C-reactive protein (CRP) in high altitude Bolivian peri-urban adolescents varies by adiposity, current illness, height, socioeconomic status, sex, and menarcheal status: The potential benefits and costs of adipose reserves in arduous environments.

OBJECTIVES: In non-industrialized and low-income populations, adipose stores can serve as a valuable buffer against harsh conditions such as seasonal food scarcity. However, these reserves may incur costs due to adipocytes' production of pro-inflammatory cytokines; inflammation is associated with increased risk for cardiometabolic diseases later in life. Life history theory posits that, especially in populations with high juvenile mortality, higher adiposity may nonetheless be advantageous if its benefits in early life outweigh its later costs. Relatively little is known about adolescents' C-reactive protein concentration (CRP; an inflammation biomarker) in such environments. We investigated CRP and its associations with several hypothesized predictors in adolescents in an economically diverse peri-urban Andean community. METHODS: We measured CRP in dried blood spots and collected data on anthropometrics, illnesses, socioeconomic status (SES), and menarcheal status in 59 female and 40 male adolescents ("Alteños", 11.0-14.9 years old) with normal vital signs in El Alto, Bolivia (~4150 m amsl). We used Cole's LMS method to standardize all anthropometrics for sex and age, and principal components analysis to construct a "fat-factor" variable loading on these standardized z-scores. We used multiple linear regression to assess the influence of fat-factor and other likely predictors on CRP rank. RESULTS: Compared to a national Bolivian growth reference, Alteños were, on average, shorter and leaner; only 6% were classified as overweight and none were obese. Pre-menarche females were on average leaner than post-menarche females. The best-fitting model explained 24% of the variance in CRP rank. Significant predictors were fat-factor, SES, current illness for males and pre-menarche females, and z-height for females. CONCLUSIONS: Our results are consistent with a tradeoff between investments in growth versus immune functioning, as might be expected in an environment with limited resources and high pathogen exposure (e.g., soil-transmitted helminths, poor sanitation). Thinner Alteños appear to maintain a minimum CRP concentration independent of fat-factor, while fatter (or less-thin) Alteños' CRP rises with fat-factor. Female Alteños appear to be trading off investment in immune response for investment in growth and maturation. Alteños' high rate of stunting and absence of obesity suggests chronic, presumably multifactorial, stress. Adipose stores likely buffer against some of these stressors and, in an environment such as this-in which many lack sufficient nutritious foods, potable water, adequate sewage, and health care-may confer a net lifetime benefit.

OBJETIVOS: En poblaciones no industrializadas y de bajos ingresos, las reservas adiposas pueden servir como un valioso amortiguador frente a condiciones duras como la escasez estacional de alimentos. Sin embargo, estas reservas pueden tener un coste debido a la producción de citoquinas proinflamatorias por parte de los adipocitos; la inflamación se asocia a un mayor riesgo de enfermedades cardiometabólicas en etapas posteriores de la vida. La teoría de la historia vital postula que, especialmente en poblaciones con una elevada mortalidad juvenil, una mayor adiposidad puede ser ventajosa si sus beneficios en los primeros años de vida compensan sus costes posteriores. Se sabe relativamente poco sobre la concentración de proteína C reactiva (PCR; un biomarcador de inflamación) de los adolescentes. Investigamos la PCR y sus asociaciones con varios predictores hipotéticos en adolescentes de una comunidad andina periurbana económicamente diversa. MÉTODOS: Se midió la PCR en muestras de sangre seca y se recogieron datos sobre antropometría, enfermedades, nivel socioeconómico (NSE) y menarquia en 59 mujeres y 40 varones adolescentes («alteños¼, 11,0­14,9 años de edad) con signos vitales normales en El Alto, Bolivia (~4150m amsl). Usamos el método LMS de Cole para estandarizar todos los parámetros antropométricos para sexo y edad, y análisis de componentes principales para construir una variable «factor de grasa¼ cargada en estos puntajes z­estandarizados. Se utilizó la regresión lineal múltiple para evaluar la influencia del factor grasa y otros posibles predictores en el rango de la PCR. RESULTADOS: En comparación con una referencia nacional boliviana de crecimiento, los alteños eran, en promedio, más bajos y más delgados; sólo el 6% estaban clasificados con sobrepeso y ninguno era obeso. Las chicas premenárquicos eran, en promedio, más delgados que las chicas postmenárquicos. El modelo de regresión que mejor se ajustaba explicaba el 24% de la varianza en el rango de PCR. Observamos una nueva asociación entre la adiposidad y la PCR. Cuando el factor adiposidad es >0, el rango de la PCR aumenta linealmente con el factor adiposidad. Cuando el factor adiposidad es <0, la PCR no varía con el factor adiposidad. Estos patrones sugieren que los Alteños más delgados mantienen una concentración mínima de PCR independiente del factor adiposidad, mientras que la PCR de los Alteños más gordos (menos delgados) aumenta con el factor adiposidad. Además, existe una mayor variación en el rango de la PCR en los adolescentes más delgados que en los más gordos. El autoinforme de una enfermedad actual en niños y niñas premenárquicas se asoció con una PCR significativamente más alta. La ausencia de una asociación significativa entre la enfermedad actual y la PCR en las chicas postmenárquicas puede reflejar confusión por cambios en la PCR durante el ciclo menstrual. Manteniendo constantes todos los demás factores predictivos, la PCR aumentó con el incremento del nivel socioeconómico. En las niñas, el aumento de la estatura se asoció a una disminución de la PCR, lo que sugiere que las niñas favorecen la inversión en crecimiento y maduración frente a la inversión en respuestas inmunitarias inflamatorias a corto plazo. En los chicos, no se observó una relación significativa entre la estatura y la PCR. La baja estatura y la delgadez de estos adolescentes sugieren que pueden estar invirtiendo en defensas humorales a más largo plazo (por ejemplo, anticuerpos contra helmintos), pero esta hipótesis requiere más estudios. CONCLUSIONES: La alta tasa de retraso en el crecimiento y la ausencia de obesidad de los alteños sugieren un estrés crónico, presumiblemente multifactorial. Muchas familias carecen de alimentos nutritivos suficientes, agua potable, alcantarillado adecuado y atención sanitaria. Es probable que las reservas adiposas amortigüen algunos de estos factores de estrés y confieran un beneficio neto a lo largo de la vida (la reducción de la mortalidad juvenil puede compensar cualquier aumento del riesgo de enfermedades cardiometabólicas en etapas posteriores de la vida). Sin embargo, estas compensaciones tienen un coste para los individuos y las sociedades. Reducir los riesgos de patógenos y mejorar la capacidad de los habitantes del altiplano para acceder sistemáticamente a agua limpia y a alimentos sanos suficientes y asequibles probablemente reportaría beneficios para la salud a lo largo de toda la vida.

Menstrual Cycle Characteristics of U. S. Adolescents According to Gynecologic Age and Age at Menarche.

STUDY OBJECTIVE: To characterize typical menstrual cycle characteristics in adolescents and determine how these differ with age at menarche or years since menarche (gynecologic age). METHODS: We surveyed 13 to 18-year-old U.S. users of the Clue app (N = 6,486) and linked their responses to app-recorded cycle data (N=38,916 cycles). We analyzed cycle characteristics including cycle length, cycle variability, period length, experience of heavy flow, and dysmenorrhea in relation to gynecologic age and menarcheal age using mixed effects models. RESULTS: With increasing gynecologic age, we observed dose-dependent associations of lower odds of cycle irregularity (defined as cycles that were highly variable, short, or long) and higher odds of reporting ≥1 day of heavy flow. Individuals <1 year post-menarche had lower odds of heavy flow (Odds Ratio (OR) = 0.3; 95% confidence interval (CI): 0.1, 0.6), and increased odds of having a highly variable cycle (OR = 2.6; 95% CI: 1.3, 5.2) or short cycles (OR = 5.0; 95% CI: 2.3, 11.0) compared to those who were 6+ years post-menarche. We also found associations with early and late age at menarche. Compared to menarcheal age of 14+ years, menarcheal age ≤10 years was associated with shorter cycle length (ß = -1.63 days; 95% CI: -2.51, -0.75), increased odds of dysmenorrhea (OR = 3.2; 95% CI: 2.3, 4.6), and decreased odds of high cycle variability (OR = 0.8; 95% CI: 0.6, 1.0). CONCLUSION: Cycle characteristics in adolescence are associated with menarcheal age and gynecologic age. Notably, highly variable cycles are common, especially among those with younger gynecologic age or older menarcheal age.

Well-being in healthy Icelandic women varies with extreme seasonality in ambient light.

Seasonal variation in photoperiod may affect psychosocial and physical well-being in healthy persons. We tested this hypothesis in healthy pre-menopausal women, without a history of mood disorders, living year-round in Reykjavik, Iceland (64.1°N). Participants reported daily self-assessments of well-being throughout a complete ovulatory menstrual cycle in summer and/or winter (70% participated in both seasons). Scores for mood, cognitive acuity, social support, physical health and a composite of these four indicators were each significantly higher in summer than in winter (linear mixed effects models: p < .001 for each model); tiredness did not differ by season. The effect of season was not significantly changed by inclusion of body mass index and/or age as covariates. Some prior studies have been hampered by sparse time sampling, inattention to covariates and/or relying on recalled data. This is to our knowledge the first investigation to test the study hypothesis with daily real-time data spanning complete ovulatory menstrual cycles in each of two seasons. This dense sampling has revealed modest seasonal variation in well-being in healthy women. Daylength (sunlight exposure) is likely a major, but not necessarily sole, factor in these seasonal differences in well-being; temperature is likely less important given Iceland's relatively moderate (for its high latitude) seasonal temperature swings.

Associations Among Menstrual Cycle Length, Coronavirus Disease 2019 (COVID-19), and Vaccination.

OBJECTIVE: To assess whether coronavirus disease 2019 (COVID-19) is associated with menstrual cycle length changes and, if so, how that compares with those undergoing vaccination or no event (control). METHODS: We conducted a retrospective cohort analysis in which we analyzed prospectively tracked cycle-length data from users of a period tracker application who also responded to a survey regarding COVID-19 symptoms and vaccination. We restricted our sample to users aged 16-45 years, with normal cycle lengths (24-38 days) and regular tracking behavior during the five cycles around COVID-19 symptoms or vaccination or a similar time period for those experiencing no event (control group). We calculated the within-user change in cycle length (days) from the three consecutive cycles preevent average (either vaccination, disease, or neither; cycles 1-3) to the event (cycle 4) and postevent (cycle 5) cycles. We used mixed-effects models to estimate the age- and country-adjusted difference in change in cycle length across the groups. RESULTS: We included 6,514 users from 110 countries representing 32,570 cycles (COVID-19 symptoms: 1,450; COVID-19 vaccination: 4,643; control: 421). The COVID-19 cohort experienced a 1.45-day adjusted increase in cycle length during cycle 4 (COVID-19) compared with their three preevent cycles (95% CI 0.86-2.04). The vaccinated group experienced a 1.14-day adjusted increase in cycle length during cycle 4 (COVID-19 vaccine) compared with their preevent average (95% CI 0.60-1.69). The control group (neither vaccine nor disease) experienced a 0.68-day decrease (95% CI -1.18 to -0.19) in a similar time period. Post hoc tests showed no significant differences in the magnitude of changes between the COVID-19 and vaccination cohorts. In both cohorts, cycle length changes disappeared in the postevent cycle. CONCLUSION: Experiencing COVID-19 is associated with a small change in cycle length similar to COVID-19 vaccination. These changes resolve quickly within the next cycle.

Assessment of App-Based Versus Conventional Survey Modalities for Reproductive Health Research in India, South Africa, and the United States: Comparative Cross-Sectional Study.

BACKGROUND: There is a widely acknowledged global need for more research on reproductive health (including contraception, menstrual health, sexuality, and maternal morbidities) and its impact on overall well-being. However, several factors-notably, high costs, considerable effort, and the sensitivity of these topics-impede the collection of the necessary data, especially in less accessible and lower-income populations. The burgeoning ownership of smartphones and growing use of menstrual tracking apps (MTAs) may present an opportunity to conduct reproductive health research with fewer impediments than those associated with conventional survey methods. OBJECTIVE: The main objective was to ascertain the feasibility, potential usefulness, and limitations of conducting reproductive health research using a mainstream MTA. METHODS: In each of the 3 countries, we evaluated questionnaire responses from (1) current users of an MTA (Clue) and (2) participants surveyed using conventional survey modalities (in-person interviews, SMS text messaging, and web-based questionnaires). We compared these responses with published data collected from large nationally representative benchmark samples (the United States Census and the Demographic and Health Surveys for South Africa and India). RESULTS: Given a sufficiently large user base, app-distributed surveys were able to quickly capture large samples on par with other methods and at low cost, with the additional advantage of being able to deploy remotely and simultaneously across countries. In each country, neither the app nor the conventional modality sample emerged as a consistently closer match to the distributions of the demographic attributes and the patterns of contraceptive use reported for the respective benchmark sample. Despite efforts to obtain representative samples, the conventional modality samples sometimes over- and other times underrepresented some subgroups (eg, underrepresentation of married persons in the United States and overrepresentation of rural residents in India). In all 3 countries, app users were younger, more educated, more likely to be urban residents, and more likely to use nonhormonal rather than hormonal contraceptive methods compared with the respective national benchmark. App users, compared with the conventional modality samples, consistently reported being more comfortable discussing their menstrual periods with other persons (eg, family, friends, and health care providers), suggesting that MTA users may be more likely to respond truthfully to questions on sensitive or taboo health topics. The app samples' consistency across countries regarding users' demographic profiles, contraceptive choices, and personal attitudes toward menstruation supports the validity of making cross-country comparisons of survey findings for a given app's users. CONCLUSIONS: MTAs such as Clue can provide a quick, scalable, and cost-effective method for collecting health data, including on sensitive topics, across a wide variety of settings and countries. With expanding global access to technology and the increasing use of these tools, consumer MTAs can be a viable survey modality to strengthen reproductive health research.

The Link Between Age and Partner Preferences in a Large, International Sample of Single Women.

Women's capacity to reproduce varies over the life span, and developmental goals such as family formation are age-graded and shaped by social norms about the appropriate age for completing specific developmental tasks. Thus, a woman's age may be linked to her ideas about what an ideal partner should be like. With the goals of replicating and extending prior research, in this study we examined the role of age in women's partner preferences across the globe. We investigated associations of age with ideal long-term partner preferences in a cross-cultural sample of 17,254 single (i.e., unpartnered) heterosexual women, ages 18 to 67, from 147 countries. Data were collected via an online questionnaire, the Ideal Partner Survey. Confirming our preregistered hypotheses, we found no or only negligible age effects on preferences for kindness-supportiveness, attractiveness, financial security-successfulness, or education-intelligence. Age was, however, positively associated with preferences for confidence-assertiveness. Consistent with family formation goals, age was associated with an ideal partner's parenting intentions (high until approximately age 30, then decreasing afterward). Age range deemed acceptable (and in particular, the discrepancy between one's own age and the minimum ideal age of a partner) increased with age. This latter pattern also replicated in exploratory analyses based on subsamples of lesbian and bisexual women. In summary, age has a limited impact on partner preferences. Of the attributes investigated, only preference for confidence-assertiveness was linked with age. However, age range deemed acceptable and an ideal partner's parenting intention, a dimension mostly neglected in earlier research, substantially vary with age.

More than blood: app-tracking reveals variability in heavy menstrual bleeding construct.

BACKGROUND: Heavy menstrual bleeding (HMB) is associated with impaired quality of life and may signal serious health problems. Unresolved challenges in measuring menstrual bleeding and identifying HMB have hampered research and clinical care. Self-reported bleeding histories are commonly used but these may be influenced by recall bias, personal beliefs regarding "normal" flow volume, and the experience of other physical symptoms or disruptions to daily life. The potential usefulness of menstrual-tracking mobile applications, which allow real-time user-entered data recording, for assessing HMB has not been studied. We evaluated recall bias in reported period duration, the relationship of tracked period duration and daily flow volume to subsequently reported period heaviness, variation in quality of life associated with increasing period heaviness, and the advantages and limitations of using app-tracked data for clinical and research purposes. METHODS: An online questionnaire was distributed to current users of Clue, a commercially available menstrual health tracking app, asking them to characterize their last period. We compared responses to the user's corresponding Clue app-tracked data. The study sample comprised 6546 U.S.-based users (aged 18-45 years). RESULTS: Increasing reported heaviness was associated with increasing app-tracked period length and days of heavy flow, impaired quality-of-life (especially body pain severity), and disrupted activities. Of those reporting having had a heavy/very heavy period, ~ 18% had not tracked any heavy flow, but their period length and quality-of-life indicators were similar to those who had tracked heavy flow. Sexual/romantic activities were the most affected across all flow volumes. Compared to app-tracked data, 44% recalled their exact period length; 83% recalled within ± 1 day. Overestimation was more common than underestimation. However, those with longer app-tracked periods were more likely to underestimate period length by ≥ 2 days, a pattern which could contribute to under-diagnosis of HMB. CONCLUSION: Period heaviness is a complex construct that encapsulates flow volume and, for many, several other bleeding-associated experiences (period length, bodily impairments, disruptions of daily activities). Even very precise flow volume assessments cannot capture the multi-faceted nature of HMB as experienced by the individual. Real-time app-tracking facilitates quick daily recording of several aspects of bleeding-associated experiences. This more reliable and detailed characterization of bleeding patterns and experiences can potentially increase understanding of menstrual bleeding variability and, if needed, help to guide treatment.

Socioeconomic impacts on Andean adolescents' growth: Variation between households, between communities and over time.

Background/Objectives: We evaluated potential socioeconomic contributors to variation in Andean adolescents' growth between households within a peri-urban community undergoing rapid demographic and economic change, between different community types (rural, peri-urban, urban) and over time. Because growth monitoring is widely used for assessing community needs and progress, we compared the prevalences of stunting, underweight, and overweight estimated by three different growth references. Methods: Anthropometrics of 101 El Alto, Bolivia, adolescents (Alteños), 11.0-14.9 years old in 2003, were compared between households (economic status assessed by parental occupations); to one urban and two rural samples collected in 1983/1998/1977, respectively; and to the WHO growth reference, a representative sample of Bolivian children (MESA), and a region-wide sample of high-altitude Peruvian children (Puno). Results: Female Alteños' growth was positively associated with household and maternal income indices. Alteños' height averaged ∼0.8SD/∼0.6SD/∼2SDs greater than adolescents' height in urban and rural communities measured in 1983/1998/1977, respectively. Overweight prevalence was comparable to the WHO, and lower than MESA and Puno, references. Stunting was 8.5/2.5/0.5 times WHO/MESA/Puno samples, respectively. Conclusions/Implications: Both peri-urban conditions and temporal trends contributed to gains in Alteños' growth. Rural out-migration can alleviate migrants' poverty, partly because of more diverse economic options in urbanized communities, especially for women. Nonetheless, Alteños averaged below WHO and MESA height and weight medians. Evolved biological adaptations to environmental challenges, and the consequent variability in growth trajectories, favor using multiple growth references. Growth monitoring should be informed by community- and household-level studies to detect and understand local factors causing or alleviating health disparities.

A predictive model for next cycle start date that accounts for adherence in menstrual self-tracking.

OBJECTIVE: The study sought to build predictive models of next menstrual cycle start date based on mobile health self-tracked cycle data. Because app users may skip tracking, disentangling physiological patterns of menstruation from tracking behaviors is necessary for the development of predictive models. MATERIALS AND METHODS: We use data from a popular menstrual tracker (186 000 menstruators with over 2 million tracked cycles) to learn a predictive model, which (1) accounts explicitly for self-tracking adherence; (2) updates predictions as a given cycle evolves, allowing for interpretable insight into how these predictions change over time; and (3) enables modeling of an individual's cycle length history while incorporating population-level information. RESULTS: Compared with 5 baselines (mean, median, convolutional neural network, recurrent neural network, and long short-term memory network), the model yields better predictions and consistently outperforms them as the cycle evolves. The model also provides predictions of skipped tracking probabilities. DISCUSSION: Mobile health apps such as menstrual trackers provide a rich source of self-tracked observations, but these data have questionable reliability, as they hinge on user adherence to the app. By taking a machine learning approach to modeling self-tracked cycle lengths, we can separate true cycle behavior from user adherence, allowing for more informed predictions and insights into the underlying observed data structure. CONCLUSIONS: Disentangling physiological patterns of menstruation from adherence allows for accurate and informative predictions of menstrual cycle start date and is necessary for mobile tracking apps. The proposed predictive model can support app users in being more aware of their self-tracking behavior and in better understanding their cycle dynamics.

Mind the gap: Contesting normal/abnormal constructs of human biology and behaviors.

Training in anthropology and evolutionary science ideally prepares scholars to recognize and challenge culturally grounded views of human variation. But upon inspection we find that idealized, and thus perhaps biased, conceptualizations of what is "normal" continue to permeate evaluations of human biology and behaviors. Each of the 13 contributions in this special issue on biological normalcy tackles these concerns as they pertain to some universal, but also variable, human biological or behavioral phenotype. These papers consider the ways in which the term "normal" is used in everyday life, in biomedicine, and in scientific studies to characterize some portion of the variability in a human phenotype. The contributors to this special issue, some of whom present original research findings, discuss the ongoing debates and challenges in the study of human biology and behavior, and critically examine how "normal" is used in their specific research area, thereby exposing and countering biases in the discourse on human phenotypic variation.

Recognizing normal reproductive biology: A comparative analysis of variability in menstrual cycle biomarkers in German and Bolivian women.

The idealized "normal" menstrual cycle typically comprises a coordinated ebb and flow of hormones over a 28-day span with ovulation invariably shown at the midpoint. It's a pretty picture-but rare. Systematic studies have debunked the myth that cycles occur regularly about every 28 days. However, assumptions persist regarding the extent and normalcy of variation in other cycle biomarkers. The processes of judging which phenotypic variants are "normal" is context dependent. In everyday life, normal is that which is most commonly seen. In biomedicine normal is often defined as an arbitrarily bounded portion of the phenotype's distribution about its statistical mean. Standards thus defined in one population are problematic when applied to other populations; population specific standards may also be suspect. Rather, recognizing normal female reproductive biology in diverse human populations requires specific knowledge of proximate mechanisms and functional context. Such efforts should be grounded in an empirical assessment of phenotypic variability. We tested hypotheses regarding cycle biomarker variability in women from a wealthy industrialized population (Germany) and a resource-limited rural agropastoral population (Bolivia). Ovulatory cycles in both samples displayed marked but nonetheless comparable variability in all cycle biomarkers and similar means/medians for cycle and phase lengths. Notably, cycle and phase lengths are poor predictors of mid-luteal progesterone concentrations. These patterns suggest that global and local statistical criteria for "normal" cycles would be difficult to define. A more productive approach involves elucidating the causes of natural variation in ovarian cycling and its consequences for reproductive success and women's health.

A Generative Modeling Approach to Calibrated Predictions: A Use Case on Menstrual Cycle Length Prediction.

We explore how to quantify uncertainty when designing predictive models for healthcare to provide well-calibrated results. Uncertainty quantification and calibration are critical in medicine, as one must not only accommodate the variability of the underlying physiology, but adjust to the uncertain data collection and reporting process. This occurs not only on the context of electronic health records (i.e., the clinical documentation process), but on mobile health as well (i.e., user specific self-tracking patterns must be accounted for). In this work, we show that accurate uncertainty estimation is directly relevant to an important health application: the prediction of menstrual cycle length, based on self-tracked information. We take advantage of a flexible generative model that accommodates under-dispersed distributions via two degrees of freedom to fit the mean and variance of the observed cycle lengths. From a machine learning perspective, our work showcases how flexible generative models can not only provide state-of-the art predictive accuracy, but enable well-calibrated predictions. From a healthcare perspective, we demonstrate that with flexible generative models, not only can we accommodate the idiosyncrasies of mobile health data, but we can also adjust the predictive uncertainty to per-user cycle length patterns. We evaluate the proposed model in real-world cycle length data collected by one of the most popular menstrual trackers worldwide, and demonstrate how the proposed generative model provides accurate and well-calibrated cycle length predictions. Providing meaningful, less uncertain cycle length predictions is beneficial for menstrual health researchers, mobile health users and developers, as it may help design more usable mobile health solutions.

Field methods and strategies for assessing female reproductive functioning.

A detailed understanding of female reproductive functioning is important to many disciplines including anthropology, evolutionary theory, demography, psychology, and biomedicine. In this article, I describe strategies and methods that have been used successfully in community-based studies of human reproduction, many in remote locales, to produce high quality biomarker data. These techniques are applicable to a wide range of research questions and populations, and to persons from adolescence through senescence. I give particular attention to the inherent challenges imposed by the cyclical and somewhat unpredictable nature of the hypothalamic-pituitary-ovarian axis including the necessity and difficulty of ascertaining the timing and occurrence of ovulation, the limits of different sampling regimes for capturing fluctuations in reproductive hormones, and the critical importance of recognizing and, when possible, reducing selection bias. I discuss the relative advantages and disadvantages of collecting saliva, urine, and dried blood spots, and describe some of the subtleties involved in collecting contamination-free samples. Once samples are collected, they must be stored in a manner that minimizes degradation; I describe techniques to keep samples cold even without access to electricity or dry ice. I also discuss various issues that should be considered during initial discussions with a laboratory and when samples are assayed by the laboratory. I include examples of techniques that have worked well in actual field studies, and examples of flawed analytical approaches that should be avoided. With these and other tools, even under technology-sparse conditions, researchers can investigate variability in human physiology across the breadth of human habitats.

Mobile sex-tech apps: How use differs across global areas of high and low gender equality.

Digital technologies are increasingly intertwined into people's sexual lives, with growing scholarly interest in the intersection of sex and technology (sex-tech). However, much of the literature is limited by its over emphasis on negative outcomes and the predominance of work by and about North Americans, creating the impression that sex-tech is largely a Western phenomenon. Based on responses from 130,885 women in 191 countries, we assessed how women around the world interact with mobile technology for sex-related purposes, and whether in areas of greater gender inequality, technological accessibility may be empowering women with knowledge about sexuality. We investigated women's use of technology to find sexual partners, learn about sex and improve their sexual relationships, and track their own sexual health. About one-fifth reported using mobile apps to find sexual partners. This use varied by region: about one-third in Oceania, one-fourth in Europe and the Americas, and one-fifth in Asia and Africa. Staying connected when apart was the most commonly selected reason for app use with a sexual partner. About one-third had used an app to track their own sexual activity. Very few reported that the app they used to improve their sexual relationships was detrimental (0.2%) or not useful (0.6%). Women in countries with greater gender inequality were less likely to have used mobile apps to find a sexual partner, but nearly four times more likely to have engaged in sending and receiving sexts. To our knowledge, this study provides the most comprehensive global data on sex-tech use thus far, demonstrates significant regional variations in sex-tech use, and is the first to examine women's engagement in sex-related mobile technology in locations with greater gender disparities. These findings may inform large-scale targeted studies, interventions, and sex education to improve the lives of women around the world.

Characterizing physiological and symptomatic variation in menstrual cycles using self-tracked mobile-health data.

The menstrual cycle is a key indicator of overall health for women of reproductive age. Previously, menstruation was primarily studied through survey results; however, as menstrual tracking mobile apps become more widely adopted, they provide an increasingly large, content-rich source of menstrual health experiences and behaviors over time. By exploring a database of user-tracked observations from the Clue app by BioWink GmbH of over 378,000 users and 4.9 million natural cycles, we show that self-reported menstrual tracker data can reveal statistically significant relationships between per-person cycle length variability and self-reported qualitative symptoms. A concern for self-tracked data is that they reflect not only physiological behaviors, but also the engagement dynamics of app users. To mitigate such potential artifacts, we develop a procedure to exclude cycles lacking user engagement, thereby allowing us to better distinguish true menstrual patterns from tracking anomalies. We uncover that women located at different ends of the menstrual variability spectrum, based on the consistency of their cycle length statistics, exhibit statistically significant differences in their cycle characteristics and symptom tracking patterns. We also find that cycle and period length statistics are stationary over the app usage timeline across the variability spectrum. The symptoms that we identify as showing statistically significant association with timing data can be useful to clinicians and users for predicting cycle variability from symptoms, or as potential health indicators for conditions like endometriosis. Our findings showcase the potential of longitudinal, high-resolution self-tracked data to improve understanding of menstruation and women's health as a whole.

Community, household, and individual correlates of sleep behaviors in Guyanese female youth.

OBJECTIVES: Chronic sleep loss among youth is a worldwide health problem. Since research on its predictors is often limited to high-income countries, it is unclear if these findings are generalizable to all populations. To address this gap from an ecological perspective, we evaluated the associations between adolescents' sleep behaviors and several factors at the community, household, and individual levels in a middle-income country. METHODS: This was a cross-sectional study of 73 girls (mean age = 14.5 y; range = 11-18 y) in rural and urban communities in Guyana. Sleep behaviors (nap-duration, bedtime, rise-time, night-bed-duration, and sleep-duration) were assessed with interviews and monitored up to 7 consecutive days using waist-worn accelerometers. RESULTS: Similar to other settings, Guyanese urban youth reported significantly later bedtimes than rural youth, and increasing age was associated with later bedtime and shorter night-bed-duration. In contrast to the association observed in high-income countries, increasing household poverty scores in Guyana were associated with longer night-bed-duration. CONCLUSIONS: Although the relationships between locale, age, and sleep in Guyana paralleled patterns seen in high-income countries, the positive relationship between poverty and sleep diverges from previous reports. These findings suggest that predictors of chronic sleep loss seen in high-income countries are likely to differ from those in middle- and low-income countries. More sleep studies in underrepresented populations are needed to gain a comprehensive understanding of adolescent sleep behavior and its correlates.

Corrigendum to: Decision making over condom use during menses to avert sexually transmissible infections.

Background:The aim of this study was to test the hypothesis that receptive partners in penile-vaginal intercourse (PVI) who exercise independent decision making over condom use during menses do so to avert sexually transmissible infection (STI) transmission or acquisition. Methods: Data were collected through a partnership with Clue, the industry-leading female health app. A brief web-based questionnaire was developed, translated into 10 languages, and made accessible via a URL link sent to Clue users and posted on social media. Inclusion criteria were: age ≥14 years, not being currently pregnant and engaging in PVI and condom use during menses in the past 3 months. The analytical subsample comprised 12889 respondents residing in 146 countries. Results: Twenty per cent indicated independent decision making about condom use during menses. Independent decision making was associated with lower odds of reporting that condoms were used for contraception (adjusted odds ratio (aOR) 0.65; 99% confidence interval (CI) 0.57-0.73) and higher odds that they were used for the prevention of STIs (aOR 1.44; 99% CI 1.28-1.61). A third significant finding pertained to always using condoms during menses; this was less likely among those indicating independent (female only) decision making (aOR 0.69; 99% CI 0.62-0.78). Non-significant associations with another two outcomes were found: protecting the partner against menstrual blood and protecting themselves against semen. Conclusions: Findings from people in 146 countries strongly support the hypothesis that those exercising independent decision making over condom use during menses do so to avert STI transmission or acquisition. That only one-fifth of this global sample reported this type of independent decision making suggests that empowerment-oriented (structural-level) interventions may be advantageous for individuals who are the receptive partner in PVI that occurs during menses.

Vaginal Glycogen, Not Estradiol, Is Associated With Vaginal Bacterial Community Composition in Black Adolescent Women.

PURPOSE: The purpose of this study was to characterize the composition of vaginal bacterial communities in a cohort of black adolescent women and to determine how the species composition of these communities correlates with levels of estradiol, glycogen, and stress. METHODS: Twenty-one black adolescent women were sampled longitudinally. The composition of their vaginal communities was determined by analyzing the sequences of the V1-V3 regions of 16S rRNA genes, and they were grouped based on patterns in species abundances. The relationships between estradiol, glycogen, psychosocial stress, and the composition of these communities were assessed. RESULTS: Vaginal communities could be distinguished and classified into three groups that differed in the abundances of Lactobacillus. Eighty-one percent of study participants had communities dominated by species of Lactobacillus. Glycogen levels were higher in communities dominated by one or multiple species of Lactobacillus compared with those having low proportions of Lactobacillus. Estradiol and psychosocial stress measurements did not differ among the three groups, whereas estradiol and glycogen exhibited a weak positive relationship that was not statistically significant. CONCLUSIONS: The findings of this pilot study suggest that glycogen levels are associated with vaginal community composition in young black women; however, estradiol and psychosocial stress are not. In addition, the results suggest there is no simple relationship between levels of estradiol and the production of vaginal glycogen.