Breastfeeding durations relate to maternal body size and infant care help across 21 small-scale human populations: Implications for public health

摘要

Research question: The duration for which infants are exclusively breastfed (exBF) and the total duration for which infants are breastfed (exBF plus supplemented breastfeeding or TBF) influence numerous health outcomes over the lifecourse. In particular, a growing body of epidemiological evidence indicates that shorter durations of exBF and TBF are associated with increased risks of developing obesity-related non-communicable diseases such as diabetes and heart disease in adulthood, making the promotion of appropriate exBF and TBF durations a public health priority. The available evidence, derived almost entirely from industrialized, state-level populations with strong socio-cultural stigmas against overweight and obesity, indicates that bigger mothers are less likely to breastfeed at all and are likely to end exBF and TBF earlier, compared to other mothers. It is currently unclear whether this is a general human pattern with a physiological explanation or whether it is unique to industrialized populations in which overweight and obese mothers breastfeed less for cultural reasons (e.g. stigma-tization, lack of body confidence, lack of help with infant care). Methods: With this in mind, we used published data from anthropological literature to investigate whether population mean durations of exBF and TBF are associated with coarse indicators of maternal adiposity and amount of help with infant care across a sample of 21 small-scale human populations from 16 countries on four continents; adult female adiposity is not stigmatized and is even viewed as desirable in most of these populations. Our adiposity indicator was population's mean adult female Body Mass Index (BMI; weight/height ). Our infant care help indicator was a dummy score of whether or not mothers in a given population were generally reported to be holding their infants at least 65% of the time during infants' first year of life. We fit linear mixed models by maximum likelihood to the data, allowing intercepts to vary randomly among continents. Results: We found that population's mean duration of exBF was longer in populations in which mothers received relatively little help with infant care; exBF duration was not associated with population's mean adult female BMI. In contrast, population's mean duration of TBF was not associated with amount of help mothers received but was significantly negatively associated with population's mean adult female BMI. Specifically, each one-point increase in BMI was associated with approximately 1.6 months reduction in TBF duration. Conclusions: Our results suggest that the negative association between duration of exBF and maternal adiposity reported in epidemiological studies may be socio-culturally driven and unique to industrialized, state-level populations. They further suggest that the previously documented negative association between TBF duration and maternal body size likely reflects a more general human pattern. These findings imply that promotion of extended exBF duration should perhaps focus on cultural factors (e.g. reducing stigma, improving self-efficacy and body confidence for bigger mothers in industrialized populations; considering the role of infant care structure in small-scale populations). Promoting longer durations of TBF may require deep understandings of the physiological tradeoffs it involves for mothers of all sizes and in a wide variety of contexts.