Duration of Lactation is Associated with Lower Prevalence of the Metabolic Syndrome in Midlife — SWAN, the Study of Women's Health Across the Nation
Abstract & Commentary
By Sarah L. Berga, MD, James Robert McCord Professor and Chair, Department of Gynecology and Obstetrics, Emory University School of Medicine, Atlanta, is Associate Editor for OB/GYN Clinical Alert.
Dr. Berga reports no financial relationship to this field of study.
Synopsis: An analysis of SWAN data revealed a protective association between a history of lactation and metabolic syndrome, including an inverse dose-response relationship between duration of lactation and likelihood of developing metabolic syndrome at midlife.
Source: Ram KT, et al. Am J Obstet Gynecol. 2008;198:268.e1-268.e6.
The SWAN is a multisite, multi ethnic, prospective, observational, longitudinal study of 3302 women who were enrolled between 1995-1997. Eligibility for enrollment included age 42-52 years, intact uterus and at least one ovary, menses within the past 3 months, and not having taken reproductive hormones within the last 3 months. Ethnicity was categorized as African American, Caucasian, Chinese, Japanese, or Hispanic. The final analytic sample for this report included 2516 parous women who reported a live birth and duration of lactation.
Parous women who had ever breast-fed had a significantly lower prevalence of metabolic syndrome with an unadjusted odds ratio of 0.62 [0.51-0.75]. This association remained significant after adjusting for age, current smoking, parity, ethnicity, socioeconomic status, study site, physical activity, caloric intake, and high school BMI. Women who breast-fed their infants were significantly less likely to have impaired glucose (P < 0.01), elevated blood pressure (P = 0.05), and abdominal obesity (P < 0.01). Further, logistic regression showed that a dose-response relationship between duration of lactation and metabolic syndrome. These relationships held until women reported parity of 4 or more successful pregnancies.
Commentary
The metabolic syndrome is a clustering of metabolic aberrations, including insulin resistance, dyslipidemia, hypertension, and truncal obesity, that predisposes to diabetes mellitus and cardiovascular disease. Lifestyle factors, including poor nutrition, social stress, and physical inactivity have been implicated as causal factors. Smoking amplifies the cardiovascular risks of metabolic syndrome. The prevalence of metabolic syndrome and diabetes are rising exponentially around the globe, so understanding protective factors becomes ever more important.
This analysis was carefully conducted and the results are consistent across ethnic groups. Although women who breast feed are more likely to have healthier lifestyles in general, there are other biological factors that may mediate this association. Other studies have documented that in the immediate postlactional period, fasting plasma free fatty acids are lower both basally and during noradrenaline infusion. Other studies have also found that lactation altered fat deposition, decreased visceral adiposity, and increased insulin sensitivity. However, because pregnancy leads to weight retention, the metabolic benefits of lactation seem to diminish after more than 3 successful pregnancies.
There may be more to it than metabolism. Indeed, breastfeeding acutely reduces maternal reactivity to social stress and increases maternal awareness of infant needs. Research shows that motherhood alters the way social cues are processed by centers that mediate social intelligence such as the anterior cingulate cortex and lateral prefrontal cortex, leading to more nuanced social interactions. The duration of pregnancy- and breastfeeding-induced reductions in stress reactivity are unknown, but this is an area that can now be explored investigatively using state-of-the-art neuroimaging in the context of challenge paradigms. Again, it may be that motherhood and breastfeeding reduce stress reactivity, but only up to a point. We know that the number of children and the interval between them gates the risk for postpartum depression, with short intervals and multiple children increasing the risk.
In summary, the present article reinforces the notion that breastfeeding has many benefits for the mother as well as her infant.
The SWAN is a multisite, multi ethnic, prospective, observational, longitudinal study of 3302 women who were enrolled between 1995-1997.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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