The aim of this minireview was to summarize original data on the prevalence of alcohol intake during lactation, the influence of alcohol on breastfeeding, the pharmacokinetics of alcohol in lactating women and nursing infants and the effects of alcohol intake on the nursing infant.

Current recommendations by regulatory authorities (AUS, US, DK) and the American Academy of Pediatrics seem to be based on a ‘better safe than sorry’ approach and advise that women abstain completely from alcohol intake until they no longer breastfeed or at least avoid breastfeeding in the hours immediately after alcohol intake 3 , 7 - 9 . Various online resources that new mothers may consult similarly advocate abstention or delay before breastfeeding 10 , 11 . The Motherisk information service at the Hospital of Sick Children in Toronto, Canada, thus – very conservatively – recommends that breastfeeding women delay nursing their children until any ingested alcohol is completely eliminated from the milk or plan ahead by pumping out and storing milk before drinking 10 , and a nomogram has been developed in an effort to help the women calculate the length of this delay 12 .

The harmful effects of alcohol during pregnancy are well documented 1 and have led to very restrictive recommendations for pregnant women concerning alcohol intake 2 , 3 . However, the effects of alcohol during breastfeeding have not been nearly as extensively examined, and the literature on the prevalence of alcohol consumption during breastfeeding is scarce. Previously, it was a common belief that alcohol was beneficial during breastfeeding, and many women were encouraged to drink alcohol while lactating to relax, promote lactation and the milk ejection reflex and to enhance infant sleep 4 , 5 . This notion has somewhat subsided in recent years in favour of a more cautious approach, but versions of it still surface from time to time, which can cause confusion and concern in new mothers 6 .

Methods and Results

We searched PubMed from origin to May 2013 for the free‐text words ‘alcohol’ and (‘breastfeeding or lactation or human milk’). This resulted in 2090 hits, but after limiting the search to human studies reported in English, 946 remained. Of these, 39 studies were included for this minireview, while two additional references were identified from cross‐reference searches. A more specific search strategy, combining the MeSH terms ‘breastfeeding’, ‘lactation’ and ‘milk, human’ with the MeSH term ‘ethanol’, returned 27, 43 and 55 studies, respectively (using similar restrictions as above), all of which were included in the initial broader search. The included publications are summarized in online table S1.

The literature search and selection of included publications were performed in accordance with PRISMA guidelines 13. The selection tree is illustrated in fig. 1.

Figure 1 Open in figure viewer PowerPoint Flow chart of the selection of publications for inclusion in review.

Prevalence of alcohol intake during breastfeeding Eight studies published from 1990 to 2011 have reported prevalences of alcohol intake in lactating women ranging from 36 to 83%, with the highest prevalences seen in the oldest studies, see table 1 14-21. Table 1. Prevalence of alcohol intake during breastfeeding (*numbers from 1995 and 2001, respectively). Authors Country Publication year Methods No. of women surveyed Prevalence of alcohol intake during breastfeeding (%) Matheson et al. 14 Norway 1990 Questionnaire 885 83 Little et al. 15 USA 1990 Interview 220 66 Alvik et al. 20 Norway 2006 Questionnaire 1303 79.9 Parackal et al. 16 New Zealand 2007 Questionnaire 79 66 Breslow et al. 17 USA 2007 Questionnaire 772 35.9 Giglia & Binns 18 Australia 2007 Interview 287 46.7 Giglia & Binns 21 Australia 2008 Interview 1461/1248* 42.5/47.8 Maloney et al. 19 Australia 2011 Questionnaire and interview 807 43 Furthermore, in 1981, Davidson et al. 22 reported that only 38% of 261 participating women in Canada had received information about alcohol during breastfeeding. Ten percentage had been told to avoid alcohol, 45% that alcohol in moderate amounts was acceptable and 43% that alcohol was beneficial. Most of the women had received this information from healthcare professionals. More than half of the women who had avoided alcohol during pregnancy, consumed alcohol during breastfeeding, and 80% of the women who ingested alcohol during pregnancy, continued to do so while breastfeeding. In a similar study from 2004, Pepino and Mennella showed that of 167 Argentinian women surveyed, only about one in four had received information from healthcare professionals regarding alcohol intake during lactation. More than 44% reported that they were advised to drink a local alcohol‐containing drink, mate, to enhance their lactational performance. The majority had received this advice from family and friends, but 13% had heard it from their physician 23. Alvik et al. 20 showed that in Norway, 51% of the surveyed breastfeeding women ingested alcohol during the first 3 months after delivery, a number that rose to 80% after 3 months. Nearly all of these women reported a weekly intake of <7 standard drinks in the first 3 months, but after 6 months, approximately one in four women still breastfeeding engaged in binge drinking (>5 standard drinks per single occasion). Five percentage of these women had ingested 12 standard drinks on at least one occasion. Giglia et al. 21 reported that in Australia, more than 35% of the breastfeeding women who in the week before the study had ingested alcohol had consumed one or two standard drinks and that over 40% had consumed ≥5 standard drinks. From 1995 to 2001, the percentage of breastfeeding women who had consumed ≥10 standard drinks during the week before the study had increased slightly from 18 to 21%. More than 3% reported a daily alcohol consumption.

Alcohol's effect on breastfeeding Breastfeeding is controlled by the two pituitary hormones prolactin and oxytocin 24. Prolactin stimulates the production of breast milk, and oxytocin causes contraction of the smooth muscle cells surrounding the mammary tissue, thus causing ejection of the milk stored in the breast 24. Eight studies were identified concerning the effects of alcohol on breastfeeding 25-32. Contrary to previous beliefs of the beneficial effects of alcohol on breastfeeding, it has been demonstrated that alcohol to some extent inhibits lactation. One study of 22 lactating women, who were asked to express milk on two different days, one of which they had ingested 0.3 g alcohol per kg (corresponding to about 1.8 units of alcohol, assuming a body‐weight of 70 kg and an alcohol content of 12 g per unit), showed that the amount of milk expressed was 9.3% lower on average in the first two hours after alcohol consumption 25. It has also been demonstrated that alcohol dose‐dependently inhibits oxytocin and thereby the milk ejection reflex, which could probably explain this reduction in milk yield. However, the inhibitory effect of alcohol on oxytocin is subject to a sizeable interindividual variation 26, 27. Several studies have examined the inhibitory effects of alcohol on oxytocin levels. One such study found a 78% decrease in AUC for oxytocin after breast stimulation in women who had ingested 0.4 g alcohol per kg (or about 2.3 units of alcohol) and a corresponding increase in latency time to milk ejection. The milk yield was also reduced, and the prolactin levels were increased in the hours immediately after alcohol consumption (AUC for prolactin increased by 336 ± 222%) 28. Another study from Taiwan showed a 52% increase in latency time in women who ingested an alcohol‐containing soup as part of a cultural ritual 29. A more elaborate study of the pharmacokinetics of prolactin in relation to alcohol intake found that the basal prolactin levels were higher after alcohol intake than otherwise and that the effect of breast stimulation on prolactin levels were significantly altered by alcohol intake. If breast stimulation occurred during the time span where the alcohol concentration of the blood was increasing, breast stimulation caused significantly higher prolactin levels than if no alcohol had been consumed. If, however, breast stimulation occurred while the alcohol concentration was decreasing, the prolactin levels were statistically significantly lower 30. The clinical significance of these findings is not yet understood. Finally, it has been demonstrated that alcohol consumption affects the duration of lactation. Giglia et al. 31 showed that women who self‐reported a daily alcohol intake of >2 standard drinks were almost twice as likely to discontinue breastfeeding after 6 months than women who reported smaller consumptions. Similar findings were reported by Chaves et al. 32.

Pharmacokinetics of alcohol during lactation Twelve publications concerning the pharmacokinetics of alcohol during lactation were identified 5, 33-43. Alcohol passes freely into breast milk in approximately the same concentrations as in maternal blood; one study has shown marginally higher concentrations in blood 33, another in milk 34. The highest concentration is seen after 30–60 min, and the concentration declines linearly at the same rate as in maternal blood (i.e. approximately 15–20 mg/dL/h 1) due to dynamic equilibrium between plasma and breast milk 33-35. The toxic metabolite of alcohol and acetaldehyde is apparently not excreted into milk, even at high concentrations in maternal blood 33. Two studies have examined the pharmacokinetic profile of alcohol in lactating women 36, 37. Pepino et al. 36 compared 20 lactating women to nine formula‐feeding and 15 nulliparous women of similar age, weight, height and drinking habits. The study showed that the lactating women had statistically significantly lower maximum levels (C max ) and systemic availability (area under the curve, AUC) of alcohol in blood than the other two groups and that the time to maximum alcohol concentration (t max ) was the same for all groups. Da‐Silva et al. 37 found similar results in a small study of five lactating women and five age‐ and BMI‐matched controls who ingested 0.4 g alcohol per kg (or about 2.3 units). The lactating women had statistically significantly slower alcohol absorption (t max 48 versus 31 min.), lower AUC and lower alcohol levels in blood after 150 min. than the non‐lactating women. There are conflicting reports on the effect of lactation on the rate of elimination of alcohol. Some studies have not shown any effect 34, 37, whereas others have demonstrated a difference depending on the timing of nursing 38, 39. One of the latter studies examined the effects of breast stimulation with a breast pump in relation to alcohol intake and found a lower AUC and maximum blood alcohol concentration if breast stimulation was performed one hour prior to alcohol intake in contrast to 0.6 hr after. The rate of elimination was higher when breast stimulation was performed after alcohol intake. There was, however, no comparison group of non‐lactating women in this study 38. A subsequent study from the same authors found that breast stimulation affects the pharmacokinetics of alcohol even after cessation of lactation. Use of a breast pump 0.6 hr after alcohol consumption resulted in a longer t max and higher AUC after cessation of breastfeeding. In contrast, no such difference was found when the women had ingested alcohol one hour prior to breast stimulation 39. Studies have shown that a maternal alcohol intake of 0.3–0.6 g/kg (about 1.8–3.6 units) leads to a milk concentration of alcohol that would expose the nursing child to 0.0016–0.036 g/kg (i.e. approximately 5–6% of the weight‐adjusted maternal dose), if the child is breastfed at the time of maximum alcohol concentration in the milk 5, 33, 40. Theoretically, if a mother of 70 kg were to drink four standard drinks (of 12 g pure alcohol) at one occasion and then breastfeed her child at the time of the highest maternal alcohol concentration in blood (assuming complete absorption, a volume of distribution of 35 L and no metabolism of alcohol), the child would be exposed to 1.37 g/L in the breast milk. If the child then were to drink 150 mL milk (assuming a weight of 6 kg, a daily intake of 150 mL/kg over six feedings, and a total body water composition of 70% 41), the blood alcohol level of the child would be (0.15 L × 1.37 g/L)/(0.7 L/kg×6 kg) = 0.049 g/L, or 0.005% (about 1/10 the limit for driving legally in most European countries). The child is consequently exposed to only a fraction of the amount of alcohol ingested by the mother. Pikkarainen et al. 42 reported that the activity of alcohol dehydrogenase in newborns (up to 2 months of age) was approximately one‐fourth of the activity seen in adults. The clinical consequences of this difference were somewhat elucidated by Idänpään‐Heikkilä et al. who examined the rate of elimination of alcohol in mothers and infants. Six women in labour were given an alcohol infusion (8%, 6 mL/min.) until delivery (1.5–3.5 hr), at which point the alcohol levels in the umbilical cord blood were similar to those in maternal blood. During the first 4 hr, the elimination rate of alcohol in the newborns was 7.7 mg per 100 mL blood and 14.0 mg per 100 mL blood in the mothers. After 8 hr, the infants had almost twice as high alcohol blood levels as the mothers (11 ± 3 per 100 mL and 6 ± 2 per 100 mL, respectively) 43. Given that a nursing infant ingests such a small fraction of the maternal dose of alcohol, the approximately 50% lower rate of elimination in the child should have no clinical significance.

Alcohol's effect on the nursing infant Eleven studies on the effects of alcohol on the nursing infant were identified 5, 40, 44-52. Of these, three studies of a total of 36 participants have shown that children breastfed by women who had consumed alcohol prior to feeding ingested approximately 20% less milk in the first 4 hr after maternal alcohol consumption than otherwise 5, 40, 44. However, the children were breastfed more frequently and thus ingested larger amounts of milk 8–12 hr after maternal alcohol consumption, if the women did not consume any more alcohol 44. This reduction in the children's milk consumption is not caused by a dislike for the taste of the milk, but should probably be attributed to the reduced milk yield after alcohol intake. Mennella demonstrated that children ingest larger amounts of alcohol‐enriched milk than plain milk, when offered to them in a bottle 45. Small changes in the children's sleep patterns have been reported 5, 46, 47. Two studies have shown that the total amount of sleep was unchanged after intake of alcohol‐containing milk 5, 47, but that the sleep was divided into more, but shorter, intervals 5. The amount of active (REM) sleep was reduced for the first 3.5 hr in one study and then increased for the next 20.5 hr 47. In contrast to this, another study from the same group showed that the children's sleep on average was 25% shorter after ingesting alcohol‐containing milk and that the number of times the children slept was unchanged 46. The possible long‐term effects of alcohol in mother's milk are unknown. A single, frequently cited case from 1978 of an infant adversely affected by alcohol in the breast milk has been reported. The child was diagnosed with pseudo‐Cushing syndrome at 4 months of age, and upon examination, the mother reported a weekly intake of more than 17 L of beer in addition to other alcoholic beverages. The mother was encouraged to discontinue her alcohol intake, and afterwards, the child gradually reverted to a normal development 48. Little et al. 49 found an association between alcohol consumption during lactation and decreased psychomotor development. A total of 400 women, of which 153 reported a daily alcohol intake of two or more standard drinks and 243 reported less, were followed from before delivery until the children were 1 year old. The children of the women with the highest alcohol intake had statistically significantly lower scores on a scale of psychomotor development than the other children. Some of this differences could, however, be attributed to the fact that the mothers in this group were older or potentially other confounders. There was no difference between the children with regard to mental development, and the authors concluded that because any psychomotor development scale at 1 year is but a crude measure, the clinical importance of these findings was unclear. A later register‐based study from the same principal author could not reproduce the findings. The authors had information about maternal alcohol intake during lactation and subsequent motor evaluations of 915 children at 18 months of age and were unable to demonstrate any effects of alcohol consumption. However, there were more women who smoked, had a high alcohol intake or used marijuana in the original study 50. A Mexican study found no difference in rate of growth in children at 6 months of age when comparing the children of 32 women with a daily intake during pregnancy and lactation of 1–2 L of pulque (a fermented drink with 3% alcohol) with the children of 62 women without a daily alcohol intake 51. A later study, also from Mexico, of 58 mothers and children showed that the children of the women with the highest daily pulque intake during lactation had a statistically significantly poorer growth at 5 years of age, regardless of maternal pulque intake during pregnancy. The mothers in this group were, however, older than the 67 mothers in the control group who did not have a daily alcohol intake 52. The clinical interpretations of both of these studies are severely compromised by poor confounder control.