The present study confirmed previous findings (Mennella and Beauchamp, 1991
) that milk intake is diminished in the short term after exposure to alcohol in mothers’ milk. This reduction in milk intake was not due to infants feeding less because there was no significant difference in the number of breastfeeds that occurred during the 4 hr after alcohol exposure when compared with the control condition. The study also demonstrated, however, that infants then compensated for this reduction in milk intake when their mothers refrained from drinking any additional alcohol. This compensation appears to be due, in part, to the increased number of breastfeedings that occurred during the 8 to 12 hr post exposure. The findings were remarkably similar to those observed for the deficits in active sleep that also occur during the immediate hours after exposure to alcohol in mothers’ milk (Mennella and Garcia, unpublished; Mennella and Gerrish, 1998
). That is, previous research demonstrated that infants exhibited a 25% decrease in the amount of time spent in active sleep during the 3.5 hr after exposure (Mennella and Gerrish, 1998
). If mothers then refrained from drinking, the infants experienced an active sleep rebound during the next 20.5 hr (Mennella and Garcia, unpublished). Recall that the mothers in the present study also refrained from drinking alcohol during this time period. Whether similar findings would be observed if mothers continued to drink is unknown.
Infant feeding behaviors can be influenced by a variety of environmental and physiologic factors affecting both members of the mother-infant dyad. The present study aimed to experimentally control for a variety of such factors. For example, each of the test sessions occurred at the same time of day and testing occurred in a private, quiet room. The infants fed on demand and determined when the feed terminated. Moreover, mothers did not notice any difference in their infants’ behaviors or their experience of the let-down reflex. Although possible, it seems unlikely that the change in the patterning of breastfeeding was due to changes in the infants’ interaction with their mother. Rather, it appears that alcohol consumption by lactating mothers had an effect, albeit subtle, on the amount of milk consumed by their infants, which was due, in part, to a reduction in the amount of milk available to the infants (Mennella, 1998
Because the mothers in the present study drank very little during both pregnancy and lactation, we do not know whether infants who are frequently exposed to alcohol in mothers’ milk would experience growth deficits over the long term. However, the findings from two epidemiologic studies suggested that this might not be the case. One set of studies focused on nursing women living in central Mexico (Flores-Huerta et al., 1992
; Villalpando et al., 1993
). Folklore in this community relates that pulque, a low (3%) alcoholic beverage made from the fermented juice of Agave atrovirens
, is a galactagogue and women are encouraged to drink as much as 2 liters of this beverage daily during lactation. Although pulque can theoretically provide an additional energy load of 400–800 kcal to the women, there was no significant difference in their infants’ weight at 3 or 6 months when compared with the control infants of non-drinking, breastfeeding mothers.
The other study consisted of approximately 400 women who were members of a health maintenance organization in Seattle (Little et al., 1989
). Although women who breast fed were less likely to smoke cigarettes or marijuana or use cocaine, their “regular” drinking patterns at 1 and 3 months postpartum were not significantly different from those who had never breastfed their infants, although they were less likely to report occasional binges of heavy drinking. Approximately 10% of this sample of lactating women reported drinking two or more alcoholic beverages daily. Of interest here was the report that the weights, heights, and body mass indices of their infants at 1 year were not significantly different from similarly aged infants whose lactating mothers drank less (Little et al., 1989
). However, it is interesting to note that breastfeeding women who drank more heavily during lactation had higher nutrient intakes than those who did not (Little et al., 1994
To be sure, we do not know whether mothers who drink alcohol are more likely to complement their infants’ diets with solid foods at an earlier age. Nor do we know whether long-term alcohol consumption and perhaps alterations in nutrient intake (Little et al., 1994
) affect the caloric content of the milk. Animal model studies demonstrated that chronic
ethanol consumption during lactation resulted in significant reductions in milk yield (Vilaró et al., 1987
) as well as an altered fatty acid profile of individual phospholipids when compared with control dams (Heil et al., 1999
). Whether such effects were due to a direct consequence of prolonged drinking or malnutrition is not known. Nor do we know whether chronic alcohol consumption in humans has similar effects on the fatty acid profile of human milk.
Although the amount of alcohol ingested in breast milk is a minute fraction of that consumed by the mother (Mennella and Beauchamp, 1991
), the present study provides additional support for the hypothesis that acute alcohol exposure impacts upon the infants’ behaviors in the short term and raises serious doubts about the validity of the folklore that encourages women to drink during lactation. Perhaps one reason for the persistence of the folklore that occasional drinking by the nursing mother enhances breastfeeding (Falkner, 1987
; Fishman et al., 1988
; Flores-Huerta et al., 1992
; Grossman, 1987
; Krebs, 1953
; Walter, 1975
) is that the infants feed more later to compensate for the alcohol-induced deficits in their mothers’ milk production (Mennella, 1998
). The effects are subtle and remarkably similar to the changes in active sleep that follow exposure to alcohol in mothers’ milk (Mennella and Garcia, unpublished; Mennella and Gerrish, 1998
). These findings highlight the infants’ resiliency in modulating their behaviors in response to acute alcohol exposure and provide an obvious scope for future studies.