Sex disparities in COVID-19 outcomes in the United States: Quantifying and contextualizing variation.

This paper presents the first longitudinal study of sex disparities in COVID-19 cases and mortalities across U.S. states, derived from the unique 13-month dataset of the U.S. Gender/Sex COVID-19 Data Tracker. To analyze sex disparities, weekly case and mortality rates by sex and mortality rate ratios were computed for each U.S. state, and a multilevel crossed-effects conditional logistic binomial regression model was fitted to estimate the variation of the sex disparity in mortality over time and across states. Results demonstrate considerable variation in the sex disparity in COVID-19 cases and mortalities over time and between states. These data suggest that the sex disparity, when present, is modest, and likely varies in relation to context-sensitive variables, which may include health behaviors, preexisting health status, occupation, race/ethnicity, and other markers of social experience.

The future of sperm: a biovariability framework for understanding global sperm count trends.

The past 50 years have seen heated debate in the reproductive sciences about global trends in human sperm count. In 2017, Levine and colleagues published the largest and most methodologically rigorous meta-regression analysis to date and reported that average total sperm concentration among men from 'Western' countries has decreased by 59.3% since 1973, with no sign of halting. These results reverberated in the scientific community and in public discussions about men and masculinity in the modern world, in part because of scientists' public-facing claims about the societal implications of the decline of male fertility. We find that existing research follows a set of implicit and explicit assumptions about how to measure and interpret sperm counts, which collectively form what we term the Sperm Count Decline hypothesis (SCD). Using the study by Levine and colleagues, we identify weaknesses and inconsistencies in the SCD, and propose an alternative framework to guide research on sperm count trends: the Sperm Count Biovariability hypothesis (SCB). SCB asserts that sperm count varies within a wide range, much of which can be considered non-pathological and species-typical. Knowledge about the relationship between individual and population sperm count and life-historical and ecological factors is critical to interpreting trends in average sperm counts and their relationships to health and fertility.

A life history approach to prenatal supplementation: Building a bridge from biological anthropology to public health and nutrition.

While prenatal supplementation with protein, lipids, carbohydrates, and micronutrients has been used to improve infant outcomes in undernourished populations since the 1960s with inconsistent results, a flourishing body of literature within biological anthropology has used life history theory to explain why supplemental resources are often allocated to maternal survival and future reproduction and not to the current offspring. To date, however, public health and nutrition researchers have not adopted evolutionary perspectives in designing or analyzing prenatal supplementation studies. The result is a long series of supplementation trials with unpredictable and often disappointing outcomes for women and children, as well as serious lacunae in the understanding of long-term consequences of supplementation for women. The goal of this article is to open a tactical conversation about how to build a bridge between the evolutionary logic of biological anthropology and the evidentiary standards and methods of public health and nutrition with the aim of advancing knowledge about reproductive and metabolic physiology and improving women's health over the life course. The article reviews recent prenatal supplementation studies and proposes programmatic strategies by which biological anthropologists and public health and nutrition workers may collaborate to define different conditions of prenatal supplement resource allocation and to target more effective interventions.

Energetics and the immune system: Trade-offs associated with non-acute levels of CRP in adolescent Gambian girls.

BACKGROUND AND OBJECTIVES: The human immune system is an ever-changing composition of innumerable cells and proteins, continually ready to respond to pathogens or insults. The cost of maintaining this state of immunological readiness is rarely considered. In this paper we aim to discern a cost to non-acute immune function by investigating how low levels of C-reactive protein (CRP) relate to other energetic demands and resources in adolescent Gambian girls. METHODOLOGY: Data from a longitudinal study of 66 adolescent girls was used to test hypotheses around investment in immune function. Non-acute (under 2 mg/L) CRP was used as an index of immune function. Predictor variables include linear height velocity, adiposity, leptin, and measures of energy balance. RESULTS: Non-acute log CRP was positively associated with adiposity (ß = 0.16, p < 0.001, R2 = 0.17) and levels of the adipokine leptin (ß = 1.17, p = 0.006, R2 = 0.09). CRP was also negatively associated with increased investment in growth, as measured by height velocity (ß = -0.58, p < 0.001, R2 = 0.13) and lean mass deposition ß = -0.42, p = 0.005, R2 = 0.08). Relationships between adiposity and growth explained some, but not all, of this association. We do not find that CRP was related to energy balance. CONCLUSIONS AND IMPLICATIONS: These data support a hypothesis that investment in non-acute immune function is facultative, and sensitive to energetic resources and demands. We also find support for an adaptive association between the immune system and adipose tissue.

Endocrine responses, weight change, and energy sparing mechanisms during Ramadan among Gambian adolescent women.

OBJECTIVES: Ramadan fasting imposes a diurnal rather than a chronic energetic challenge. When Ramadan occurs during the agricultural season in subsistence populations, diurnal and chronic effects combine. The impact of layered energetic challenges on adolescent activity, metabolism, and body composition have not been quantified. This study compares the effects of a Ramadan (30 July-3 October 2009) and subsequent non-Ramadan (14 July-12 August 2010) agricultural season in 67 Gambian subsistence agriculturalist women between 14 and 20 years old. METHODS: Researchers collected body composition, anthropometric, metabolic, and activity data. Metabolic hormones were measured in weekly urine (C-peptide of insulin) and serum (leptin). Energy expenditure was estimated from heart rate calibrated for oxygen consumption. RESULTS: Participants lost more weight (Wald Chi-square 8.7, P < 0.01) and lean mass (Wald Chi-square 4.7, P < 0.05) in Ramadan than in the non-Ramadan agricultural season. Energy expenditure was lower (Wald Chi-square 11.2, P = 0.001) and there was a negative correlation between resting metabolic rate and energy expenditure in activity (R(2) = 0.097, F = 5.366, P = 0.025) during Ramadan. Leptin and C-peptide were higher during Ramadan (Wald Chi-square 53.7, P < 0.001 and Wald Chi-square 15.0, P < 0.001). CONCLUSIONS: Even using energy sparing behaviors, adolescent women enter negative energy balance when Ramadan and the agricultural season co-occur. Metabolic physiology shows a transient response to high glycemic index foods consumed at night. Older and larger individuals sustain greater losses during Ramadan.

The adolescent transition under energetic stress: Body composition tradeoffs among adolescent women in The Gambia.

BACKGROUND AND OBJECTIVES: Life history theory predicts a shift in energy allocation from growth to reproductive function as a consequence of puberty. During adolescence, linear growth tapers off and, in females, ovarian steroid production increases. In this model, acquisition of lean mass is associated with growth while investment in adiposity is associated with reproduction. This study examines the chronological and developmental predictors of energy allocation patterns among adolescent women under conditions of energy constraint. METHODOLOGY: Fifty post-menarcheal adolescent women between 14 and 20 years old were sampled for weight and body composition at the beginning and end of 1 month in an energy-adequate season and 1 month in the subsequent energy-constrained season in a rural province of The Gambia. RESULTS: Chronologically and developmentally younger adolescent girls gain weight in the form of lean mass in both energy-adequate and energy-constrained seasons, whereas older adolescents lose lean mass under conditions of energetic stress (generalized estimating equation (GEE) Wald chi-square comparing youngest tertile with older two tertiles 9.750, P = 0.002; GEE Wald chi-square comparing fast- with slow-growing individuals for growth rate 19.806, P < 0.001). When energy is limited, younger adolescents lose and older adolescents maintain fat (GEE Wald chi-square for interaction of age and season 6.568, P = 0.010; GEE Wald chi-square comparing fast- with slow-growing individuals for interaction of growth rate and season 7.807, P = 0.005). CONCLUSIONS AND IMPLICATIONS: When energy is constrained, the physiology of younger adolescents invests in growth while that of older adolescent females privileges reproductively valuable adipose tissue.

Puberty as a life history transition.

BACKGROUND: James Tanner's landmark publication, Growth at Adolescence, was not only the first and most comprehensive treatise on the subject of human pubertal development of its time, its core insights have held up remarkably well over time. REVIEW: This review connects Tanner's contributions to contemporary understanding of puberty as a process fundamentally driven by neuroendocrine maturation. It introduces the concepts of the 'hour-glass of puberty' and 'somatic strategy' as heuristic constructs. The 'hour-glass of puberty' describes the converging pathways of information flow influencing the timing of the neuroendocrine events of puberty and its ramifying consequences throughout the body. Somatic strategy refers to the pattern of sex-specific, adult body morphology that develops at puberty as the individual undergoes a life history transition from juvenile to adult.

Pooled energy budget and human life history.

Human life history contains a series of paradoxes not easily explained by classical life history theory. Although overall reproductive output is higher than in related primates, juvenile growth is slower and age-specific reproductive rates decline faster with age. A simple energetic model would predict that growth and reproductive rates should be positively correlated and that reproductive effort should not decelerate with age. The pattern of negative correlations in humans suggest the presence of trade-offs among peak reproductive rate, childhood growth, and reproductive rate at older ages. To address this puzzle, we propose a synthesis of reproductive ecology and behavioral ecology focused on intra- and inter-somatic energy transfers. This integration includes three concepts: the mother as final common pathway through which energy must pass to result in offspring; a distinction between direct and indirect reproductive effort, proposing the latter as a novel net energy allocation category relative to growth and direct reproductive effort; and a pooled energy budget representing the energetic contributions and withdrawals of all members of a breeding community. Individuals at all reproductive life stages are considered in light of their contributions to the pooled energy budget.

Active ghrelin levels across time and associations with leptin and anthropometrics in healthy ache Amerindian women of Paraguay.

Active (acylated) ghrelin is a peptide hormone secreted primarily by the stomach, positively associated with fasting, orexigenic, and promotes growth hormone secretion. It is therefore important to energy intake management. The objective of this pilot research was to (1) compare active ghrelin with previous measurements of leptin and anthropometrics; (2) assess the consistency of active ghrelin across time in this population; (3) extend our understanding of potential population variation in active ghrelin. Two serum samples separated by 10 days at the same time between meals were collected from healthy Ache women (n = 12, mean age 32.2 +/- 14.0 SD) to determine consistency over time, associations with leptin, and anthropmetric values. Mean active ghrelin was 72.9 +/- 23.0 pg/ml, highly correlated (r(2) = 0.95, P < 0.0001) between collections, and showed no paired mean differences (P < 0.18). There was no significant correlation with leptin, age, or anthropometric measures. Active ghrelin appears to be consistent over time in this population, perhaps reflecting regimented meal schedules and less interpopulation variation compared to leptin.

Links between physical fitness and cardiovascular reactivity and recovery to psychological stressors: A meta-analysis.

A meta-analysis of published studies with adult human participants was conducted to evaluate whether physical fitness attenuates cardiovascular reactivity and improves recovery from acute psychological stressors. Thirty-three studies met selection criteria; 18 were included in recovery analyses. Effect sizes and moderator influences were calculated by using meta-analysis software. A fixed effects model was fit initially; however, between-studies heterogeneity could not be explained even after inclusion of moderators. Therefore, to account for residual heterogeneity, a random effects model was estimated. Under this model, fit individuals showed significantly attenuated heart rate and systolic blood pressure reactivity and a trend toward attenuated diastolic blood pressure reactivity. Fit individuals also showed faster heart rate recovery, but there were no significant differences in systolic blood pressure or diastolic blood pressure recovery. No significant moderators emerged. Results have important implications for elucidating mechanisms underlying effects of fitness on cardiovascular disease and suggest that fitness may be an important confound in studies of stress reactivity.