Is Breast Best? Examining the effects of alcohol and cannabis use during lactation

1 Introduction

Breastfeeding is the optimal form of infant nutrition as breastmilk contains key nutrients such as fats, carbohydrates, protein, vitamins, and minerals [1]. Breastmilk also plays a vital role in strengthening infants’ underdeveloped immune systems, and in digestion and nutrient absorption [2]. In a prospective, longitudinal study of 107 healthy mother and infant pairs, 28% of the beneficial bacteria in an infant’s intestinal tract came directly from breastmilk and an additional 10% came from areolar skin, suggesting that bacteria in breastmilk seeds the infant gut [3]. In addition, the skin-to-skin contact that accompanies breastfeeding provides emotional bonding between mother and infant [1].

Infants should be exclusively breastfed during the first 6 months of life, since breastmilk provides all the necessary nutrients to the baby during this period. In 2011–2012, 26% of mothers in Canada exclusively breastfed for 6 months and this average increased from 2003 when the prevalence of exclusive breastfeeding was 17% [4]. Mothers who exclusively breastfeed for six months are more likely to be in their thirties and to have a post-secondary education. Of mothers who do not exclusively breastfeed, 44% felt they did not produce an adequate milk supply and 18% reported difficulties with their breastfeeding technique [4]. It has been suggested that low educated women may lack confidence in their ability to produce an adequate quality and quantity of breastmilk and this may cause them to breastfeed less [5]. Furthermore, low frequency and duration of breastfeeding could result in less milk being taken in by the infant, which then reduces the stimulation of milk production [1].

Despite the clear benefits of breastfeeding for infant nutrition, mothers need to be aware that what they consume can be passed to the baby through their breastmilk. Substances, for example, have been shown to pass into the breastmilk and alter milk production, volume, and composition [6]. Sachs et al. argue that mothers who continue to use substances during lactation should reconsider breastfeeding if they cannot abstain from its use [5]. Indeed, continued use of substances during breastfeeding can pose significant risks to the infant that may outweigh the benefits of breastfeeding [7]. Alcohol and other substances, such as cannabis and tobacco exhibit dose response effects, both during pregnancy and while breastfeeding [5, 8–11]; the higher the dose, the greater the likelihood of adverse effects to the infant, including toxicity, impaired motor development, reduced postnatal growth, decreased milk consumption, and sleep disturbances [6]. Given the extensive literature on tobacco use during lactation [12–22], the growing social acceptance of cannabis use [23, 24], and that alcohol and cannabis are commonly used substances among the breastfeeding population [25], the purpose of this review was to examine the risks associated with alcohol and cannabis use among breastfeeding mothers, and to make recommendations to healthcare professionals who work with these families.

2 Search strategy

The literature search was conducted using the following four databases: PubMed, CINAHL, Nursing and Allied Health, and Google Scholar. The search strategy was restricted to papers since the year 2000, and limited to English language journals. Search terms included: marijuana, cannabis, THC, alcohol, ethanol, breastfeeding, lactation, and breastmilk. The search results were evaluated by two authors by reading titles and abstracts. Papers evaluating the health effects of alcohol and/or cannabis use during the lactation period were included. Duplicate studies and research that was unrelated to our topic were excluded from this review.

The key findings of this review paper are presented in Tables 1 and 2. Table 1 provides information on the objectives, study design, location, sample size, and key findings for all articles pertaining to alcohol consumption and breastfeeding (n = 19). Table 2 provides the same information, but for cannabis use and breastfeeding (n = 4). Both tables included original research and systematic reviews that met our inclusion criteria, and excluded narrative reviews related to the topic.

Ethanol is a water-soluble, non-polar compound that has no plasma protein binding [6, 27]. This means that ethanol passes into human breastmilk similar to concentrations found in maternal blood due to ethanol’s solubility and molecular weight [25–27]. The metabolizing enzymes in the liver, which are a part of the substance elimination system, only reach 40% of the adult level by one month of age [6]. Due to this immature elimination system, substance clearance is low [6, 28].

A common misunderstanding is that alcohol elimination can be sped up by drinking water, resting, or by “pumping and dumping” [6, 28]. Pumping and dumping occurs when mothers pump their breastmilk within the two-hour period after consuming alcohol, and discard it before breastfeeding again [29]. Alcohol peaks in breastmilk within 30 to 60 minutes after consumption, paralleling maternal blood alcohol concentration (BAC) [6, 30–32]. Maternal BAC, in turn, varies by body weight, quantity of lean muscle mass and adipose tissue, stomach content at the time of alcohol consumption, and quantity of alcohol consumed [32]. In addition, because the rate of alcohol elimination is similar for both breastmilk and blood, alcohol in the breastmilk is eliminated through the mother’s blood [27]. Therefore, when maternal blood alcohol falls, so will the alcohol in breastmilk because it will be eliminated back into the blood supply [27].

The rate of alcohol consumption is increasing among women of childbearing age [25, 33]. In a recent cross-sectional, population-based Canadian study, Lange et al. found that 14% of women consumed alcohol while breastfeeding, and approximately 6% consumed alcohol during both pregnancy and breastfeeding [25]. Due to the nature of maternal under-reporting and social desirability, it is likely that the prevalence of alcohol consumption during breastfeeding is even higher [7, 34].

There is also a large body of research showing that high socioeconomic status is positively associated with alcohol consumption while breastfeeding [25, 35–38]. Lange et al. found that high educational attainment and income, being 35 years of age or older, smoking during pregnancy, and being married were associated with higher alcohol consumption during breastfeeding [25]. Similarly, Giglia et al. found that women who consumed alcohol during breastfeeding were more likely to have high incomes and to have attended antenatal classes [35]. Maloney et al. concluded that older age and higher educational attainment were significantly associated with alcohol use while breastfeeding [37]. A systematic review concluded that high levels of income and education were characteristics of mothers that drank during lactation.

There is limited knowledge about the potential negative effects of maternal alcohol consumption while breastfeeding [25, 34]. Common misconceptions surround alcohol consumption and improved infant sleep quality, increased quality and quantity of breastmilk, and its aid in the letdown reflex [27, 39]. A systematic review, for example, found that even small quantities of alcohol can negatively affect infant sleep quality by significantly reducing the time spent in active sleep immediately after exposure to alcohol in breastmilk [27].

Research has also found that alcohol affects the initiation and duration of breastfeeding by inhibiting the role of oxytocin [1, 41]. Oxytocin is one of two hormones directly responsible for milk release in response to the suckling infant on the breast [1, 42]. This promotes the milk ejection reflux, which in turn empties the breast [32]. Alcohol inhibits the release of this hormone, resulting in an overall reduction in oxytocin, which subsequently hinders the let-down reflex and milk yield [26, 32]. Doses as low as 0.3 g/kg body weight have been shown to have an inhibitory effect on oxytocin, with ensuing decreases in milk intake [27]. As well, infants consume 20% less breastmilk during the 4 hours immediately after alcohol exposure due to a reduction in the milk produced [43]. High levels of alcohol consumption during lactation contribute to the early cessation of breastfeeding [27, 35], although low levels appear to have little impact on breastfeeding duration [38]. In their review, Haastrup et al. argue that the body of original research surrounding alcohol and lactation is limited and that existing research is primarily conducted by a core group of researchers, which may result in recruitment bias and compromise the ability to generalize these data to a greater population [44].

Public health efforts that have raised awareness against alcohol consumption during pregnancy have contributed to significant decreases in alcohol consumption during this period [25]. However, women who abstain from alcohol while pregnant tend to revert to their pre-pregnancy drinking behaviors once their babies are born, regardless of whether they breastfeed [25, 45]. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recommend avoiding heavy alcohol consumption and binge drinking during lactation, and advise that nursing be delayed for two hours after alcohol consumption to reduce infant exposure [46]. The Motherisk team at Hospital for Sick Children (SickKids) in Toronto is an evidence-based teratogen information service for women, their partners and healthcare professionals [47]. This service provides current information on the risks and safety of medications and other exposures during pregnancy and breastfeeding [47]. The Motherisk program endorses complete alcohol clearance from the breastmilk before breastfeeding, and advises mothers to follow a breastfeeding schedule when they consume alcohol [28]. The Motherisk team has also designed a nomogram, based on pharma-kinetic modeling, which considers the weight of the mother and quantity of alcohol consumed. This was designed to help mothers, along with their healthcare providers, determine the time that it takes for alcohol to be eliminated from the breastmilk [28]. Assuming an average maximal elimination rate of 15 mg/dL/hr and approximately 17 g of alcohol per standard drink, mothers should wait 2–3 hours before breastfeeding to ensure that the alcohol has been eliminated from their breastmilk [48]. The World Health Organization (WHO) maintains that women should continue to breastfeed even if they have the occasional drink of alcohol, although it is best to restrict or abstain from alcohol completely [42].

4 Cannabis

According to Statistics Canada, 11% of Canadians aged 15 years or older used cannabis in 2013 [49]. This number is expected to increase due to growing social acceptance and the recent legalization of medicinal and recreational cannabis in certain states in the U.S., and the plans to legalize cannabis in Canada [50–53].

Cannabis is also the most commonly used illicit drug during pregnancy [54], and mothers are likely to continue its use while breastfeeding [55]. In a convenience sample of 74 lactation professionals, 15% (1,203/7,843) of their breastfeeding clients used cannabis in the past 12 months; 41% of lactation professionals urged women to continue breastfeeding while using cannabis; 44% indicated that their recommendation would depend on several factors (e.g., the quantity of cannabis used); and 15% recommended abstaining from breastfeeding completely [56].

Due to limited and inconsistent evidence about the effects of cannabis use during breastfeeding, it is difficult to establish concise recommendations and guidelines for breastfeeding mothers [55–57]. Although some studies report that the benefits of breastfeeding outweigh the risk of cannabis use [30, 54], other studies report that breastfeeding and cannabis use is contraindicated [26, 58–63]. To date, only two systematic reviews have evaluated the effects of cannabis use during lactation [57, 63]. Ordean [57] concluded that the effects of cannabis exposure during breastfeeding remain unclear, and that women should continue to be consulted on the benefits of breastfeeding and the harmful effects of cannabis use. Conversely, Seabrook et al., [63] maintain that mothers who breastfeed should not be recommended medicinal cannabis due to the risks associated with poor neurobehavioral outcomes, and that breastfeeding mothers should be advised to reduce or cease their cannabis use completely.

Delta-9-tetrahydrocannabinol (THC) is the psychoactive compound in cannabis [62] and has a small molecular size, allowing it to transfer into breastmilk and concentrate there [26, 62]. Due to the chemical structure of THC, it can enter the bloodstream within seconds after inhalation and pass into the brain cells within minutes. Analysis of the breastmilk of mothers who use cannabis shows that THC is bound to proteins available in breastmilk [54]. Studies suggest that in one feeding, infants can ingest about 0.8% of the quantity of cannabis consumed by the mother [54, 64]. In some cases, milk THC concentrations can be eight times more than the concentration in maternal plasma [62]. THC is absorbed in the gastrointestinal tract of infants and is subsequently metabolized and excreted. This has been observed through fecal analysis and THC metabolites that have been found in the feces of infants [30, 55].

Although there have been limited studies on the effects of cannabis use during breastfeeding, associations have been found with infant sedation, reduced muscular tonus, poor sucking, growth delay and restriction [24, 65], tremors, decreased feeding time, and changes in visual responses [66]. Animal research has shown that cannabis exposure alters DNA, and impairs the proteins needed for growth and development of brain cells [58].

Cannabis use during the lactation period also affects the quality and quantity of milk produced [24, 66]. Human and animal studies show that THC inhibits the production of prolactin [67], the hormone associated with breastmilk production, which directly affects the quantity of milk produced. Furthermore, THC inhibits the release of gonadotropin, growth hormone (GH) and thyroid stimulating hormone (TSH), while stimulating the release of corticotropin [55]. Taken together, these hormones affect the quality of milk produced.

Mixed results have been found with regards to cannabis exposure and infant IQ. Wang [68] found that cannabis exposure lowers IQ, whereas Hill and Reed [54] argue that IQ is not affected by cannabis exposure, although school-aged children who were breastfed by cannabis-using mothers were less attentive and more impulsive at school. Definitive conclusions about the attentiveness and impulsivity of children are challenging, however, because they may be confounded by social determinants of health and other substance abuse [54].

In addition to the child health outcomes associated with maternal cannabis use, cannabis consumption has negative health effects on the breastfeeding mother. Mothers who use cannabis during lactation are at higher risk for depression and schizophrenia postpartum compared to non-users [55, 58]. Cannabis consumption during lactation is also associated with a higher risk of panic attacks [58, 66], delayed response time [58, 66], increased heart rate [58, 66], reduced short-term memory [64], dizziness, and impaired motor performance [64]. These negative health outcomes may in turn compromise a mother’s ability to nurse and care for her infant.

Lastly, there are several challenges with assessing the impact of cannabis exposure on child health outcomes during lactation. First, most studies only examine the effects of prenatal cannabis use, with very few assessing postnatal exposure [30, 69]. As well, over 80% of women who use cannabis during pregnancy continue using it during lactation [24], thus potentially confounding the impact of postnatal exposure on child health outcomes. Second, cannabis use is subject to under-reporting since many women are worried about the legal consequences of its use and the risk of child protective services being contacted [30, 55]. Third, studies examining the effects of cannabis use during the perinatal period tend to be confounded by a poly-drug effect, such that cannabis users are also more likely to use alcohol and tobacco, which makes it difficult to estimate the independent effects of one particular drug [30, 62]. However, a recent Canadian study of 26,654 live births found that, after adjusting for alcohol and tobacco use, and socioeconomic status and previous medical history, women who used cannabis during pregnancy had an almost three-fold higher odds of having a low birth weight baby than women who did not use cannabis [70].

5 Conclusions and recommendations

The key point to take from this review is that recommendations about substance use and breastfeeding really depend on quantity consumed. While abstaining from substance use is always more ideal for infant outcomes, women should continue breastfeeding if they choose to have an occasional drink of alcohol. This recommendation coincides with that reported by the WHO [42]. However, like recommendations posed by SOGC [46], healthcare providers should inform breastfeeding mothers to avoid heavy alcohol consumption and binge drinking. It is also noteworthy that because no acceptable level of alcohol in breastmilk has been established, healthcare professionals should be cautious informing breastfeeding mothers that any quantity of alcohol consumed is safe.

Like alcohol, there is no safe limit of cannabis consumption during lactation. However, the potency of THC has increased by 300% , from 3% in the 1980s to 12% in 2012 [23]. With this increase in potency, breastfeeding mothers should be recommended to limit or cease their use of cannabis entirely. If mothers continue using cannabis during lactation, they should do so in an environment away from their children to reduce second-hand exposure. Like tobacco smoke, exhalation of cannabis smoke increases the risk of respiratory illnesses in infants, including asthma, bronchitis, and pneumonia [71]. Mothers should also change their clothes after smoking so their children do not get exposed to smoke particles, similar to recommendations for tobacco smoking mothers [54]. If cannabis consumption is heavy, defined in one study as mothers smoking≥5 joints per day [72], and this quantity cannot be reduced, mothers should be advised to cease breastfeeding and exclusively formula-feed their baby.