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Open Access Publications from the University of California

Scholarly Works (14 results)

  • Article
  • Peer Reviewed
UC Santa Barbara Previously Published Works (2022)
In recent decades, Bolivia has expanded maternal and child health insurance coverage to improve access to prenatal and early life health care. Nationally, however, maternal and child health disparities persist along a rural-urban divide. Research is needed among rural populations to better understand local barriers to health care access and usage. Particularly among Indigenous populations, disparities may be compounded by differences in preferences for and access to traditional versus biomedical health care. We examined prenatal care and birth practices among Tsimane forager-farmers of El Beni, Bolivia. From 2012-2013, we interviewed 151 Tsimane mothers (0-35 months postpartum) from nine villages about birth and neonatal care practices, prenatal care, and pharmaceutical usage during labour and postpartum recovery. Results demonstrate local disparities in biomedical care usage by ease of access (e.g. proximity to market town, Spanish fluency), and maternal experience (e.g. parity and prior offspring death or miscarriage). While 59% of interviewed mothers had received at least one prenatal screening, services performed in screenings were limited. Nearly all women continue to birth at home with family assistance. Inconsistent access to health care services may be exacerbated by regional, generational, and educational disparities within the population.
    Cover page: Traditional and biomedical maternal and neonatal care practices in a rural Indigenous population of the Bolivian Amazon
    • Thesis
    • Peer Reviewed
    UC Santa Barbara Electronic Theses and Dissertations (2015)

    International health organizations recommend six months of exclusive breastfeeding (EBF) as optimal for infant health. Complementary feeding (CF) with any liquids or solids before this age risks increasing infant pathogen exposure and offsetting breast milk intake, which may increase risk of nutritional morbidity and early weaning. Globally, however, most infants begin CF well before six months—including in non-industrialized populations in which breastfeeding initiation and prolonged, on-demand nursing are universal. Why is early CF so common, even among populations in which prolonged EBF would be most protective for infants and feasible for mothers? Epidemiological research generally frames this discordance in terms of barriers to optimal practice and evolutionary research in terms of maternal-infant conflict—i.e. the benefits of reducing EBF costs for mothers may outweigh any risks for infants. An alternate and less-explored hypothesis is that early CF, if introduced without reducing breastfeeding intensity, may ultimately benefits infants.

    I examine evidence of maternal-infant conflict and congruence in shaping patterns of early CF among the Tsimane. The Tsimane are an indigenous, high-fertility, high-mortality, forager-horticulturalist population residing in the Bolivian Amazon. Interviews, anthropometric, behavioral, and biomarker data were collected from a mixed-longitudinal sample of Tsimane mother-infant pairs from August 2012 – April 2013. Tsimane mothers exhibited universal and prolonged breastfeeding, with EBF durations of about 4 months on average. Analysis of predictive factors and outcomes associated with age of CF introduction generally supported a Feeding Augmentation rather than a Feeding Substitution model of early CF. Mothers’ reasons for introducing CF more often emphasized perceptions of infant needs than their own time or energy constraints. Earlier CF introduction (0-3 vs. 4-6 months) was associated with increased CF frequency at later ages, but not with subsequently lower frequency of breastfeeding bouts or earlier weaning. Among mothers, shorter EBF durations were not associated with biological indicators of reduced lactational costs. While primiparity and high parity were both associated with age of CF introduction, these factors, and not age of CF introduction, were associated with timing of resumption of menstruation. Finally, while before six months of age infants who were introduced CF earlier were relatively smaller as compared to EBF counterparts, after six months of age mean height-for-age was higher for infants introduced CF at 0-3 vs. 4-6 months. Earlier CF was not associated with greater likelihood of reported illness before or after six months of age.

    Among the Tsimane early CF does not appear to benefit mothers at a cost to infants, and likely supplements, but does not supplant intensive breastfeeding. While the Feeding Augmentation Model was supported in this study, the Feeding Substitution Model may have more predictive power in populations in which bottle and formula feeding are more common. However, both models ultimately emphasize variability in optimal EBF duration, dually shaped by the needs of infants and mothers. This emphasis need not contradict current recommendations or related public health campaigns, but may be helpful in prompting a parallel dialog about optimal infant feeding practices for individual families

      Cover page: Optimal exclusive breastfeeding duration: evidence of conflict and congruence in Tsimane mother-infant pairs
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2013)
      Co-infection may affect transmission and recovery from infection, but remains an understudied element of disease ecology, particularly with regard to antagonism between parasites sharing a host. Helminth and giardia infections are often endemic in the same populations and both occupy the small intestine; yet few studies have examined interactions between these parasites. We report on helminth-giardia co-infections in a panel study of forager-horticulturalists in the Bolivian lowlands. Parasites were identified in faecal samples from 3275 participants, collected during 5235 medical exams over 6 years. Longitudinal co-infection patterns were examined using logistic mixed and multi-state Markov models. The most prevalent infections were hookworm (56%), Giardia lamblia (30%) and Ascaris lumbricoides (15%). Cross-sectionally, hookworm and A. lumbricoides were negatively associated with G. lamblia (OR = 0.60; OR = 0.65, respectively). Longitudinally, giardia infection was less likely in helminth-infected individuals (HR: 0.46). Infection with helminths was also less likely for individuals infected with giardia (HR: 0.71). Finally, treatment with mebendazole reduced subsequent hookworm infections, but resulted in a marginal increase in the odds of G. lamblia infection. Our results provide evidence for an antagonistic relationship between helminths and giardia, and suggest that co-infection should be considered in disease transmission models and treatment decisions.
        Cover page: Antagonism between two intestinal parasites in humans: the importance of co-infection for infection risk and recovery dynamics
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2017)
        Phthalates are a class of plasticizing chemicals produced in high volume and widely found in consumer products. Evidence suggests that phthalates may have non-monotonic effects on reproductive hormone activity. With exposure to phthalates virtually ubiquitous among industrialized populations, identifying unexposed and/or minimally exposed human populations is essential for understanding the effects of low level exposures. Our primary objective was to quantify urinary phthalate metabolite concentrations in the Tsimane', a remote population of Bolivian forager-horticulturalists. Our secondary objectives were to determine if phthalate metabolite concentrations vary in relation to access to market goods; and to explore relationships between phthalate and reproductive hormone metabolite concentrations. Given that phthalate exposure is of particular concern during fetal development, we focused on reproductive age women in the current analyses. Phthalate metabolites were assayed in urine samples from 59 naturally cycling, reproductive age Tsimane' women. Market access was assessed as: (1) distance from residence to the largest nearby town (San Borja, Bolivia) and (2) Spanish fluency. Urinary reproductive hormone metabolite concentrations were quantified using enzyme immunoassays. We fit linear models to examine: (1) predictors of phthalate exposure; and (2) relationships between urinary phthalate and reproductive hormone metabolite concentrations. Eight phthalate metabolites were detectable in at least 75% of samples. Median concentrations were up to an order of magnitude lower than industrialized populations. Proximity to San Borja and Spanish fluency were strong predictors of exposure. In exploratory analyses, the sum of the di-2-ethylhexyl phthalate metabolites (∑DEHP) and Mono-isobutyl phthalate (MiBP) were significantly associated with altered concentrations of urinary reproductive hormone metabolites. Remote, subsistence populations, like the Tsimane', offer a unique window into the health effects of endocrine active compounds because: (1) exposures are low and likely to be first generation; (2) a natural fertility lifestyle allows for exploration of reproductive effects; and (3) ever-increasing globalization will result in increasing exposure in the next decade.
          Cover page: Toxicoanthropology: Phthalate exposure in relation to market access in a remote forager-horticulturalist population
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2024)
          While the importance of human milk in shaping infant immune function is well established, the impact of at-the-nipple (ATN) breastfeeding on maternal immune status has been understudied. Since lactation evolved to support infant survival and boost maternal fitness, we predict that ATN breastfeeding will confer benefits on maternal immune function. We measure the absolute and relative frequency of different infant feeding methods (ATN breastfeeding, pumping, donated milk, other supplementation) used by postpartum women in Seattle, WA (USA). We implement Bayesian modeling to estimate the effects of ATN breastfeeding on diurnal change in secretion rate of pro-inflammatory salivary cytokines and C-reactive protein (CRP). Our results show that most mothers in our sample used a variety of infant feeding methods, with pumping as the most common alternative to ATN breastfeeding. We find that ATN breastfeeding is associated with non-linear effects on diurnal IL-8 and CRP. Furthermore, we find that women who report zero versus ubiquitous ATN breastfeeding exhibit opposing diurnal patterns in CRP secretion rate. This study provides evidence that variation in maternal lactation practices corresponds to differences in maternal immune responses, highlighting how measuring lactation as a continuous variable can further enhance understanding of postpartum maternal physiology.
            Cover page: Variation in maternal lactation practices associated with changes in diurnal maternal inflammation.
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2016)
            Six months of exclusive breastfeeding (EBF) is considered optimal for infant health, though globally most infants begin complementary feeding (CF) earlier-including among populations that practice prolonged breastfeeding. Two frameworks for understanding patterns of early CF emerge in the literature. In the first, maternal and infant needs trade-off, as "maternal-centric" factors-related to time and energy demands, reproductive investment, cultural influences, and structural barriers- favor supplanting breastfeeding with earlier and increased CF. A second framework considers that "infant-centric" factors-related to infant energetic needs-favor CF before six months to supplement breastfeeding. We apply these two frameworks in examining early CF among the Tsimane-a high-fertility, high-mortality, forager-horticulturalist population residing in the Bolivian Amazon. Data were collected from a mixed-longitudinal sample of 161 Tsimane mother-infant pairs from August 2012-April 2013. Tsimane mothers generally reported introducing CF because of perceived infant needs. However, CF is introduced with continued intensive breastfeeding, and generally coupled with premastication. Risks of earlier CF relative to the minimum hazard (estimated at 5 births) were elevated for lower and higher parity mothers, but were significantly greater only after 9 births. Seventeen percent of mothers reported introducing CF because of low milk supply. Introducing CF because of low milk was most common from 0 to 3 months of age and among higher parity mothers, which may reflect physiological constraints. Maternal reproductive trade-offs and perceived infant needs may help explain the low prevalence of EBF to six months among other populations in which breastfeeding is not structurally or culturally constrained.
              Cover page: Conflict or congruence? Maternal and infant-centric factors associated with shorter exclusive breastfeeding durations among the Tsimane
              • Article
              • Peer Reviewed
              Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 28 (2006)
                Cover page: Automated Team Discourse Modeling: Test of Performance and Generalization
                • Article
                • Peer Reviewed
                UC Santa Barbara Previously Published Works (2018)

                Background

                Traditional diets are often credited for the robust cardiometabolic health of subsistence populations. Yet, rural subsistence populations are undergoing nutrition transitions that have been linked to the increase in chronic noncommunicable diseases. Few studies have presented detailed dietary estimates in transitioning populations.

                Objectives

                We aimed to 1) characterize and compare dietary profiles of 2 neighboring subsistence populations in Bolivia who vary in market integration and 2) identify dietary factors contributing to low cardiovascular disease risk.

                Design

                We used a mixed longitudinal design to estimate nutrient intake via 24-h recall and dietary questionnaires among 1299 Tsimane (aged 30-91 y) and 229 Moseten (aged 30-84 y) men and women. We constructed population-level estimates of energy intake, dietary diversity, and nutrient shortfalls and analyzed dietary changes over time and space using multilevel models. Last, we compared Tsimane and Moseten dietary profiles with those of Americans (NHANES).

                Results

                The Tsimane diet was characterized by high energy (2422-2736 kcal/d), carbohydrate (376-423 g/d), and protein (119-139 g/d) intakes; low fat intake (40-46 g/d); and low dietary diversity relative to the average US diet. Most calories (64%) were derived from complex carbohydrates. Total energy and carbohydrate intake increased significantly during the 5-y study, particularly in villages near market towns. Tsimane consumption of food additives (lard, oil, sugar, salt) increased significantly [sugar (15.8 g ⋅ person-1 ⋅ d-1) and oil (4.9 mL ⋅ person-1 ⋅ d-1)] between 2010 and 2015. The more-acculturated Moseten consumed substantially more sugar (by 343%) and oil (by 535%) than the Tsimane.

                Conclusions

                A high-energy diet rich in complex carbohydrates is associated with low cardiovascular disease risk when coupled with a physically active lifestyle. A transition away from a high-fiber and low-fat, low-salt, and low-processed-sugar diet is a salient health risk for transitioning populations. Evidence of a nutrition transition in Bolivia parallels trends of increasing body fat and body mass index, which suggests that a low prevalence of cardiovascular disease may not persist.
                  Cover page: Nutrition transition in 2 lowland Bolivian subsistence populations
                  • Article
                  • Peer Reviewed
                  UC Santa Barbara Previously Published Works (2020)
                  Selective and neutral forces shape human microbiota assembly in early life. The Tsimane are an indigenous Bolivian population with infant care-associated behaviors predicted to increase mother-infant microbial dispersal. Here, we characterize microbial community assembly in 47 infant-mother pairs from six Tsimane villages, using 16S rRNA gene amplicon sequencing of longitudinal stool and tongue swab samples. We find that infant consumption of dairy products, vegetables, and chicha (a fermented drink inoculated with oral microbes) is associated with stool microbiota composition. In stool and tongue samples, microbes shared between mothers and infants are more abundant than non-shared microbes. Using a neutral model of community assembly, we find that neutral processes alone explain the prevalence of 79% of infant-colonizing microbes, but explain microbial prevalence less well in adults from river villages with more regular access to markets. Our results underscore the importance of neutral forces during microbiota assembly. Changing lifestyle factors may alter traditional modes of microbiota assembly by decreasing the role of neutral processes.
                    Cover page: Microbiota assembly, structure, and dynamics among Tsimane horticulturalists of the Bolivian Amazon
                    • Article
                    • Peer Reviewed
                    UC Santa Barbara Previously Published Works (2011)

                    Background

                    The peak shift model predicts that the age-profile of a pathogen's prevalence depends upon its transmission rate, peaking earlier in populations with higher transmission and declining as partial immunity is acquired. Helminth infections are associated with increased immunoglobulin E (IgE), which may convey partial immunity and influence the peak shift. Although studies have noted peak shifts in helminths, corresponding peak shifts in total IgE have not been investigated, nor has the age-patterning been carefully examined across populations. We test for differences in the age-patterning of IgE between two South American forager-horticulturalist populations and the United States: the Tsimane of Bolivia (n=832), the Shuar of Ecuador (n=289), and the U.S. NHANES (n=8,336). We then examine the relationship between total IgE and helminth prevalences in the Tsimane.

                    Methodology/principal findings

                    Total IgE levels were assessed in serum and dried blood spots and age-patterns examined with non-linear regression models. Tsimane had the highest IgE (geometric mean =8,182 IU/ml), followed by Shuar (1,252 IU/ml), and NHANES (52 IU/ml). Consistent with predictions, higher population IgE was associated with steeper increases at early ages and earlier peaks: Tsimane IgE peaked at 7 years, Shuar at 10 years, and NHANES at 17 years. For Tsimane, the age-pattern was compared with fecal helminth prevalences. Overall, 57% had detectable eggs or larva, with hookworm (45.4%) and Ascaris lumbricoides (19.9%) the most prevalent. The peak in total IgE occurred around the peak in A. lumbricoides, which was associated with higher IgE in children <10, but with lower IgE in adolescents.

                    Conclusions

                    The age-patterning suggests a peak shift in total IgE similar to that seen in helminth infections, particularly A. lumbricoides. This age-patterning may have implications for understanding the effects of helminths on other health outcomes, such as allergy, growth, and response to childhood vaccination.
                      Cover page: Evidence for a Peak Shift in a Humoral Response to Helminths: Age Profiles of IgE in the Shuar of Ecuador, the Tsimane of Bolivia, and the U.S. NHANES
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