Epigenetic mechanisms underlying the association between maternal climate stress and child growth: characterizing severe drought and its impact on a Kenyan community engaging in a climate change-sensitive livelihood

Pastoralists in East Africa are among the world's most vulnerable communities to climate change, already living near their upper thermal limits and engaging in a climate-sensitive livelihood in a climate change global hot spot. Pregnant women and children are even more at risk. Here, we report the findings of a study characterizing Samburu pastoralist women's experiences of severe drought and outcomes in their children (N = 213, 1.8-9.6 y). First, we examined potential DNA methylation (DNAm) differences between children exposed to severe drought in utero and same-sex unexposed siblings. Next, we performed a high-dimensional mediation analysis to test whether DNAm mediated associations of exposure to severe drought with body weight and adiposity. DNAm was measured using the Infinium MethylationEPIC BeadChip array. After quality control; batch, chip, and genomic inflation corrections; covariate adjustment; and multiple testing correction, 16 CpG sites were differentially methylated between exposed and unexposed children, predominantly in metabolism and immune function pathways. We found a significant indirect effect of drought exposure on child body weight through cg03771070. Our results are the first to identify biological mediators linking severe drought to child growth in a low-income global hot spot for climate change. A better understanding of the mechanisms underlying the association between drought exposure and child growth is important to increasing climate change resilience by identifying targets for intervention.

Heavy metal blood concentrations in association with sociocultural characteristics, anthropometry and anemia among Kenyan adolescents

OBJECTIVES

To measure heavy metal concentrations among Kenyan youth and quantify associations with sociocultural, demographic, and health factors as well as anthropometry.

METHODS

Using data from a study of semi-nomadic pastoralists in Samburu County, Kenya, we measured blood concentrations of lead (Pb), mercury (Hg), and cadmium (Cd) in 161 adolescents. We identified sociocultural, demographic and health characteristics associated with each metal and quantified the association between metals and adolescent anthropometry.

RESULTS

Median blood concentrations of Pb, Cd, and Hg were 1.82 µg/dL, 0.24 µg/L and 0.16 µg/L, respectively. Place of residence (highlands vs lowlands) was a determinant of metal concentrations. Hg was inversely related to anemia, and metals were not associated with anthropometry.

CONCLUSIONS

In this population of Samburu adolescents, median Pb and Cd blood concentrations were higher than other North American or European biomonitoring studies. These findings motivate further investigation into the environmental sources of metals in this community.

Mineral Nutrition of Samburu Adolescents: A Comparative Study of Pastoralist Communities in Kenya

Objectives

This study aimed to characterize mineral nutrition (copper, magnesium, selenium, and zinc) in Samburu pastoralist youth, in the context of differential cultural transitions due to uneven changes in educational access, herding intensity, polygyny, and access to wild, domesticated, and market-sourced foods.

Materials and Methods

Whole dried blood spots were collected in a total of 161 youth (highlands, n = 97; lowlands, n = 64) to assess concentrations of: cadmium, copper, lead, magnesium, mercury, selenium, and zinc. Concentrations were determined through Inductively Coupled Mass Spectrometry. Dietary intakes were assessed by 24-hour recall method and calculation of probability of inadequate intakes. WHO protocols were applied to collect anthropometric measures in the youth.

Results

Nearly half of the adolescents (47.8%) fell below the reference range for zinc status, and 88.2% had low zinc-to-copper ratios. High probability of nutrient inadequacies were evident for protein, fat, vitamins A, B12, C, and E. In generalized linear modeling, lowland residence was negatively associated with zinc status and the zinc-to-copper ratio, and positively correlated with selenium and copper status. Other significant correlates were: dairy livestock ownership; wife number of the youth's mother; meat consumption; vegetable consumption; protein intake; infectious disease morbidities; BMI; and hemoglobin concentrations.

Discussion

In recent decades, Samburu pastoralists of northern Kenya have experienced marked dietary changes in the context of market integration, extreme drought, diminishing pasture availability, and violent civil conflict. Some children (particularly boys) successfully supplement their diets by foraging for wild foods, while others (particularly actively herding girls) may be more vulnerable.

Family socioeconomic status and child telomere length among the Samburu of Kenya

Previous research in high-income countries suggests that children from families with lower socioeconomic status (SES) tend to have shorter telomere length - a biomarker of stress and cell aging - than children from families with greater social and economic resources. However, little is known about predictors of child telomere length in low-income settings. Data for the current study are from a sample of 214 Samburu children aged 1-9 years. The Samburu are semi-nomadic pastoralists who live in the Rift Valley of north-central Kenya. Samburu livelihood is based primarily on livestock, and polygynous marriage is common. Drawing on prior ethnographic research, we measured 14 culturally relevant indicators of family SES, including mother's education, head of household's education, whether the child is currently attending school, household spending, mother's employment history, head of household's employment history, mother's perceived wealth, whether the child lives in a modern house, livestock holdings (total, cows, sheep/goats, and camels), mother's wife number, and whether the child lives in a polygynous household. Telomere length was measured in salivary DNA by the quantitative polymerase chain reaction (qPCR) method. Using latent class analysis, we identified four groups of children that are similar based on the 14 indicators of family SES: Lower SES; Middle SES, Traditional; Middle SES, Modern; and Higher SES. SES classes were not significantly associated with child telomere length. In models examining individual indicators of SES, we found that telomere length was 0.57 standard deviations greater for children who lived in families in the lowest quartile of total livestock holdings compared to those in the highest quartile (b = 0.57, p = 0.03). While additional research is needed to identify the mechanisms underlying this counterintuitive finding, the current study highlights the importance of cultural context in shaping the social gradient in health.