母乳喂养或可降低亚洲儿童肥胖风险

《美国医学会杂志-儿科》8月12日在线发表的一篇报告显示，根据对超过6万名日本儿童的分析，接受至少6个月母乳喂养的儿童在7~8岁时超重或肥胖的风险，显著低于接受配方奶喂养的儿童(JAMA Pediatr. 2013 [doi:10.1001/jamapediatrics.2013.2230])。

主要研究者、日本冈山大学流行病学系的山川美智代指出，母乳喂养与肥胖的关联最强。具体而言，单纯母乳喂养至少6个月与童年肥胖风险降低45%、超重风险降低15%有关。



既往多项研究显示，母乳喂养具有对抗童年肥胖的保护作用，多数研究报告称风险可降低15%~20%。但近期若干项研究(包括唯一的另一项针对亚洲人群的相关研究)的结论是，母乳喂养不具有预防儿童肥胖的作用，这种不一致可能是母乳喂养相关因素(例如社会经济地位、饮食习惯、体力活动水平和吸烟状态等母亲因素)引起混淆的结果。

山川美智代及其同事利用一个大型全国数据库探讨了这一问题。这项名为“21世纪婴儿纵向调查”的研究从2001年开始收集家长提供的关于家庭环境、育儿方式和儿童健康、发育的数据，目前仍在进行中。

本次发表的分析涉及29,907名7岁儿童和30,780名8岁儿童，其家长从儿童6个月大时开始参与调查。所有受试者均未单胎足月儿。利用这些数据，研究者计算了受试者目前体重指数、看电视时间、玩电脑游戏时间，并且评估了家长的营养知识、母亲的受教育程度、吸烟状态和工作状态。

结果显示，超过20%的受试者接受了至少6个月单纯母乳喂养，超过70%在此期间接受了部分母乳喂养。仅有5%~6%的儿童曾接受单纯配方奶喂养。研究者指出，日本社会强烈鼓励母乳喂养，这可能是上述比例与西方国家差异较大的原因之一。

在7岁组中，7.3%的儿童超重，2.1%肥胖。超重和肥胖的流行率均随着母乳喂养时间延长而降低，呈现出剂量依赖关系。在校正多种混淆因素的影响之后，母乳喂养的抗超重/肥胖保护效应仍然保持着显著性。

8岁组得出了相似结果：超重率和肥胖率分别为7.8%和1.9%，二者均随着母乳喂养时间延长而降低，这一相关性在校正多种混淆因素后仍然显著。

这项研究获得了日本厚生劳动省和住友基金会的经费支持。研究者无利益冲突披露。

随刊述评：对文献的有益补充

Marit L. Bovbjerg博士、Carolina Amador博士和Adrienne E. Uphoff在随刊述评中指出，山川美智代等人的研究是“对文献的有益补充”，原因是它首次在亚洲人群中探讨了母乳喂养与儿童肥胖的关联(JAMA Pediatr. 2013 [doi:10.1001/jamapediatrics.2013.2854])。

这也可能是首个关于这一问题的真正以人群为基础的研究。它纳入了在2001年的2周内出生的所有日本儿童，其家长88%参加了这项调查。因此该研究有力地印证了既往很多研究的结果：母乳喂养对童年超重和肥胖具有预防作用。

Bovbjerg博士供职于俄勒冈州立大学公共卫生与人类科学学院，Amador博士供职于俄勒冈州Benton和Linn郡社区卫生服务中心，Uphoff女士供职于夏洛茨维尔Skyline哺乳护理中心和弗吉尼亚联邦大学。

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By: MARY ANN MOON, Clinical Endocrinology News Digital Network

Japanese children who were breastfed for at least 6 months had a significantly lower risk of overweight and obesity at ages 7 and 8 years than did those who were formula fed, according to an analysis of more than 60,000 children that was reported online August 12 in JAMA Pediatrics.

This association was strongest for obesity. In particular, exclusive breastfeeding for at least 6 months was associated with a 45% decreased risk of childhood obesity and a 15% decreased risk of childhood overweight, said Michiyo Yamakawa of the department of epidemiology, Okayama (Japan) University, and her associates.

Many previous studies have shown that breastfeeding exerts a protective effect against childhood obesity, with most reporting a 15%-20% reduction in risk. But a few recent studies, including the only other study to assess this relationship in an Asian population, concluded that there was no protective effect and that findings to the contrary most likely reflect confounding by other factors associated with breastfeeding, such as socioeconomic status, dietary habits, physical activity levels, and such maternal factors as smoking status.

Ms. Yamakawa and her colleagues examined this issue using a large, nationwide database that allowed for control of many important confounders. The ongoing Longitudinal Survey of Babies in the 21st Century has collected reports from parents on family circumstances, child-rearing practices, and children’s health and development throughout Japan since 2001 (JAMA Pediatr. 2013 [doi:10.1001/jamapediatrics.2013.2230]).

For this study, the researchers focused on 29,907 7-year-old and 30,780 8-year-old children whose families participated in the surveys when the children were 6 months of age. All the study subjects were singleton infants born at term.

The data allowed the investigators to calculate the children’s current body mass index, and also included their television viewing time; their computer game–playing time; the parents’ knowledge of nutritional matters; and maternal educational attainment, smoking status, and employment status.

More than 20% of this study population had been exclusively breastfed for at least 6 months, and more than 70% had been partially breastfed for that length of time. Only 5%-6% of the children had been exclusively formula-fed. Japanese society strongly promotes breastfeeding, which may account for the difference in prevalence between this study population and typical Western populations, they noted.

In the 7-year-old group, 7.3% were overweight and 2.1% were obese. The prevalence of both of overweight and obesity decreased as the duration of breastfeeding increased, showing a dose-response relationship.

After the data were adjusted to account for several confounders, the protective effect of breastfeeding against overweight and obesity still remained significant.

The results were similar in the 8-year-old group, in which 7.8% were overweight and 1.9% were obese. Here again the prevalence of both conditions decreased as the duration of breastfeeding increased, and the association remained significant even after adjustment for several confounders.

This study was supported by grants from the Japanese Ministry of Health, Labour, and Welfare, and the Sumitomo Foundation. No financial conflicts of interest were reported.

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A novel, helpful addition to the literature

The work by Yamakawa et al. is "a novel and helpful addition to the literature," because it is one of the first studies to explore the relationship between breastfeeding and obesity in an Asian population, said Marit L. Bovbjerg, Ph.D., Dr. Carolina Amador, and Adrienne E. Uphoff.

This also may be the first true population-based study of the issue, with a cohort comprising all children born in Japan during 2 distinct weeks in 2001, and with 88% of parents participating in the survey. So it is reassuring that this study found what many previous studies have reported: Breastfeeding is protective against childhood overweight and obesity, they said.

Dr. Bovbjerg is at the College of Public Health and Human Sciences at Oregon State University, Corvallis. Dr. Amador is at Community Health Centers of Benton and Linn Counties, Corvallis, Ore. Ms. Uphoff is at Skyline Lactation Care in Charlottesville, Va., and Virginia Commonwealth University, Richmond. These remarks were taken from their editorial accompanying Ms. Yamakawa’s report (JAMA Pediatr. 2013 [doi:10.1001/jamapediatrics.2013.2854]).