Bedsharing Promotes Breastfeeding

DISCUSSION

The most important finding of this study is that infants who bedshared routinely at home breastfed three times longer during the night than infants who routinely slept separately, when tested in their routine conditions. This largely reflected a two-fold increase in the number of breastfeeding episodes although the duration of individual episodes was, on average, also longer by 39%. These differences are only partly explained by acute or immediate effects of bedsharing because total breastfeeding time was significantly larger in the RB group than the RS group on the BN. This suggests that routine bedsharing promotes more nocturnal breastfeeding through additional factors not present during occasional bedsharing. Because diurnal breastfeeding was not measured in this study, we do not know if daytime feeding pattern is also affected by routine bedsharing at night. Available data on diurnal breastfeeding, however, provide no evidence that daytime feeding is diminished by breastfeeding at night.^7,27 Furthermore, how the results might be modified when a father or other family member is also present during bedsharing with the mother and infant is unknown.

Consistent with the laboratory findings, the sleep logs revealed that RB pairs were also breastfeeding more often than RS pairs at night at home. This indicates that the laboratory findings are, in general, representative of behavior in the natural environment. However, the number of breast feeds reported at home was approximately half that measured in the laboratory. Although this could reflect that infants actually fed more often in the laboratory, the more likely explanations are that mothers used a different criterion for defining a single feeding episode or that they underestimated the true frequency. Regarding the latter, there is other evidence that mothers underestimate the frequency of breastfeeding, compared with researcher observations.^8,9 Whatever the reason(s) for the discrepancy, it serves to emphasize the need for objective measures in quantifying breastfeeding behavior.

Although the mechanisms through which routine bedsharing promotes breastfeeding have yet to be determined, there is evidence that olfactory cues could be important. By 2 weeks of age, breastfed infants preferentially orient (by head turning) toward odors from their mother's breast and axillary regions during sleep as well as waking.^28,29 Consistent with some sort of sensory bridge between bedsharing infants and their mothers, we have found that bedsharing infants remain oriented toward their mothers for large portions of the night, up to 100%.³⁰ Inherent to bedsharing, the infant's proximity to the mother's breast would enhance the infant's exposure to olfactory and any other relevant sensory cues from the mother that might facilitate breastfeeding. One can further speculate that exposure to the mother's odors during bedsharing might have the effect of lowering the infant's arousal/hunger threshold. Bedsharing might also promote breastfeeding by permitting mothers to sense their infant's more subtle sounds and movements that increase in both frequency and intensity as breastfeeding episodes are approached (J. J. McKenna, unpublished observation, 1996). Because this kind of maternal responsiveness is not possible when infants sleep in a separate room, only by frank crying can the infant elicit maternal attention and feeding in the solitary condition.

That bedsharing promotes increased breastfeeding could have important implications for infant health. The most visible effect might be on weight gain (not measured in our study). Relatedly, Uvnas-Moberg et al³¹ reported that increased stimulation of the intraoral cavity of the newborn leads to an increased release of glucose and gastrointestinal food absorption hormones in newborns, and presumably in older infants too. In addition, Barr et al³² showed that more frequent infant feedings, especially those containing sugar nutrients (as opposed to water), reduce crying duration, thereby contributing to energy conservation and calm wakefulness presumably through both preabsorptive (orotactile and orogustatory) and postabsorptive mechanisms. Consistent with the latter, we observed that on the BN infants rarely cried to elicit a maternal response leading to a breastfeeding episode, whereas they almost always did so to elicit a feed on the SN (J. J. McKenna, unpublished observation, 1996).

An increased daily infusion of maternal antibodies at a time when their own immunological systems are least efficient may provide bedsharing/breastfeeding infants with increased protection from infectious diseases, some potentially related to SIDS. According to Arnon,³³ breastfeeding is important for protection against infant botulism that may be misdiagnosed as SIDS approximately 5% of the time. Bacterial infections also have been hypothesized by Blackwell et al³⁴ to interact with a range of infantile deficits to cause some SIDS deaths, and these too might be reduced by the increased breastfeeding associated with bedsharing. Arnon³³ suggests that the degree of protection from SIDS provided by mother's milk depends on the baby receiving greater amounts of secretory immunoglobulin A. If one assumes that longer total duration of breastfeeding equates with more milk intake, then the additional intake (however small) might help compensate for the natural variability of titers of antibodies that distinguish the content of one mother's milk from another's.³³

Two recent epidemiologic studies suggest that breastfeeding lowers the risks of SIDS,^14,15 and two others suggest that the extent of protection may be dose-related.^13,35 Whereas a protective effect has not been found in every study,²⁰ many international SIDS prevention campaigns, including in the United States, recommend breastfeeding as a way to reduce risk for SIDS. That bedsharing is associated with increased breastfeeding raises the possibility that bedsharing is a factor in the relatively lower rates of SIDS among the population from which our subjects were drawn. Our Latino mothers and infants represent a cultural group living in the Western and Southwestern United States for which their low socioeconomic and recent immigrant status suggest increased SIDS risk. Yet, similar to recent Asian immigrants in Great Britain,³⁶ the most recent epidemiologic data show that California Latino infants of Mexican-born mothers are at lower risk (.8/1000 live births) compared with Anglos (1/1000);³⁷ and for infants weighing more than 2500 g, this is also true among Latinos living in the Chicago area where the SIDS rates range from 1.0/1000 for Latino infants to 1.2/1000 for white middle-class infants.³⁸ That breastfeeding and bedsharing are more commonly practiced among recent Latino immigrants than in white American families may explain some of this discrepancy. Eighty-four percent of Mexican-born mothers in the United States initiate breastfeeding in contrast to 58.5% of white American mothers (Demographic and Health Surveys, 1991, unpublished data, Institute for Resource Development, Westinghouse Corporation).³⁹ Moreover, the incidence of all night bedsharing was found to be 21% among Latino families in east Harlem, New York City, significantly higher than the 6% reported for a representative sample of white, middle-class urban infants matched for age and sex.⁴⁰ That maternal smoking, a known risk factor for SIDS,⁴¹ may be relatively uncommon in Latino women may also be contributory. Furthermore, we found that bedsharing minimized use of the prone sleep position in our Latino subjects,³⁰which could also be a factor in the low SIDS rates reported for southern California Latinos because prone sleeping is a known risk factor for SIDS.⁴²

Although bedsharing is most often considered in terms of impact on infants, maternal reproductive physiology, particularly ability to reestablish ovulation, may also be affected. Suppression of ovulation contributes to increased iron status by delaying blood loss associated with menstruation and also extends the recuperative period between pregnancies, permitting the mother's body to replenish fat and nutrient stores required by herself as well as future offspring.^21,43 Recent studies suggest that frequent nipple contact or sucking and relatively short intervals between breast feeds (rather than simply breastfeeding versus not breastfeeding) are required to sustain the high levels of circulating prolactin which are known to suppress ovulation, increase birth interval, and thus limit maternal fecundity.^27,44 Although the complex interplay of behavior and physiology are yet to be deciphered, sucking duration was found to be important in prolonging lactational amenorrhea when sucking frequency is low, but less critical when sucking occurs 10 to 20 times per day and in which intervals between feeds are relatively short.⁴⁵ Although we do not know the pattern of our Latino mother's breastfeeding during the day, the more frequent nocturnal breast feeds, the shorter intervals between feeds and the longer total nightly durations occurring with routine bedsharing certainly reveal a nocturnal breastfeeding structure consistent with that known to suppress ovulation among women living in diverse cultural settings.^6,27,44 One can speculate that mothers who bedshare may be more likely to become pregnant later, rather than sooner, permitting their infants to benefit longer from less divided maternal attention and resource allocation,⁴⁶ thereby improving the mother's as well as the infant's prospects of better psychosocial and physical health.⁴⁷

In summary, these findings on nocturnal breastfeeding behavior are the first based on direct observation, instead of maternal recall, and the first to include the bedsharing environment. The discovery that bedsharing promotes breastfeeding has important implications both for infant and maternal health. Perhaps most important is that bedsharing might reduce the risk of SIDS because breastfeeding is thought to be protective against SIDS for some populations. However, given that bedsharing may increase SIDS risk when practiced in combination with maternal smoking,²³ the potential benefits of bedsharing cannot be considered independently of the specific social and physical circumstances within which bedsharing occurs. The potential for overlying or falling out of bed should be considered, in addition to the potential dangers associated with modern sleeping surfaces such as waterbeds, soft, fibrous, or bean mattresses, or loose bedding.^48,49 In older infants who continue to breastfeed, the possibility of promoting dental caries should also be considered.

Finally, our study has important implications for appreciating the potentially important effects that cultural choice of infant care practice has on the mother-infant relationship in general and on maternal and infant biology in particular. The differences we report between RB and RS mother-infant pairs underscore the need to reconceptualize normal mother-infant behavior, not in cultural terms alone, but also in biological terms. These findings reinforce the idea that mother and infant breastfeeding behaviors are highly sensitive to the environment within which they find expression and that expression is maximized when in the co-sleeping environment within which breastfeeding evolved.