Comparative study of breastfeeding structure and its relation to human reproductive ecology

Abstract

Although a controversial issue in the not distant past, it is now well established that breastfeeding is the primary factor mediating post-partum subfecundity. This complex interaction between behavior and physiology is a central research focus in several fields sharing a common concern with the mechanisms that regulate human reproduction. Despite the demonstrated linkage between lactation and return of the first postpartum menses, many questions regarding the relationship between variation in breastfeeding behavior and variation in ovarian function remain unanswered. In particular, women of seemingly comparable breastfeeding magnitude display substantial heterogeneity in the duration of post-partum subfecundity. In addition, the hormonal mechanisms by which lactation regulates ovarian function remain unclear, and the debates regarding the contribution of factors other than breastfeeding to post-partum subfecundity continue unresolved. Part of the difficulty in addressing these questions derives from the use of disparate methodological approaches and a n absence of specificity in analytical units. In particular, maternal recall of breastfeeding behavior is subject to substantial bias yet is the data source for most analyses. In addition, although a growing body of evidence suggests that variation in breastfeeding structure may contribute to variation in ovarian function, most studies fail to distinguish or evaluate the different components of suckling behavior. Elucidating the bases of this variation amongst women and populations requires disentangling the roles of the environment, culture, and behavior in structuring suckling activity. Anthropologists in particular have a n opportunity to achieve significant insights into the ecology of human breastfeeding and reproduction. An impressive body of research has firmly established that breastfeeding is the major determinant of post-partum amenorrhea (e.g., Perez et al., 1971;Berman et al., 1972;van Ginneken, 1977;Wenlock, 1977;Konner and Worthman, 1980;Jain and Bongaarts, 1981;Bracher and Santow, 1982;Howie and McNeilly, 1982;Hennart et al., 1985;Rivera et al., 1985;Diaz, 1989;Glasier, 1989;Gray et al., 1990). These investigations were initially prompted by the hypothesis that variation in lactation might contribute to fertility differences among populations (Gioiosa, 1955;Henry, 1961;Tietze, 1961), a suggestion contrary to the then prevailing biomedical position, which dismissed any purported effects of nursing on conception.0 1994 Wiley-Liss, Inc. [Vol. 37, 1994 Investigations of lactation now occupy a central position in the study of human fecundity and fertility in several fields. Ecologists seek to understand how the human reproductive system has evolved and how women partition energy to the competing demands of production and reproduction. Of particular interest is the selective advantage that may exist in delaying effort in the production of more offspring (Frisch, 1978;Quandt, 1984;Blurton Jones, 1986;Ellison, 1990Ellison, , 1991Peacock, 1990 Pea...

Correlates of breastfeeding frequency among nomadic pastoralists of Turkana, Kenya: A retrospective study

“…Suckling activity was not clustered into well-defined sessions (a series of closely spaced episodes), as had been observed by Vitzthum among Quechua women (1989), but occurred instead as a series of isolated episodes, usually lasting no more than 2 or 3 min but separated by intervals longer than l min (for a nice illustration of this pattern, see Fig. 1 in Vitzthum, 1994a). The frequency of suckling increased dramatically as children approached the second half of their second year.…”

“…Although effects on fertility of the duration of lactation have been known for some time (see Bongaarts, 1981), only recently have scientists begun to understand the impact of daily breastfeeding structure (McNeilly et al, 1988). It is now clear that this structure varies markedly among so-called natural fertility populations (Campbell and Wood, 1988), with important consequences for population differences in the timing of the resumption of menses postpartum and of the length of interbirth intervals (Gray, 1994a;Vitzthum, 1994a).…”

Life history theory and the immune system: Steps toward a human ecological immunology

“…The now well-established area of reproductive ecology (building on biomedical research in endocrinology) has repeatedly demonstrated how such a framework can lead to insights at conceptual and physiological levels (Campbell and Wood, 1994;Ellison, 2001;Konner and Worthman, 1980;Vitzthum, 1994;Wood, 1994). The time has come for similar efforts in field-based, populationlevel research in immunology.…”

Reconstruction of breastfeeding and weaning practices using stable isotope and trace element analyses: A review

“…Furthermore, there are great individual variations in BWPs in modern traditional and industrialized human populations (Vitzthum, 1994). Individual variations in BWP cannot be discussed in most cross-sectional reconstructions, but can be in longitudinal reconstructions using isotopic signals in hair (Fuller et al, 2006a), serial sections of tooth dentin (Eerkens et al, 2011;Beaumont et al, 2013b;Eerkens and Bartelink, 2013;Henderson et al, 2014), and elemental signals in thin-sectioned tooth enamel (Humphrey et al, 2008a;Austin et al, 2013).…”