Abstract
I
Breast milk is the optimal food source for infants containing not only nutrients but also an array of bioactive substances. 7,8 Pregnancy and early postpartum metabolic status of women are known to influence the breast milk composition. For example, breast milk from women with glucose intolerance and obesity has higher insulin concentrations. 9 These hormones in breast milk may regulate tissue activities of infants while the endocrine system matures and may subsequently contribute to the long-term health, such as the documented association between breastfeeding and lower risk for metabolic disease in the offspring. 10 In addition to the impact on the offspring health, growing evidence suggests that breastfeeding may also have long-term consequences on lactating mothers. 10 Women with longer lifetime duration of lactation are at a lower risk for hypertension, thyroid complication, hyperlipidemia, type 2 diabetes, and cardiovascular disease. 11 –13
In this issue of Journal of Women's Health, Rajaei et al. 14 add to this growing evidence with a report indicating that parous women who breastfeed a child for longer than 5 months are at lower risk for coronary artery disease later in life. They conclude this after administering a survey about women's reproductive and lactation history from >600 women aged 40–65 years who were outpatients of Internal Medicine or Cardiology Clinic at a teaching hospital. This study setting uniquely allowed data collection of clinically confirmed coronary artery disease cases and traditional risk factors such as measured body weight, blood pressure, and lipids through the participants' medical record.
Although the study has its methodological strengths and contributes to the current knowledge, there are limitations to the current findings that hold relevance for future investigations. First, the cross-sectional observational study design limits from offering causal or mechanistic explanations for the observed association. Although the randomized control trial design is methodologically ideal, it is not ethical to randomize breastfeeding behavior. However, additional insights may be gained through carefully designed prospective or experimental studies in the future. Second, recruiting study participants who were already patients of cardiology clinic might have introduced bias in women's recalls. Although this recruitment strategy allowed a large proportion of cases to be captured within the modest sample size of about 600 women, this may have inflated the result estimates, complicating the direct interpretation of the findings. Hence, future studies are warranted in a larger sample-sized healthy-living population. Third, although the investigators were able to collect information on duration of breastfeeding for each live birth, the detailed breastfeeding behaviors such as exclusivity were not reported. Since the intensity of lactation behavior may influence the postpartum recovery of maternal metabolic status, this requires further investigations. Fourth, although this study was able to capture the medical history at the time of the lactation history survey, many other modifiable risk factors for coronary artery disease such as diet and lifestyle were not considered. Since these modifiable factors may offer potential to intervene the course of the disease progression, these are important areas for future studies to explore.
In summary, the study by Rajaei et al. 14 provides data further supporting the role of lactation behavior on women's cardiometabolic health later in life. It also raises additional questions to be addressed, including potential mechanistic pathways involved in such association, implications of intensity of lactation behavior, and revenues for intervention strategies. Although the current recommendation calls for putting children to the breast immediately after birth, breastfeeding exclusively for the first 6 months of life, and continuing to breastfeed for 2 years and beyond, we continue to fall behind in meeting these in practice with the latest global report of only 42% breastfeeding initiation within the first hour of birth. 15 Continued investigation on the long-term consequences of breastfeeding is warranted from the perspectives of not only the receiving children but also the breastfeeding mothers.