ABSTRACTObjectiveThis study aims to investigate whether urinary cortisol can be reliably measured after long‐term storage at −20°C, using urine samples collected in 1993 from rural Bangladeshi women, and assayed after 16 and 30 years (2009 and 2023).MethodsSpecimens were collected by participants, placed in coolers with ice packs, transported to a field lab, and then refrigerated for up to 1 week before processing. Specific gravity was measured, and a 6.5 mL sample was archived at −20°C. Urinary cortisol was assayed in 2009 as part of a prior study using enzyme‐linked immunosorbent assay (ELISA). In 2023, cortisol was measured in a subsample of 200 specimens using the same assay.ResultsOf the 200 specimens, 7 (3.5%) were measured with low precision. Cortisol could not be detected in nine specimens (4.5%). In the remaining 184 specimens, urinary log cortisol levels measured in 2009 and 2023 were positively correlated (r = 0.973, 95% CI: 0.964–0.980; p < 0.0001 and nonparametric rs = 0.795; p < 0.0001). A paired t‐test revealed a bias toward slightly greater values in the 2023 measurements (p < 0.0001).ConclusionThese results suggest that urinary cortisol remains largely intact and measurable in specimens stored at −20°C for three decades, and there is a strong correlation between cortisol measured after 16 and 30 years in storage.

ABSTRACTThe menstrual cycle is increasingly described as a “vital sign of the female body,” with the literature suggesting cycle‐related brain and behavioral changes. With growing interest in the effects that the menstrual cycle has on the brain, body and mind, characterizing what constitutes healthy cycle‐related change has become a central goal of behavioral neuroendocrinology. Considering the epistemological importance of research in behavioral neuroendocrinology for shaping our understanding of cycle‐related effects in menstruating people, a critical examination of how the menstrual cycle is operationalized and studied in this field is warranted. In this narrative review, we first describe some methodological gold standards for investigating the menstrual cycle as an acontextual sex‐related neurohormonal phenomenon, while highlighting ongoing limitations. We then introduce alternative conceptualizations that operationalize the menstrual cycle as context‐contingent and demonstrate the importance of environmental experiences, particularly stress, in influencing cycle‐related brain and behavioral changes. Grounded in a feminist/queer approach to sex/gender difference, we propose a conceptualization of the menstrual cycle that integrates gendered sources of stress and discuss the potential of this approach to enable a more representative operationalization that better accounts for its inherent variability.

ABSTRACTHemoglobin concentration is often interpreted as a marker for total hemoglobin mass in studies investigating high‐altitude adaptation. However, hemoglobin concentration is determined by both plasma volume and total hemoglobin mass. Therefore, using hemoglobin concentration as a marker for hemoglobin mass can obscure variation in total hemoglobin mass and/or plasma volume and lead to flawed conclusions about adaptation. In this short commentary, we highlight examples from athletic, clinical and high‐altitude populations and responses to environmental stressors illustrating the dissociations between intravascular volumes and hemoglobin concentration. The reliance on hemoglobin concentration has reinforced the prevailing, but potentially incorrect, interpretation of blunted hypoxia‐induced erythropoiesis in Tibetan and Ethiopian highlanders. We argue that measures of plasma volume and total hemoglobin mass, which can easily be obtained using the carbon monoxide rebreathing technique, provide more physiologically relevant phenotypes. We propose that future genetic and evolutionary studies of high‐altitude adaptation should move beyond hemoglobin concentration and focus on measurements of total hemoglobin mass and intravascular volumes.

ABSTRACTObjectivesThis study aims to investigate the dynamic changes in the nutritional status of school‐age children in five cohorts with a two‐year follow‐up, encompassing a span of 7 years.MethodsUtilizing a mixed longitudinal design, we implemented five cohorts with a two‐year follow‐up, encompassing a span of 7 years. The study's total sample comprised 101 school‐age children (51 females and 50 males), aged between 6 and 11 years at the commencement of the follow‐up. Anthropometric variables were obtained following standardized procedures. Subsequently, the Body Mass Index (BMI) was derived using the formula BMI = body mass (kg)/(height)2. Nutritional status was classified according to established cutoff points for age and sex.ResultsThe prevalence rates for overweight, obesity, and underweight were found to be 22%, 10%, and 5%, respectively. Notably, the presence of overweight at the initiation of the follow‐up exhibited a significant association with the development of obesity after a two‐year period (χ2 = 5.325, p = 0.021). Furthermore, logistic regression analysis indicated that participants classified as “overweight” at the outset of the study were 4.7 times more likely (95% CI = 1.156–19.754) to develop obesity compared to their eutrophic counterparts.ConclusionThe study establishes a clear link between overweight status and the medium‐term development of obesity in school‐age children, aged between 6 and 11 years. These findings underscore the need for early intervention strategies and targeted preventive measures to address this concerning health issue.

ABSTRACTIn the aftermath of the 2009 H1N1 influenza A pandemic, research revealed the relationship between body size and the severity of influenza outcomes. However, there is little data available on body size in historical populations; therefore, the relationship between body size and 1918 influenza pandemic outcomes is virtually unknown. Alaskan death records from the Alaska Bureau of Vital Statistics with recorded height and mass at death (n = 2724) were analyzed to illuminate this relationship during both the pandemic (1918–20) and a non‐pandemic period (1917, 1921–25). Binomial logistic regression models were fit to predict the likelihood of a P&I death against four other major causes of death, first using only BMI as a predictor, then controlling for demographic variables. BMI alone can predict the probability of P&I death, but only during the pandemic period (p < 0.001). BMI (ORs = 0.90–1.51), all regions (ORs = 2.08–9.17), age (OR = 0.98), sex (male: OR = 0.66–0.75), and ethnicity group (non‐Alaska Native: OR = 0.36–0.37) significantly predicted the likelihood of a P&I death during the pandemic. The results suggest that as BMI increases, the risk of P&I death also increases with additional predictors, but only during the 1918 influenza pandemic period. There is no significant relationship between BMI and P&I death outside of pandemic years. This result may contribute an additional unique feature to our understanding of the 1918 influenza pandemic and its epidemiological novelty. This research further contributes new data on historical population biology and contextualizes results within the framework of developmental origins of health and disease for ultimate explanations of differential risks between Alaska Native and settler populations.

ABSTRACTObjectivesThe aim of this cross‐sectional study is to investigate the association between long‐term air pollution (AP) exposure and adiposity, primarily visceral fat and secondary body fat in runners and inactive participants.MethodsThis study included 945 individuals (male n = 505 and female n = 440). These included both active (runners: run ≥ 10 km/week) and inactive (did not follow the WHO 2020 PA recommendations) individuals. Dependent variables were body composition parameters fat mass index (FMI) and visceral fat (VFA), measured using dual‐emission X‐ray absorptiometry (DXA). A Hologic QDR (Horizon) bone densitometer was used for the measurement. Independent variables were AP values (PM10, PM2.5, NO2, BaP), for which lifetime exposure (LCxp) was calculated. Volume physical activity (PA), eating habits, and cardiorespiratory fitness (V̇O2peak) were analyzed as covariates.ResultsThe results showed that long‐term exposure to AP was not associated with increased adiposity (p > 0.05). However, age (p = 0.000), sex (p = 0.000), and V̇O2peak (p = 0.000) were associated with VFA. Values for VFA increased with age, males had higher VFA than females, and VFA values decreased with increasing V̇O2peak (p < 0.05) values. Furthermore, higher V̇O2peak values were strongly associated with lower FMI (p = 0.000).ConclusionsAdiposity was not associated with AP in the studied population. Adiposity was affected mainly by lifestyle and associated cardiorespiratory fitness presented by V̇O2peak values.

ABSTRACTBackgroundThyroid hormones (TH) regulate metabolism and are shaped by environmental factors—ambient temperature in particular. Previous work among indigenous and non‐indigenous populations in Russia revealed that there are seasonal shifts in TH dynamics such that total and free triiodothyronine (fT3) and free thyroxine (fT4) increase during winter. Elevated TH levels in these populations were positively correlated with the elevated resting metabolic rate (RMR) commonly seen among indigenous cold climate populations.MethodsHere we examined the relationship between TH levels (fT3, fT4, and thyroid stimulating hormone) and resting metabolism among reindeer herders (N = 35) and office workers (N = 16) from northern Finland in January 2019 and February of 2023. RMR was measured using indirect calorimetry at both time points and a TH analysis was conducted from venous blood samples collected before RMR measurements in 2023 only.ResultsControlling for fat free mass, female reindeer herders had significantly higher RMRs than male reindeer herders and significantly higher RMRs than predictive equation estimates. Female herders also had significantly higher fT3 and TSH than male herders and female officer workers. Female herders exhibited a significant positive correlation between fT4 and RMR; significant correlations were not found among male herders or female office workers.ConclusionThis preliminary study demonstrates variation in the relationship between TH levels and resting metabolism among reindeer herders and office workers in Northern Finland. These results highlight potential sex‐based differences in TH and metabolism dynamics, particularly among female reindeer herders, that require further research.