Introduction

In order to achieve optimal young child growth and development, WHO recommends that infants be exclusively breastfed for the first six months of life (1). Thereafter, infants should receive nutritionally adequate and safe complementary foods with continued breastfeeding up to 2 years of age or beyond (2). Indicators for assessing infant and young child feeding practices include continued breastfeeding at one year as a core indicator and continued breastfeeding at two years as an optional indicator (3). Indeed, continued breastfeeding is much more common in children at one year than at two years of age. An analysis of the Demographic Health Survey data available from 46 low- and middle-income countries found that while 72% of those countries had at least 80% of children breastfed at 1 year, just 11% had at least 80% of children still being breastfed at 2 years (4).

Continued breastfeeding is much more common in low- and middle-income countries than it is in high-income countries. A recent study found that in most high-income countries the prevalence of breastfeeding at one year is lower than 20% (5). The lowest breastfeeding prevalence rates were recorded in the UK (0.5%), Ireland (2%), Saudi Arabia (2%), Denmark (3%), Greece (6%) and France and Canada at 9%. In contrast, most of the 126 low- and middle-income countries (86%) had more than half of their one year olds still breastfeeding. There however exists large variation within national data, and in the USA for example, where about a quarter of children are still breastfeeding at one year of age, the practice ranges from 10% in Mississippi to up to 45% in Vermont (6).

Breastfeeding is not only the best way of providing food for the healthy growth and development of infants, but is also an integral part of the reproductive process with important implications for the health of mothers (1). The benefits to the child of exclusive breastfeeding for the first six months are reasonably well established in terms of morbidity and mortality (7). The benefits of continued breastfeeding are less well established however (8). Studies in developing countries demonstrate that continued, frequent breastfeeding is associated with greater linear growth and further protects child health by delaying maternal fertility postpartum and reducing the child’s risk of morbidity and mortality. The purpose of this commentary is to explore the evidence relating to the benefits of continued breastfeeding to both mother and child. To do this, the systematic review and meta-analysis of breastfeeding and maternal health outcomes by Chowdhury et al. (9), of optimal breastfeeding practices and infant and child mortality by Sankar et al. (10), and of breastfeeding and childhood obesity by Yan et al. (11), are analysed and their findings revisited.

Methodology summary

All three reviews conducted systematic literature searches in appropriate data bases such as PubMed, Cochrane Library and CABI and included prospective and/or retrospective cohort and case control studies, as well as randomized or quasi-randomized controlled trials with or without blinding. After reviewing titles and abstracts of studies found and eliminating duplicates, the full papers were reviewed in order to independently assess trial eligibility. Of the selected trials, quality was assessed and data extracted where available; trial investigators were contacted as necessary for additional information. Outcome estimates of odds ratios, relative risks or standardized mean differences were pooled. In cases of heterogeneity, subgroup analysis was carried out using fixed and random effects models and meta-regression where possible.

Evidence summary

The Chowdhury et al. (9) review found that continued breastfeeding protects mothers against breast and ovarian cancer and possibly type 2 diabetes. Their review, conducted in February 2015, identified 12,041 non-duplicated titles with 1501 selected for abstract review and 341 chosen for full text review. Based on 50 studies, it was found that mothers who breastfed for more than 12 months had a 26% reduced risk of breast cancer compared to those who had never breastfed. When restricted to 41 high quality studies, this risk was reduced to 23%. Continued breastfeeding was also found to result in a 28% reduced risk of ovarian cancer among mothers who breastfed for 6-12 months (19 studies) and 37% reduced risk among mothers who breastfed for more than 12 months (29 studies). Furthermore, longer duration of breastfeeding was associated with a reduced risk of type 2 diabetes development by 32% and based on dose-response analyses there was a 9% reduction in relative risk of diabetes for each 12-month increase in lifetime duration of breastfeeding. There was no clear evidence of the effect of breastfeeding on osteoporosis risk.

The Sankar et al. (10) review found that continued breastfeeding protects against all-cause mortality in the first two years of life. Their review, which included articles up to October 2014, identified 1330 non-duplicated titles. Of these, 762 were selected for abstract review, 77 for full text review and 13 were included in quantitative synthesis. When any breastfeeding was compared with no breastfeeding in infants aged 6-12 months (4 studies) and those aged 12-23 months (6 studies) the risk of mortality was 1.8- and 2.0-fold greater respectively.

The Yan et al. review (10) found that breastfeeding is a significant protective factor against obesity in children. Their review revealed 428 unduplicated articles published up to August 2014. Of these, a total of 25 studies involving 226,508 subjects were included in the meta-analysis. While breastfeeding for less than 3 months provided a minor protective effect, breastfeeding for 7 months or more showed a significantly high protection against childhood obesity. The risk of childhood obesity was reported to be lower in breastfed children by 22% compared with those who were never breastfed (10).

Discussion

Taken together, the results of these three systematic reviews all point to the beneficial effects of continued breastfeeding beyond six months for both mother and child. The protective effects of breastfeeding for mothers include reduced risk of both ovarian and breast cancer as well as type 2 diabetes. The benefits to infants include reduced risk of all-cause mortality and obesity.

Applicability of the results

The results of these three systematic reviews seem to be largely applicable to most settings despite disparities in the quality of the evidence. The findings of the Chowdhury et al. (9) review where ovarian cancer was an outcome included studies from 30 countries. While there was evidence of publication bias, subgroup analysis among studies conducted in high-income countries with large sample sizes showed a smaller, but still significantly increased risk of cancer. Furthermore, the results for ovarian cancer showed no sign of such bias. Evidence for the type 2 diabetes review conducted by Aune et al. (12) which was included in the Chowdhury et al. (9) review showed no significant heterogeneity between subgroups when studies were stratified by geographic location, number of cases, or study quality scores. Furthermore, the inverse association between breastfeeding and type 2 diabetes appeared to be independent of other important risk factors such as BMI, smoking, alcohol, physical activity, education, income, parity and family history of diabetes. The Sankar et al. review (10) which examined the effect of continued breastfeeding on child mortality was restricted to studies carried out in low and middle-income countries, and the quality of the evidence was considered to be low, largely due to the inclusion of observational studies. The Yan et al. (11) review of breastfeeding and childhood obesity showed little evidence of such biases, with no differences in pooled estimates across cohort and cross sectional studies. When taken together, the results of the three reviews are largely consistent and broadly applicable.

Implementation in settings with limited resources

The implementation of interventions to promote continued breastfeeding is most needed in high-income settings and in urban areas in low- and middle-income countries where continued breastfeeding prevalence is relatively lower. The need for women to return to work is a leading contributor to the decision to discontinue breastfeeding early. In addition, social and cultural attitudes and market factors also play a contributing role (12). Continued breastfeeding improves with home- and family-based interventions, such as home visits by community health workers and counselling of fathers. Maternity protection legislation ensuring maternity leave, as well as the reduction of barriers for working mothers to breastfeed such as the provision of lactation rooms and breaks to express milk in the workplace can help increase continued breastfeeding beyond six months. Proper regulation of the breast-milk substitute industry and enforcement of the International Code of Marketing of Breast-milk Substitutes is also an essential element for promoting and protecting continued breastfeeding.

Further research

All three of the reviews point to the need for future research. The scope of reviews and studies looking at maternal health should be expanded to include maternal hypertension and cardiovascular disease. Future studies looking at continued breastfeeding and childhood obesity would benefit from using more than one indicator of obesity as well as the use of internationally accepted breastfeeding indictors. More research is needed into the effectiveness of interventions that promote continued breastfeeding, for example, at present there exists no study examining the effect of community level interventions on continued breastfeeding (13). More research is needed into the costs of policies and programmes that enable continued breastfeeding, including maternity entitlements, as compared to the economic and environmental benefits of continued breastfeeding.

References

1. WHO recommendations on postnatal care of the mother and newborn. Geneva: World Health Organization; 2014.(https://www.who.int/maternal_child_adolescent/documents/postnatal-care-recommendations/en/)

2. WHO/UNICEF. Global strategy on infant and young child feeding. Geneva: World Health Organization; 2003. (https://www.who.int/nutrition/publications/infantfeeding/9241562218/en/)

3. WHO/UNICEF/IFPRI/UC Davis/USAID/FANTA. Indicators for assessing infant and young child feeding practices. Part 1: definitions. Geneva: World Health Organization; 2008. (https://www.who.int/nutrition/publications/infantfeeding/9789241596664/en/)

4. WHO/UNICEF/IFPRI/UC Davis/USAID/FANTA. Indicators for assessing infant and young child feeding practices. Part 3: country profiles. Geneva: World Health Organization; 2008. (http://www.who.int/nutrition/publications/infantfeeding/9789241599757/en/)

5. Victora CG, Bahl B, Barros AJD, França GVA, Horton S, Krasevec J et al. for The Lancet Breastfeeding Series Group. Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect. Lancet. 2016;387: 475–90.

6. National Center for Chronic Disease Prevention and Health Promotion. Breastfeeding Report Card. United States/2014. Atlanta: Centers for Disease Control and Prevention; 2014. (https://www.cdc.gov/breastfeeding/pdf/2014breastfeedingreportcard.pdf)

7. Kramer MS, Kakuma R. Optimal duration of exclusive breastfeeding. Cochrane Database Syst Rev. 2012;8: CD003517.

8. Guiding principles for complementary feeding of the breastfed child. Washington, DC: Pan American Health Organization; 2003. (https://www.who.int/maternal_child_adolescent/documents/a85622/en/)

9. Chowdhury R, Sinha B, Sankar MJ, Taneja S, Bhandari N, Rollins N, Bahl R, Martines J. Breastfeeding and maternal health outcomes: a systematic review and meta-analysis. Acta Paediatr. 2015;104(467):96-113.

10. Sankar MJ, Sinha B, Chowdhury R, Bhandari N, Taneja S, Martines J, Bahl R. Optimal breastfeeding practices and infant and child mortality: a systematic review and meta-analysis. Acta Paediatr. 2015;104(467):3-13.

11. Yan J, Liu L, Huang G, Wang PP. The association between breastfeeding and childhood obesity. BMC Public Health. 2014;14:1267.

12. Aune D, Norat T, Romunsdstad P, Vatten LJ. Breastfeeding and the maternal risk of type 2 diabetes: A systematic review and dose-response meta-analysis of cohort studies. Nutr Metab Cardiovasc Dis. 2014;24(2):107-15.

13. Rollins NC, Bhandari N, Hajeebhoy N, Horton S, Lutter CK, Martines JC, Piwoz EG, Richter LM, Victora CG, for the Lancet Breastfeeding Series Group. Why invest and what it will take to improve breastfeeding practices? Lancet. 2016;387:491-504.

Disclaimer

The named authors alone are responsible for the views expressed in this document.

Declarations of interests

Conflict of interest statements were collected from all named authors and no conflicts were identified.