Ruta Nonacs, MD, PhD

The harmful effects of alcohol use during pregnancy are well-established.

 We know much less, however, about the consequences of alcohol intake in breastfeeding women and their infants. In the clinic when we review a patient’s medical history, we regularly query women about their use of tobacco, alcohol, and other substances, and we advise women regarding the deleterious effects of these substances when taken during pregnancy. 

There seems, however, to be considerable variation in what is recommended for breastfeeding women. With regard to the consumption of alcohol by breastfeeding women, some health care providers urge abstinence, while others state that alcohol consumption by breastfeeding women carries little risk.

In a recent review, Haastrup and colleagues reported that the prevalence of alcohol consumption in breastfeeding women is high, ranging from
	36% to 83% in developed countries.

 Epidemiological studies have shown that while breastfeeding women were less likely to report binge drinking, patterns of drinking at 1 and 3 months after giving birth did not differ significantly between women who chose to breastfeed and women who never breastfed.

Although information regarding the effects of alcohol consumption on breastfeeding women and their infants is limited, it is essential that women receive accurate information regarding the potential risks of exposure to alcohol transferred to the infant as a result of breastfeeding. 

PK and metabolism of alcohol in mother and infant

Alcohol consumed by a mother passes freely into her breast milk; alcohol levels in breast milk are similar to those measured in maternal blood and peak 30 to 60 minutes after an alcoholic beverage is consumed.

 The amount of alcohol taken in by a nursing infant through breast milk is estimated to be 5% to 6% of the weight-adjusted maternal dose.

Alcohol can typically be detected in breast milk for about 2 to 3 hours after a single drink is consumed. However, it must be noted that the length of time alcohol can be detected in breast milk increases according to the amount of alcohol a mother consumes. Alcohol from 1 drink can be detected in breast milk for about 2 to 3 hours but the time period extends to about 4 to 5 hours if a mother consumes 2 drinks and to about 6 to 8 hours if she consumes 3 drinks, and so forth. Other factors influencing the amount of alcohol in breast milk include how fast it is consumed, whether it is consumed with food, the mother’s body weight, and individual variations in alcohol absorption and metabolism.

Blood alcohol levels in a nursing infant depend on the amount of alcohol in breast milk, but also on the infant’s capacity to metabolize alcohol. In a newborn, alcohol is metabolized at 25% to 50% of the rate observed in adults.

Breastfeeding women are sometimes told they should drink alcohol to boost breast milk production and that the nutrients contained in dark stout beers, like Guinness, help to nourish the baby. In the early 1900s, beer companies marketed low-alcohol beers or “tonics” specifically for nursing women as a means of increasing their strength and enhancing breast milk production.

Like many old wives’ tales, there is a grain of truth to these recommendations. The barley used to make beer contains a polysaccharide that increases prolactin production, which in turn stimulates breast milk production.

 However, alcohol on its own actually decreases milk production.

Alcohol also is a potent inhibitor of oxytocin. Because of this effect, it was used clinically in the 1970s to stop contractions and prevent preterm birth. In a nursing mother, however, release of oxytocin associated with ingestion of alcohol stimulates milk ejection, which may also decrease the amount of milk available to the nursing infant.

 The higher the alcohol intake, the greater the effect; however, one study noted that drinking as little as 0.3 g of alcohol per kg (which is less than the amount considered acceptable by the American Academy of Pediatrics) reduced milk production by about 10%.

Short-term effects of alcohol on a nursing infant

Studies have shown that infants breastfed by women who had consumed alcohol prior to nursing consumed approximately 20% less milk in the first 4 hours after maternal alcohol consumption than women who did not drink.

 However, a subsequent study reported that, if mothers did not consume any more alcohol, babies breastfed more frequently and consumed larger amounts of milk in the 8 to 12 hours after maternal alcohol consumption.

Although some have speculated that this reduction in infant milk consumption may be caused by changes in the taste of the milk, it is probably more related to decreased supply. In fact, Mennella observed that infants actually consumed larger amounts of alcohol-enriched milk than plain breast milk, when provided to them in a bottle.

Changes in infants’ sleep patterns have also been observed.

While 2 studies reported that the total amount of sleep was unchanged after consuming alcohol-containing milk, these studies noted that the sleep was more fragmented.

 In contrast, another study demonstrated that total duration of sleep decreased on average by about 25% after infants consumed alcohol-containing milk.

Long-term effects of alcohol on a nursing infant

Possible long-term effects on infants of alcohol delivered in mother’s milk are less studied, with only a handful of the studies looking at neurodevelopmental outcomes in exposed infants. However, this may be a particularly difficult area of research. Not only must we consider the direct effects related to alcohol exposure via breast milk, it is possible that alcohol consumed by the mother may have an effect on a developing child by altering the mother’s behavior or her capacity to parent. 

In a study of 400 infants, Little and colleagues investigated infant development at age 1 year in relation to maternal use of alcohol while breastfeeding.

 Cognitive development, as measured using the Bayley Mental Development Index (MDI), was not affected by maternal use of alcohol. However, indices of motor development, as measured using the Psychomotor Development Index (PDI), were significantly lower in infants exposed regularly to alcohol in breast milk (even after controlling for prenatal alcohol exposure). The researchers observed an inverse dose-response relationship between the frequency of maternal alcohol consumption and scores on the PDI. Infants of breastfeeding mothers who had 1 or more drinks daily had a mean PDI score of 98, compared to a mean score of 103 in infants exposed to less alcohol in breast milk (95% confidence interval of the mean difference, 1.2 to 9.8). This association persisted after controlling for more than 100 potential confounding variables, including smoking and use of other drugs. In addition, the effect was more pronounced when mothers who supplemented breastfeeding with formula were excluded from the analysis. 

However, in a similar study from the same group, there was no association between scores on the Griffiths Developmental Scales and alcohol exposure in a group of 18-month-old children.

 The researchers note that, while the Bayley and Griffith Scales are comparable in terms of their ability to detect neurodevelopmental deficits, these tests, when used in infants and toddlers, are limited in their ability to detect small effects. They suggest that studies of older children may be of greater utility in assessing the effects of drinking while nursing.

More recently, data were analyzed from Growing Up in Australia: The Longitudinal Study of Australian Children, which included 5107 Australian infants and their caregivers recruited in 2004.

 Information on breastfeeding, alcohol use, and other demographic variables were collected at baseline, and the children were assessed every 2 years. Heavier maternal alcohol consumption at the initial assessment was associated with dose-dependent reductions in abstract reasoning at ages 6 to 7 years in children who had been breastfed. This association was not observed in infants who had never breastfed, suggesting that exposure to alcohol via breastmilk, rather than psychosocial or environmental factors associated with that exposure, was responsible for the reductions in cognitive functioning observed in breastfed infants. This finding was independent of prenatal alcohol use, sex of child, maternal age, income, birth weight, and breastfeeding duration. Smoking while breastfeeding did not impact any of the outcomes studied.

While these studies raise concerns about the impact of alcohol on a nursing infant, there are many different patterns of alcohol consumption, and it would be erroneous to assume that having an occasional drink carries the same risk as chronic, heavy drinking or binge drinking. Our understanding of the impact of alcohol consumption is made even more complicated by the fact that there are genetic, psychosocial, cultural, and economic factors that go along with and influence alcohol consumption; these factors may also significantly impact children’s outcomes. 

All pregnant and postpartum women should be queried regarding their past and present use of alcohol. National surveys indicate that about 1 in 2 women aged 18 to 44 drink alcohol, and 18% of women who drink alcohol in this age group binge drink. While many women with alcohol use disorders are able to abstain from drinking during pregnancy, relapse rates are high after delivery.

 In addressing maternal use of alcohol, screening for problematic patterns of use and offering treatment when appropriate may help to reduce behaviors that put an infant at risk. 

Proximate to delivery, all women should be provided information regarding use of alcohol while breastfeeding. Although the information is incomplete, our current data indicate that maternal alcohol consumption may affect milk production and infant sleep patterns. In addition, the most current studies indicate that alcohol passed through breast milk may have adverse neurodevelopmental effects.  

Guidelines regarding use of alcohol are varied. According to the most recent recommendations on breastfeeding from the AAP,

 “ingestion of alcoholic beverages should be minimized and limited to an occasional intake but no more than 0.5 g alcohol per kg body weight, which for a 60 kg mother is approximately 2 oz liquor, 8 oz wine, or 2 beers.” Furthermore, they recommend that mothers avoid nursing their infants for 2 hours after their last drink to allow for the alcohol to be cleared from the breast milk. 

The Motherisk program in Toronto, Canada, has issued more conservative recommendations,

“At this time, there are no known benefits of exposing nursing infants to alcohol. Although occasional drinking while nursing has not been associated with overt harm to infants, the possibility of adverse effects has not been ruled out. Occasional drinking, however, does not warrant discontinuing breastfeeding, as the benefits of breastfeeding are extensive and well recognized. Until a safe level of alcohol in breast milk is established, no alcohol in breast milk is safest for nursing babies. It is, therefore, prudent for mothers to delay breastfeeding their babies until alcohol is completely cleared from their breast milk.”

To minimize exposure, Motherisk has developed a nomogram that can be used to help mothers who choose to drink alcohol while breastfeeding estimate how long it takes to clear alcohol from breast milk, taking into consideration body weight and number of drinks (Table 1). 

Information about the long-term effects of exposure to alcohol during breastfeeding remains lacking. Therefore, to minimize the risk of adverse events in nursing children, it is best to counsel mothers on adhering to recommendations from healthcare authorities on alcohol intake in breastfeeding women

The author reports no potential conflicts of interest with regard to this article.

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