytic approach, which I discuss in this article, is needed by everyone involved in the decision making regarding interventions assessed by this approach.