Maternal smoking and reduced duration of breastfeeding: a review of possible mechanisms
Introduction
It is well recognised that women who smoke are less likely to breastfeed than non-smokers [1], [2]. The mechanism for this may be physiological and/or social, but critical review in this area is lacking.
It has been generally accepted that nicotine in the mother's blood stream reduces the level of prolactin, the hormone closely associated with lactation [3], [4]. However, recent studies have thrown doubt over the importance of prolactin in the ongoing production of breast milk [5].
Another widely accepted belief is that smoking interferes with the release of oxytocin, the hormone responsible for the milk ejection reflex (or let-down) [6]. The evidence for this will be reviewed, and an alternative understanding of the mechanism of how smoking may affect lactation will be presented.
The aim of this paper is to systematically review the possible mechanisms by which cigarette smoking may affect lactation. Publications in the areas of biochemistry, physiology, pathology, psychology and clinical practice have all been included in order to expand the understanding of the relationship between maternal smoking, lactation and behaviour. Studies in animal models have been included because, firstly, their findings have been extrapolated to humans and, secondly, research in women is sparse. Directions for future research in the area of smoking and breastfeeding will be considered. A second paper has reviewed epidemiological studies to examine the effect of maternal smoking on initiation and duration of breastfeeding (Amir and Donath, in preparation).
Section snippets
Background
It is thought that the first report of an adverse effect of maternal smoking on breastfeeding was published by Mills in 1950 [7]. Although many studies have not accounted for the socio-demographic differences between women who smoke and non-smokers [2], large studies have found an association between maternal smoking and artificial feeding, which remains after adjusting for confounding factors [3], [8], [9], [10], [11].
Tobacco smoke contains at least 3800 components, of which nicotine is the
Method
The following data sources were used to identify articles or book chapters reporting maternal smoking and the effect on lactation:
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The Cochrane Library
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Medline, CINAHL, Current Contents, Psychinfo and Sociological Abstracts
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Lactation Resource Centre, Nursing Mothers' Association of Australia
Key words were “smoking” and “breastfeeding” or “infant feeding”, and searches were conducted from the start of the database to Week 4 2001 (Medline, Current Contents), Nov. 00 (Psychinfo), Oct. 00 (CINAHL),
Hormonal effects of smoking on the mother
Table 1 is a collection of studies that have investigated the relationship between smoking and maternal hormone levels. The rat studies found that animals exposed to nicotine had lower levels of prolactin or blockage of prolactin release and impaired lactation compared to controls. Blake and Sawyer state that “Although the smoker's consumption of nicotine would certainly be less than our rat's intake on a per kilogram basis, species differences can make weight-basis comparisons meaningless” (p.
Physiological factors
Hormonal studies of animal models are included in Table 1 because these are widely cited as evidence for the reduced duration of breastfeeding in human smokers [4], [35], [36]. The studies of hormones and nicotine were conducted prior to 1986, and it appears that investigations have not continued in this area. The observations of rats and mice have been made on small samples and the conditions of the studies are contrived. The validity of extrapolating from animal studies to human populations
Conclusion
There are a number of possible explanations for an adverse effect of maternal smoking on breastfeeding. These include a physiological effect of nicotine on the mother's hormonal system or on her breasts directly, or the infant may be directly affected and have difficulty feeding or show irritable behaviour. The mechanism is generally thought to be lowering of prolactin by nicotine, however, the long-term levels of prolactin do not correlate with milk production. The possibility that nicotine
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2020, European Journal of Obstetrics and Gynecology and Reproductive BiologyCitation Excerpt :Participants who were breastfed had significantly lower odds of endometriosis compared to those not breastfed (OR = 0.39, 95 % CI = 0.21−0.74) (Table 3). Since maternal smoking can be associated with the choice or ability to breastfeed or not [37], we additionally adjusted for smoking status of the participants’ mother during pregnancy and observed nearly identical results (OR = 0.40, 95 %CI = 0.21−0.76). A higher proportion of participants were breastfed among those whose mother did not have a history of endometriosis (82 % vs 72 %), with the same protective pattern of breastfeeding within this group (OR = 0.31, 95 % CI = 0.16−0.63).
Hypothesis: Smoking decreases breast feeding duration by suppressing prolactin secretion
2013, Medical HypothesesCitation Excerpt :If smoking does indeed suppress breast feeding duration, this could be expected to have important health implications both for the infant and the mother; prolonged breast feeding is associated with decreased maternal risk for breast and ovarian cancer, and possibly metabolic syndrome, and breast-fed infants are at lower risk for a number of types of infections [16–19]. Nevertheless, some commentators have suggested that smoking per se does not notably influence lactation, but rather that motivational factors can account for lesser breast feeding duration in smokers [20–24]. In other words, women who do not smoke, or who are willing and able to quit smoking post-natally, simply have better self-control and a more intelligent regard for their own welfare and that of their infant which translates into a greater willingness to commit to long-term breast feeding.
Maternal diet and breastfeeding: A case for rethinking physiological explanations for breastfeeding determinants
2012, Early Human DevelopmentCitation Excerpt :However, we may have been too cautious in our carefully worded conclusions: “Conclusion: Although there is consistent evidence that women who smoke breastfeed their infants for a shorter duration than non-smokers, the evidence for a physiological mechanism is not strong” [8 p. 45]; “Therefore, it is likely that psychosocial factors are largely responsible for the lower rates of breastfeeding found in women who smoke compared to those who do not smoke”. [2 p. 121]
Co-use of tobacco and marijuana during pregnancy: Pathways to externalizing behavior problems in early childhood
2018, Neurotoxicology and TeratologyCitation Excerpt :Breastfeeding is a particularly important early experience that serves a protective role for infant development (Horta et al., 2007) and maternal health (Chung et al., 2007; U.S. Department of Health and Human Services, 2011). The Center for Disease Control and Prevention (2009) recommends breastfeeding even when a mother continues to smoke; however, women who smoke report breastfeeding for shorter durations and being less likely to intend to breastfeed and to initiate breastfeeding than non-smoking women (Liu et al., 2006; for review see Amir, 2001; Amir and Donath, 2002; Horta et al., 2001). In fact, a dose-response relation between number of cigarettes smoked and duration of breastfeeding was demonstrated (see Amir and Donath, 2002).