Meta-Analysis
Breastfeeding and the maternal risk of type 2 diabetes: A systematic review and dose–response meta-analysis of cohort studies

https://doi.org/10.1016/j.numecd.2013.10.028Get rights and content

Abstract

Background and aims

Breastfeeding has been associated with reduced risk of maternal type 2 diabetes in some cohort studies, but the evidence from published studies have differed with regard to the strength of the association. To clarify this association we conducted a systematic review and dose–response meta-analysis of breastfeeding and maternal risk of type 2 diabetes.

Methods and results

We conducted a systematic review and dose–response meta-analysis of prospective studies of breastfeeding and maternal risk of type 2 diabetes. We searched the PubMed, Embase and Ovid databases up to September 19th 2013. Summary relative risks were estimated using a random effects model. Six cohort studies including 10,842 cases among 273,961 participants were included in the meta-analysis. The summary RR for the highest duration of breastfeeding vs. the lowest was 0.68 (95% CI: 0.57–0.82, I2 = 75%, pheterogeneity = 0.001, n = 6). The summary RR for a three month increase in the duration of breastfeeding per child was 0.89 (95% CI: 0.77–1.04, I2 = 93%, pheterogeneity < 0.0001, n = 3) and the summary RR for a one year increase in the total duration of breastfeeding was 0.91 (95% CI: 0.86–0.96, I2 = 81%, pheterogeneity = 0.001, n = 4). There was little difference in the summary estimates whether or not BMI had been adjusted for. The inverse associations appeared to be nonlinear, pnonlinearity < 0.0001 for both analyses, and in both analyses the reduction in risk was steeper when increasing breastfeeding from low levels.

Conclusion

This meta-analysis suggests that there is a statistically significant inverse association between breastfeeding and maternal risk of type 2 diabetes.

Introduction

The prevalence of type 2 diabetes is increasing rapidly around the world parallel to the increase in obesity, reduction in physical activity and dietary changes. It has been estimated that 366 million people had diabetes (most of which are of type 2) in 2011 and the number has been projected to increase to 552 million by 2030 [1].

Breastfeeding exerts a major metabolic burden on mothers with an increase in the energy requirement of 400–600 kcal/d [2], [3], [4]. Several studies have reported reduced weight gain and abdominal fatness [5], [6], [7], [8], [9], improved insulin sensitivity [6], glucose tolerance [6], [10], and lipid metabolism [11] and reduced levels of C-reactive protein [12] in breastfeeding mothers. In addition, breastfeeding has been found to be associated with reduced circulating levels of inflammatory markers and increased levels of ghrelin and peptide YY [13]. Epidemiological studies have suggested reduced risk of maternal type 2 diabetes with breastfeeding and several, but not all of these found a stronger association with longer duration of breastfeeding [14], [15], [16], [17], [18]. However, the studies have differed somewhat with regard to the strength of the associations reported and it is not known what is the optimal duration of breastfeeding for prevention of maternal type 2 diabetes. To summarize the available data we conducted a systematic review and meta-analysis of cohort studies of breastfeeding and the risk of maternal risk of type 2 diabetes to clarify the size of the association, if there is a dose–response relationship between greater breastfeeding and type 2 diabetes risk, potential confounding from other risk factors, and whether this partly might be explained by reduced postpartum weight retention by comparing risk estimates adjusted and not adjusted for BMI.

Section snippets

Search strategy

We searched the PubMed, Embase and Ovid databases up to September 19th 2013 for published studies of breastfeeding and type 2 diabetes risk. We used the search terms (“breastfeeding” OR “lactation”) AND diabetes in the search. We scrutinized the references of the identified reports for any further studies. Unpublished data, abstracts, or grey literature was not included. We followed standard criteria for meta-analyses of observational studies [19].

Study selection

To be included, the study had to have a

Results

We identified 6 cohort studies (5 publications) [14], [15], [16], [17], [18] that could be included in the meta-analysis of breastfeeding and type 2 diabetes, including 10,842 cases among 273,961 participants (Table 1, Fig. 1). The number of subjects in each study ranged from 304 to 83,585 and the number of cases ranged from 147 to 3160. One of the studies was conducted among women with gestational diabetes mellitus, two of the studies among American nurses and three studies among women from

Discussion

We found that the longest duration of breastfeeding compared to no breastfeeding was associated with a 32% reduction in the relative risk of type 2 diabetes. In linear dose–response analyses there was a 9% reduction in relative risk for each 12 month increase in lifetime duration of breastfeeding and a non-significant 11% reduction in relative risk for each 3 month increase in duration of breastfeeding per child. There was evidence of nonlinearity in both analyses and the reduction in risk was

Duality of interest

The authors declare that there is no duality of interest associated with this manuscript.

Contribution statement

DA designed the project, conducted the literature search and analyses and wrote the first draft of the paper. DA, TN, PR, LJV interpreted the data, revised the subsequent drafts for important intellectual content and approved the final version of the paper to be published.

Acknowledgment

This project has been funded by Liaison Committee between the Central Norway Regional Health Authority (RHA) and the Norwegian University of Science and Technology (NTNU).

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