The Motherisk Program, Hospital for Sick Children, Toronto, Ontario, Canada.
BMJ Open. 2013 Aug 23;3(8):e003259. doi: 10.1136/bmjopen-2013-003259.
The association between breastfeeding and child cognitive development is conflicted by studies reporting positive and null effects. This relationship may be confounded by factors associated with breastfeeding, specifically maternal socioeconomic class and IQ.
Systematic review of the literature.
Any prospective or retrospective study, in any language, evaluating the association between breastfeeding and cognitive development using a validated method in healthy term infants, children or adults, was included.
Extracted data included the study design, target population and sample size, breastfeeding exposure, cognitive development assessment tool used and participants' age, summary of the results prior to, and following, adjustment for confounders, and all confounders adjusted for. Study quality was assessed as well.
84 studies met our inclusion criteria (34 rated as high quality, 26 moderate and 24 low quality). Critical assessment of accepted studies revealed the following associations: 21 null, 28 positive, 18 null after adjusting for confounders and 17 positive-diminished after adjusting for confounders. Directionality of effect did not correlate with study quality; however, studies showing a decreased effect after multivariate analysis were of superior quality compared with other study groupings (14/17 high quality, 82%). Further, studies that showed null or diminished effect after multivariate analysis corrected for significantly more confounders (7.7±3.4) as compared with those that found no change following adjustment (5.6±4.5, p=0.04). The majority of included studies were carried out during childhood (75%) and set in high-income countries (85.5%).
Much of the reported effect of breastfeeding on child neurodevelopment is due to confounding. It is unlikely that additional work will change the current synthesis. Future studies should attempt to rigorously control for all important confounders. Alternatively, study designs using sibling cohorts discordant for breastfeeding may yield more robust conclusions.
母乳喂养与儿童认知发展之间的关系存在争议，一些研究报告称母乳喂养具有积极影响，而另一些研究则认为其没有影响。这种关系可能受到与母乳喂养相关的因素的影响，特别是母亲的社会经济地位和智商。
文献系统综述。
任何评估母乳喂养与认知发展之间关系的前瞻性或回顾性研究，无论语言如何，只要使用经过验证的方法评估健康足月婴儿、儿童或成人，均被纳入。
提取的数据包括研究设计、目标人群和样本量、母乳喂养暴露、使用的认知发育评估工具以及参与者的年龄、调整混杂因素前后的结果总结，以及所有调整混杂因素后的结果。还评估了研究质量。
84 项研究符合我们的纳入标准（34 项评为高质量，26 项为中等质量，24 项为低质量）。对公认研究的严格评估显示出以下关联：21 项无关联，28 项有积极关联，18 项在调整混杂因素后无关联，17 项在调整混杂因素后积极关联减弱。效应的方向性与研究质量无关；然而，与其他研究分组相比，在多变量分析后显示效果减弱的研究质量更高（14/17 项为高质量，82%）。此外，在多变量分析后，那些校正了更多混杂因素（7.7±3.4）后显示无变化或效应减弱的研究（5.6±4.5，p=0.04）比那些在调整后没有变化的研究校正了更多混杂因素（7.7±3.4）。纳入的大多数研究都是在儿童时期进行的（75%），并且在高收入国家进行（85.5%）。
母乳喂养对儿童神经发育的影响很大程度上是由于混杂因素造成的。进一步的研究不太可能改变目前的综合结果。未来的研究应尝试严格控制所有重要的混杂因素。或者，使用母乳喂养不一致的兄弟姐妹队列的研究设计可能会得出更可靠的结论。
