Maternal smoking and reduced duration of breastfeeding: a review of possible mechanisms

Aim: To systematically review the possible mechanisms by which maternal smo king affects lactation. Methods: Databases (Medline, CINAHL, Current Conten ts, Psychinfo, Sociological Abstracts and the Cochrane Library) were search ed for smoking and breastfeeding or infant feeding. The Journal of Human La ctation and Birth were hand-searched, searches were also conducted at NMAA' s Lactation Resource Centre and references cited were located where appropr iate. Articles were divided into the various ways that smoking could affect breastfeeding and were tabulated. Results: Most studies were conducted on small samples of animals or humans; the majority were prior to 1985. Most a nimal studies exposed the animals to much greater levels of nicotine than t hose to which humans are exposed. Most studies did not examine if breastfee ding behaviour was similar in smokers and non-smokers, and did not consider that any physiological difference found could be the result of poor lactat ion practices, rather than the cause of poor lactation in smokers. The defi nition of breastfeeding infants was also problematic in many studies. The e ffect of smoking on oxytocin in women was only examined in one study, and n o effect was found, yet a negative effect of smoking on oxytocin release is reported in the breastfeeding literature. Conclusion: Although there is co nsistent evidence that women who smoke breastfeed their infants for a short er duration than nonsmokers, the evidence for a physiological mechanism is not strong. (C) 200! Elsevier Science Ireland Ltd. All rights reserved.