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(https://www.psypost.org/estradiol-levels-may-influence-the-success-of-exposure-therapy-in-women-study-finds/) Estradiol levels may influence the success of exposure therapy in women, study finds
Dec 29th 2024, 08:00

A recent study demonstrated that the ingestion of 2 mg of estradiol facilitates the extinction of a fear response but also contributes to its stronger return later. In contrast, the administration of progesterone did not show any effect on fear responses. The research was published in (https://doi.org/10.1038/s41398-024-03079-4) Translational Psychiatry.
Fear conditioning experiments in humans investigate how individuals learn to associate a neutral stimulus (e.g., a tone or light) with an aversive stimulus (e.g., a mild electric shock), leading to the development of a fear response. These experiments typically measure physiological responses, such as heart rate, skin conductance, or brain activity, to evaluate the conditioned fear response. Researchers believe that fear conditioning can help understand mechanisms underlying anxiety disorders, PTSD, and the processes of fear extinction, as these conditioned responses mimic how individuals with these disorders react to situations that trigger fear and anxiety.
In general, females are at a higher risk of developing anxiety and related disorders. Multiple studies suggest that the female sex hormones estradiol and progesterone may influence the development of fear and anxiety responses. These two hormones play key roles in regulating the female reproductive system and are primarily produced in the ovaries.
Estradiol is crucial for developing and maintaining secondary sexual characteristics, regulating the menstrual cycle, and preparing the uterine lining for pregnancy. Progesterone is essential for maintaining pregnancy by stabilizing the uterine lining and preventing contractions that could lead to miscarriage. During the menstrual cycle, estradiol levels peak before ovulation, stimulating the release of an egg, while progesterone rises in the second half of the cycle to support potential implantation.
Study author Michael Kaczmarczyk and his colleagues aimed to examine the effects of administering estradiol and progesterone on the development and extinction of fear responses in healthy women. They hypothesized that administering estradiol before extinction training (a process in which a participant learns to no longer react with fear to a previously fear-provoking stimulus) would enhance extinction learning and reduce the fear response in a later test designed to measure its return.
The study included 116 healthy premenopausal women with no psychiatric, gynecological, or endocrinological conditions. Their average age was 26 years. All participants were tested in the follicular phase of their menstrual cycle, and each received €120 for participation.
In the experiment, participants were seated in front of a monitor while two electrodes were attached to the back of their right hand. These electrodes delivered mild electric shocks, serving as an unconditioned stimulus (a stimulus that elicits a fear response) in the fear conditioning trials. Two additional electrodes were placed on the palm of the left hand to record skin conductance responses (changes in skin conductivity caused by sweating due to fear reactions). Researchers displayed photographs on the monitor showing a lamp that initially remained off. After a brief interval, the lamp would glow yellow, blue, or red for six seconds, followed by a black screen for 15 seconds.
During fear acquisition training on Day 1, participants received electric shocks after the lamp displayed two of the three colors. Through this process, they learned to associate these specific colors with the electric shock that followed, resulting in measurable fear responses, as detected by changes in skin conductance.
On the second day, participants were given three pills to take. There were four possible combinations of pills: placebo only, placebo + estradiol, placebo + progesterone, or estradiol + progesterone. All pills looked identical to ensure participants would not know which combination they received. Participants were randomly assigned to one of these combinations. The estradiol pill contained 2 mg of estradiolvalerat (Gynokadin®), while the progesterone dose was 400 mg, delivered in two pills (Utrogest®; 200 mg each). Two hours after taking the pills, participants underwent fear extinction training, during which lights previously associated with electric shocks were presented but no shocks were delivered.
On the final day, which focused on testing the return of fear, each of the lights was shown five times. This was followed by four electric shocks administered while participants sat in front of a gray monitor screen. Afterward, all three lights were presented again without shocks to assess whether fear reactions had returned. Before and after each training session, participants provided saliva samples, allowing researchers to measure estradiol and progesterone concentrations.
The results showed that participants successfully learned to associate certain lights with electric shocks, as indicated by increased skin conductance responses when presented with the conditioned lights. Estradiol administration on the day of fear extinction training accelerated the extinction process. In participants who received estradiol, the difference in skin conductance responses between lights associated with electric shocks and those not associated was reduced.
However, during the return of fear test on Day 3, participants who had received estradiol showed heightened skin conductance responses to the extinguished stimulus (lights) compared to the previous day. This indicated a stronger return of fear in the groups that received estradiol than in the other groups.
Progesterone administration had no significant effects on fear reactions.
“In our interpretation, exogenous estradiol administration affected the extinction of the conditioned fear response which led subsequently to a stronger return of fear. From a clinical perspective our findings suggest that estradiol levels may have an influence on the success of exposure therapy and could be taken into consideration when planning exposure sessions,” the study authors concluded.
The study sheds light on the effects of estradiol on fear responses. However, the participants were all young women and the study only included reactions to mild electric shock. Results on other demographic groups and looking at stronger fear reactions might differ.
The paper, “(https://doi.org/10.1038/s41398-024-03079-4) Effects of separate and combined estradiol and progesterone administration on fear extinction in healthy premenopausal women,” was authored by Michael Kaczmarczyk, Christian Eric Deuter, Hanna Deus, Anna Kallidou, Christian J. Merz, Julian Hellmann-Regen, Christian Otte, and Katja Wingenfeld.

(https://www.psypost.org/lonely-individuals-show-reduced-cardiovascular-adaptability-under-social-stress/) Lonely individuals show reduced cardiovascular adaptability under social stress
Dec 29th 2024, 06:00

A recent study published in (https://www.sciencedirect.com/science/article/abs/pii/S0301051124002230) Biological Psychology provides new insights into the link between loneliness and cardiovascular health. The research found that loneliness is associated with reduced heart rate variability during acute social stress, which suggests a decreased ability of the autonomic nervous system to regulate cardiovascular function. This effect was more pronounced in women than in men.
Loneliness is a deeply personal experience defined by a gap between the social connections an individual desires and what they actually have. It is not simply about being alone; rather, it reflects the subjective distress of feeling disconnected or unsupported by meaningful relationships. This sense of isolation, whether physical or emotional, has significant implications for mental and physical health.
Beyond feelings of unhappiness, loneliness is linked to a higher risk of chronic illnesses, particularly cardiovascular diseases such as heart attacks and strokes. Despite its importance, the physiological mechanisms that connect loneliness to such outcomes remain unclear, prompting researchers to explore the deeper biological underpinnings of this link.
“I have been focusing on the health impacts of loneliness for more than a decade. Over the years, our research team has conducted a series of population studies demonstrating that loneliness is a significant risk factor for various adverse health outcomes. Among these, cardiovascular health has consistently shown the strongest and most robust associations,” said
study author (http://faculty.tju.edu.cn/216183/en/index/37792/list/index.htm#hdjl) Bin Yu, an associate professor of health psychology at Tianjin University.
“Building on these findings, we turned our attention to the physiological mechanisms underlying the link between loneliness and cardiovascular health. Atypical cardiovascular reactivity to acute stress has been identified as a potential pathway contributing to negative cardiovascular outcomes. Previous studies have explored cardiac measures such as heart rate, blood pressure, and cardiac impedance in response to stress, but heart rate variability has been largely overlooked.”
Heart rate variability—a measure of the time differences between heartbeats—is an important indicator of autonomic function. High variability suggests a healthy, adaptable system, while reduced variability is linked to poor cardiovascular outcomes.
“Heart rate variability reflects autonomic nervous system functioning and its reactivity to stress is believed to play a critical role in cardiovascular health,” Yu explained. “This gap motivated us to conduct this study, focusing on cardiovascular reactivity to acute social stress among younger adults.”
The researchers recruited 97 college students aged 17 to 29, ensuring all participants were in good physical health and free from significant recent life events. Before the experiment, participants adhered to guidelines to avoid smoking, alcohol, and caffeine for 24 hours and abstained from eating for one hour. Of these, 92 participants (52 women) provided usable data after exclusions for poor-quality measurements.
To measure loneliness, the team used the revised UCLA Loneliness Scale, which assesses how often individuals feel disconnected from others. Participants also completed assessments of neuroticism, social network size, and mood to control for potential confounding factors.
The researchers induced acute social stress using the Trier Social Stress Test, a well-established protocol. This test involved a five-minute public speaking task followed by a mental arithmetic challenge, performed in front of evaluators who maintained a cold and evaluative demeanor. Heart rate variability and heart rate were monitored throughout the experiment using electrocardiogram equipment. The data were analyzed to compare participants’ physiological responses during baseline, stress, and recovery periods.
The researchers found that loneliness was associated with diminished heart rate variability reactivity during social stress, even after accounting for factors such as age, sex, and neuroticism. This reduced variability indicates that the autonomic nervous system of lonely individuals may be less effective at regulating cardiovascular responses under stress. In simpler terms, their bodies showed less flexibility in adapting to the demands of a stressful situation.
“During stress, cardiac measures such as heart rate and blood pressure typically increase, and earlier research has shown that lonely individuals may exhibit exaggerated or blunted reactivity to social stress,” Yu told PsyPost. “However, the implications of exaggerated or blunted reactivity for cardiovascular health remain debated.”
“In contrast, heart rate variability generally decreases under stress, and blunted cardiovascular reactivity is widely recognized as detrimental to cardiovascular health. Our study is the first to demonstrate that lonely individuals are more likely to exhibit blunted cardiovascular reactivity to acute social stress. These findings provide a potential physiological explanation for the link between loneliness and poorer cardiovascular health outcomes.”
Interestingly, the researchers observed notable differences between men and women. Women who reported higher levels of loneliness exhibited more significant reductions in heart rate variability reactivity, while no such association was found in men. This sex-specific pattern aligns with previous findings suggesting that women may rely more on social connections for stress regulation, making them more vulnerable to the physiological effects of loneliness.
“Overall, the findings were in line with our expectations,” Yu said. “However, we were slightly surprised to observe sex differences in the results. Specifically, the association between loneliness and cardiovascular reactivity was more pronounced among women. This opens a new avenue for understanding how gender might moderate the health effects of loneliness.”
Additionally, the study found that loneliness was linked to reduced heart rate reactivity during stress, further supporting the idea that loneliness affects the autonomic nervous system’s stress response. Importantly, the findings emphasize loneliness as a subjective experience, distinct from objective measures of social isolation such as the size of one’s social network.
As with all research, the study has limitations. Its cross-sectional design means the researchers could not establish a causal relationship between loneliness and reduced cardiovascular reactivity. Longitudinal studies would be needed to determine whether loneliness directly leads to these physiological changes or whether other factors are involved. The relatively small sample size, though adequate for this type of research, limits the generalizability of the results to broader populations.
“Most evidence linking loneliness to cardiovascular health comes from studies on older populations,” Yu noted. “While our findings suggest that the detrimental effects of loneliness may manifest earlier in life than previously thought, it is important to note that our sample consisted of young adults. As such, these results may not generalize to other age groups, particularly older adults. Future research should explore these associations across the lifespan to provide a more comprehensive understanding.”
Additionally, the study’s reliance on a laboratory setting may not fully capture how loneliness affects cardiovascular responses in real-world scenarios. To address this, Yu and his colleagues plan to use wearable technology to monitor heart rate variability in everyday life.
“Advances in wearable technology now enable real-time heart rate variability monitoring, allowing us to conduct ecological momentary studies that capture cardiovascular responses to social stress in naturalistic settings,” Yu said. “Such research promises to provide deeper insights into how loneliness impacts cardiovascular health in everyday life.”
“Although this is only an experimental study that preliminarily reveals the underlying mechanisms linking loneliness and cardiovascular health, accumulated evidence indicates that loneliness and social isolation significantly increase the risk of heart attack, stroke, and even early death,” he added. “As a member of the WHO Advisory Group on Social Connection, I would like to appeal to the public to recognize that reducing loneliness by fostering social connections is far more important for both physical and mental health than previously thought.”
The study, “(https://doi.org/10.1016/j.biopsycho.2024.108963) Loneliness is associated with diminished heart rate variability reactivity to acute social stress in younger adults,” was authored by Yunlong Song, Zhengqi Sun, Fengping Luo, and Bin Yu.

(https://www.psypost.org/new-study-links-coercive-food-practices-to-emotional-overeating-in-preschoolers/) New study links coercive food practices to emotional overeating in preschoolers
Dec 28th 2024, 16:00

A study published in (https://www.sciencedirect.com/science/article/abs/pii/S0195666324004112) Appetite sheds light on the potential impact of parenting practices involving food on children’s emotional and eating behaviors. Researchers at the University of North Florida found that coercive food practices are associated with poorer emotional regulation in preschoolers, which in turn is linked to emotional overeating.
The preschool years are a formative time for both emotional regulation and eating habits, as children develop greater autonomy and begin interacting more with peers. Emotional overeating—eating in response to negative emotions like stress or frustration—is known to be associated with unhealthy eating patterns, weight issues, and potential eating disorders later in life. Previous studies have suggested that coercive feeding practices, such as using food to manage behavior or emotions, may encourage emotional overeating. However, the mechanisms underlying this relationship remain unclear.
The new study aimed to explore whether these feeding practices are linked to emotional overeating through their impact on children’s ability to regulate their emotions. Additionally, the researchers sought to determine if these practices were similarly linked to emotional undereating, which is often considered a more natural stress response in young children.
The study involved 221 mothers of four- and five-year-old children recruited through online platforms Amazon Mechanical Turk and Prolific. Participants completed surveys assessing their feeding practices, their child’s emotional regulation abilities, and the child’s emotional eating behaviors. Only mothers were included to maintain consistency, as mothers are often primary caregivers and may differ from fathers in their feeding approaches.
The researchers assessed four coercive food practices:

Using food to regulate emotions: Offering food to calm or comfort a child when upset.
Using food as a reward: Providing food as a reward for desired behavior or withholding it as a punishment.
Emotional feeding: Offering food during emotionally charged situations regardless of hunger.
Instrumental feeding: Using food to encourage or discourage specific behaviors.

Children’s emotional regulation was measured using a validated checklist that assessed their ability to manage the intensity, duration, and expression of emotions. Emotional overeating and undereating were assessed through a questionnaire examining how often children ate more or less than usual in response to emotions.
The researchers found that all four coercive food practices were associated with poorer emotional regulation in children. Poor emotional regulation, in turn, was linked to increased emotional overeating. These findings support the idea that using food as a tool to manage emotions may teach children to rely on eating as a coping mechanism instead of developing more adaptive strategies for managing their feelings.
Interestingly, while coercive food practices were also linked to emotional undereating, this relationship was not mediated by emotional regulation. This suggests that emotional undereating is less influenced by learned behaviors from parents and may instead stem from biological stress responses.
The researchers also controlled for general food responsiveness—children’s tendency to eat in response to external food cues like the sight or smell of food. Even after accounting for this factor, emotional regulation remained a significant mediator, indicating that the connection between parenting practices and emotional overeating was not simply due to a general desire for food but was specifically tied to emotional coping strategies.
Although the findings highlight important links between parenting practices, emotional regulation, and eating behaviors, the study has some limitations. First, it relied on self-reported data from mothers, which may not always accurately reflect actual behaviors. Observational studies could provide a more objective view of parent-child interactions related to feeding and emotion regulation.
Additionally, the study was cross-sectional, meaning it captured a single point in time rather than changes over time. Longitudinal research is needed to determine whether coercive feeding practices lead to poorer emotional regulation and emotional overeating, or whether these behaviors influence each other in a reciprocal way. Future studies could also investigate the role of fathers and other caregivers in shaping children’s emotional and eating behaviors.
The study, “(https://doi.org/10.1016/j.appet.2024.107608) Parent’s use of coercive control practices with food is associated with poorer emotion regulation and increased emotional overeating in preschoolers,” was authored by Lindsay N. Baker and Anita J. Fuglestad.

(https://www.psypost.org/could-a-rare-gene-delay-alzheimers-apoe3-christchurch-inspires-hope-for-future-therapies/) Could a rare gene delay Alzheimer’s? APOE3 Christchurch inspires hope for future therapies
Dec 28th 2024, 14:00

Researchers have uncovered promising insights into Alzheimer’s disease through a study focusing on a Colombian family with a high genetic risk for early-onset Alzheimer’s. A rare genetic variant known as APOE3 Christchurch (APOE3Ch), found in members of this family, appears to delay the onset of cognitive decline. While a previous case study showed that carrying two copies of this variant resulted in remarkable resilience to the disease, the new study suggests that even one copy of the variant provides some protection. These findings, published in (https://www.nejm.org/doi/10.1056/NEJMoa2308583) The New England Journal of Medicine, offer new directions for understanding and potentially treating Alzheimer’s disease.
“As a clinician, I am highly encouraged by our findings, as they suggest the potential for delaying cognitive decline and dementia in older individuals. Now we must leverage this new knowledge to develop effective treatments for dementia prevention,” said co-first author Yakeel T. Quiroz, a clinical neuropsychologist and neuroimaging researcher and director of the Familial Dementia Neuroimaging Lab in the Departments of Psychiatry and Neurology at Massachusetts General Hospital.
“As a neuroscientist, I’m thrilled by our findings because they underscore the complex relationship between APOE and a deterministic mutation for Alzheimer’s disease, potentially paving the way for innovative treatment approaches for Alzheimer’s disease, including targeting APOE-related pathways.”
The study stemmed from a compelling medical mystery identified in 2019. Researchers reported a unique case of a woman who remained cognitively healthy until her late 70s, despite having a genetic predisposition to Alzheimer’s due to the Paisa mutation in the PSEN1 gene. This mutation nearly guarantees early-onset Alzheimer’s, typically manifesting in the mid-40s.
The woman’s resilience was linked to her carrying two copies of the APOE3 Christchurch variant. Inspired by this exceptional case, researchers aimed to investigate whether carrying just one copy of the APOE3Ch variant could also confer protection against Alzheimer’s in her extended family, which includes approximately 6,000 relatives and 1,200 carriers of the Paisa mutation.
The researchers conducted an analysis involving 1,077 members of the Colombian family with the PSEN1 mutation. Among them, they identified 27 individuals who carried one copy of the APOE3Ch variant. These participants underwent rigorous cognitive testing, neuroimaging, and, in some cases, postmortem brain analysis.
Using tools like the Functional Assessment Staging (FAST) system and the Mini-Mental State Examination (MMSE), the researchers assessed the participants’ cognitive status over time. To minimize bias, the study was conducted with a matched sample design, ensuring comparisons were controlled for variables like sex, education, and other genetic factors.
Individuals with one copy of the APOE3Ch variant experienced a delay of several years in the onset of mild cognitive impairment and dementia compared to those without the variant. Specifically, the median age at the onset of mild cognitive impairment was 52 years for carriers of the APOE3Ch variant, compared to 47 years for non-carriers.
Similarly, the median age for developing dementia was 54 years for carriers, while it was 50 years for non-carriers. While these delays were not as dramatic as those observed in the earlier case of a woman with two APOE3Ch copies, they nonetheless highlight the potential protective effects of the variant.
Further insights were gained through neuroimaging and pathological studies. Brain scans revealed that APOE3Ch carriers had a relatively limited accumulation of tau, a protein closely associated with Alzheimer’s pathology, despite a high burden of amyloid plaques. The reduced tau accumulation appeared to contribute to less neurodegeneration and better-preserved brain function. Postmortem analyses further supported these findings, showing that APOE3Ch carriers had less damage to cerebral blood vessels and a reduced presence of tau in critical brain regions.
Despite these promising findings, the researchers acknowledge several limitations. The study’s sample size for individuals with the APOE3Ch variant was relatively small, and all participants came from the same extended family, limiting the generalizability of the results. Additionally, the study focused on a rare form of Alzheimer’s caused by a specific genetic mutation, which may not fully translate to the more common, sporadic forms of the disease. Future research with larger, more diverse populations will be necessary to confirm these results and explore their broader implications.
Building on this work, the research team plans to further investigate the resilience seen in APOE3Ch carriers. This involves advanced brain imaging, cognitive testing, and biomarker analysis to identify the specific molecular and physiological factors at play.
“As a next step, we are currently focused on improving our understanding of the brain resilience among the remaining family members who carry one copy of the Christchurch variant. This involves conducting structural and functional MRI scans and cognitive evaluations, as well as analyzing blood samples to assess their protein and biomarker profiles,” said Quiroz. “The unwavering commitment to research shown by our Colombian patients with autosomal dominant Alzheimer’s and their families has been indispensable in making this study possible and allowing us to continue to work toward interventions for this devastating disease.”
The study, “(https://doi.org/10.1056/nejmoa2308583) APOE3 Christchurch Heterozygosity and Autosomal Dominant Alzheimer’s Disease,” was authored by Yakeel T. Quiroz, David Aguillon, Daniel C. Aguirre-Acevedo, Daniel Vasquez, Yesica Zuluaga, Ana Y. Baena, Lucia Madrigal, Liliana Hincapié, Justin S. Sanchez, Stephanie Langella, Rafael Posada-Duque, Jessica L. Littau, Nelson D. Villalba-Moreno, Clara Vila-Castelar, Liliana Ramirez Gomez, Gloria Garcia, Elizabeth Kaplan, Sofia Rassi Vargas, J. Alejandro Ossa, Pablo Valderrama-Carmona, Paula Perez-Corredor, Susanne Krasemann, Markus Glatzel, Kenneth S. Kosik, Keith Johnson, Reisa A. Sperling, Eric M. Reiman, Diego Sepulveda-Falla, Francisco Lopera, and Joseph F. Arboleda-Velasquez.

(https://www.psypost.org/prenatal-exposure-to-high-fluoride-concentrations-linked-to-lower-iq-in-children-study-finds/) Prenatal exposure to high fluoride concentrations linked to lower IQ in children, study finds
Dec 28th 2024, 12:00

An analysis of data from studies conducted in Denmark, Mexico, and Canada found that prenatal exposure to high concentrations of fluoride is associated with lower IQ scores in children at age 7. However, this association depended on the dose. In the low-exposure Danish sample, no association was found. A concentration of 0.3 mg/L of fluoride ions in maternal urine appears to be the critical threshold above which fluoride exposure begins to have toxic effects on children’s cognitive development. The research was published in the (https://doi.org/10.1093/eurpub/ckad170) European Journal of Public Health.
Fluorides are naturally occurring minerals found in water, soil, plants, and air, containing the element fluorine. These include compounds such as sodium fluoride, fluorosilicic acid, and sodium fluorosilicate. When dissolved in water, these minerals release fluoride ions that inhibit bacterial growth. They also help prevent tooth decay by strengthening tooth enamel and promoting remineralization. For this reason, fluorides are commonly used in toothpastes and mouth rinses to prevent cavities. In some countries, they are also added to public water supplies through a process called fluoridation.
Common dietary sources of fluoride, include tea and seafood. The fluoride concentration in tea can range from 1 to 6 mg/L depending on the type of tea and brewing method. Seafood, particularly fish eaten with bones (like sardines) and shellfish, also contains notable amounts of fluoride. Fruits and vegetables grown in regions with fluoride-rich groundwater can also contribute to fluoride intake.
At appropriate levels, fluoride is beneficial for oral health and significantly reduces the risk of tooth decay. However, excessive fluoride exposure, particularly during early childhood, can lead to dental fluorosis, a condition that causes discoloration or pitting of tooth enamel. Prolonged high intake may result in skeletal fluorosis, a condition that weakens bones and joints. Emerging research also suggests that exposure to high concentrations of fluoride can be toxic to children’s neurons during development. Elemental fluorine itself is highly toxic and chemically reactive, but it is rarely found in nature.
Study author Philippe Grandjean and his colleagues sought to examine the association between prenatal fluoride exposure and cognitive performance at school age. They analyzed data from a Danish study called the Odense Child Cohort (OCC) and combined it with similar datasets from Mexico and Canada.
The Odense Child Cohort is a longitudinal research study in Denmark investigating the health, development, and environmental exposures of children from prenatal stages through childhood to understand factors influencing long-term well-being. This cohort included pregnant women residing in the Odense municipality in Denmark between 2010 and 2012. For this analysis, the researchers focused on 837 singleton mother-child pairs, where data on the child’s cognitive performance at age 7 and maternal urine fluoride levels during pregnancy were available.
Water fluoridation is not legal in Denmark, but elevated fluoride levels naturally occur in groundwater in some parts of the country. In Odense, the fluoride concentration in drinking water is generally around 0.2–0.3 mg/L, which is considered low. The study authors combined the Odense data with data from similar studies in Mexico and Canada, where water fluoridation is common and exposure to fluoride during pregnancy is generally higher.
Fluoride exposure in this study was assessed by measuring fluoride ions in maternal urine samples collected during pregnancy. In the Odense study, children’s cognitive performance was assessed at age 7 using the Wechsler Intelligence Scales for Children. In the Mexican and Canadian datasets, cognitive assessments were conducted at comparable ages using different, yet equivalent, scales that generate IQ scores.
Results showed that in the Odense cohort, urine fluoride concentrations ranged from 0.08 to 3.04 mg/L, with a median of 0.52 mg/L. These values reflect generally low exposure levels compared to the North American cohorts, where fluoride concentrations were higher due to water fluoridation practices. In the Odense group, no statistically significant association was found between maternal fluoride concentrations during pregnancy and children’s cognitive performance at age 7, as measured by IQ tests. This suggests that at lower fluoride exposure levels, as observed in Denmark, the potential neurotoxic effects may not manifest.
However, when data from Mexico and Canada were combined with the Odense data, a different pattern emerged. The combined results demonstrated a weak but statistically significant negative association between higher prenatal fluoride exposure and children’s cognitive performance. Specifically, a maternal urine fluoride level increase of 1 mg/L was associated with a 2.06-point IQ decrease in children.
Further analysis revealed a potential threshold effect, with maternal urine fluoride concentrations of approximately 0.3 mg/L representing a critical level. Above this threshold, the likelihood of fluoride exposure having neurotoxic effects on children’s developing brains increased.
“The present study contributes new information on the weak association between fairly low levels of prenatal fluoride exposure and cognitive function at school age in a Danish birth cohort. A possible negative association could not be confirmed within the exposures measured in the OCC [Odense Child Cohort]. When merged with data from two previous prospective studies at higher exposures, a revised BMCL [benchmark concentration lower confidence limit] fluoride concentration of about 0.3 mg/l in maternal pregnancy urine suggests that elevated fluoride intakes, whether from drinking water, black tea, or other sources, during pregnancy may require public health attention,” the study authors concluded.
The study contributes to the scientific understanding of the effects of fluorides on brain development. However, fluoride exposure was measured at a single point during pregnancy, which may not accurately represent cumulative exposure over the entire gestation period. While the findings demonstrate an association between higher prenatal fluoride exposure and lower IQ in children, they do not establish a direct causal relationship.
The analysis adjusted for many control variables (e.g., parental education, gestational age, breastfeeding), but the observational nature of the study means that other unmeasured factors, such as nutritional deficiencies or exposure to other environmental neurotoxicants, could contribute to the observed cognitive effects.
The paper, “(https://doi.org/10.1093/eurpub/ckad170) Dose dependence of prenatal fluoride exposure associations with cognitive performance at school age in three prospective studies,” was authored by Philippe Grandjean, Alessandra Meddis, Flemming Nielsen, Iben H. Beck, Niels Bilenberg, Carly V. Goodman, Howard Hu, Christine Till, and Esben Budtz-Jørgensen.

(https://www.psypost.org/similarity-attraction-proves-to-be-a-surprisingly-unshakable-psychological-effect/) Similarity-attraction proves to be a surprisingly unshakable psychological effect
Dec 28th 2024, 10:00

A new study published in (https://doi.org/10.1080/00224545.2024.2427834) The Journal of Social Psychology confirms that individuals prefer closer connections with those they perceive as more similar to themselves, even in contexts that emphasize intergroup differences. The research examined attitudes among ethnic, religious, and political groups and found that similarity-attraction theory remains robust regardless of whether diversity or shared traits are celebrated. These findings contribute to our understanding of intergroup relations in increasingly diverse societies.
The study aimed to explore whether the well-established similarity-attraction theory, which suggests people are more drawn to those they perceive as similar, holds true in intergroup settings. While much of the previous research on this topic has focused on interpersonal relationships, the researchers recognized a gap in understanding how this dynamic operates between groups, particularly in modern, diverse societies where multiculturalism often highlights intergroup differences.
“The first issue that inspired the research topic is that many contemporary societies are experiencing increasing diversity,” said study author (https://orcid.org/0000-0002-9427-455X) Raimundo Salas-Schweikart, a magister in public policy and PhD candidate in psychology at Georgetown University.
“In this regard, there has been a lot of research on diversity from a multicultural perspective. In general terms, this research has validated diverse identities, and rightly so. However, this research agenda has neglected that, as human beings, we share several commonalities. Similarity-attraction theory provides a perspective to investigate how the perception of similarities can lead to engaging with different others.”
The researchers conducted four studies, each focusing on a specific group context. Across the studies, a total of 2,664 participants were recruited via an online research platform.
In the first study, the researchers examined the relationship between perceived similarity and desired social closeness among three major ethnic groups in the United States: Black, Hispanic, and White Americans. A total of 231 participants (43% female, average age 34.86 years) were recruited through Prolific Academic. The recruitment criteria included self-identification with one of the three target ethnic groups, residence in the United States, and a balance of political ideologies.
Participants were asked to complete two measures. The first was the Perceived Similarity Index (PSI), which evaluated how similar participants perceived themselves to be to members of an ethnic outgroup across seven dimensions, such as values, culture, and trustworthiness. The second measure, adapted from the Social Distance scale, assessed participants’ willingness to engage with members of the outgroup in scenarios such as becoming friends, neighbors, or colleagues.
Participants were randomly assigned to evaluate one of the other two ethnic groups as the target outgroup. For example, Black participants assessed either Hispanic or White Americans. The study included demographic and political orientation questions to control for these variables in the analysis.
Across Black, Hispanic, and White Americans, participants consistently expressed a desire for closer social relationships with outgroups they perceived as more similar. This pattern held regardless of whether the emphasis was on similarities, differences, or neither.
Study 2 built on the findings of Study 1 by incorporating three experimental conditions: a control condition, a “celebration of differences” condition, and a “celebration of similarities” condition. A larger sample of 823 participants (48% female, average age 30.17 years) was recruited, with the same ethnic group stratification and recruitment procedures as in Study 1.
Participants were randomly assigned to one of the three conditions. In the celebration of differences condition, they read a prompt emphasizing the unique qualities of ethnic groups. In the celebration of similarities condition, the prompt highlighted shared traits among ethnic groups. The control condition provided no framing related to intergroup differences or similarities. As in Study 1, participants completed the PSI and Social Distance measures, evaluating their perceptions and willingness to engage with one of the other two ethnic groups.
The researchers found that the experimental conditions had no significant effect on the relationship between perceived similarity and desired social closeness. Participants in all three conditions consistently showed a preference for closer contact with outgroups they perceived as more similar to themselves.
Importantly, the results replicated the findings from Study 1 with a larger and more diverse sample, reinforcing the robustness of the similarity-attraction paradigm in ethnic intergroup contexts.
Study 3 shifted focus to religious groups, specifically Baptists, Catholics, and Protestants in the United States. A total of 1,004 participants (68% female, average age 37.75 years) were recruited using the same platform and methods as the previous studies. Participants were required to self-identify with one of the three Christian denominations, and recruitment ensured an even distribution across these groups.
The experimental setup mirrored that of Study 2, with participants assigned to the control condition, the celebration of differences condition (highlighting distinctiveness among religious groups), or the celebration of similarities condition (emphasizing commonalities among religious groups). Participants completed the PSI and Social Distance measures, this time evaluating members of one of the other two religious groups.
Across all conditions, the researchers found a consistent negative relationship between perceived similarity and social distance. Participants from all three denominations expressed a preference for closer contact with members of religious outgroups they perceived as more similar to their own group.
Unlike in Study 2, there was a small but notable finding in the celebration of similarities condition for Baptists. Participants in this condition showed an even stronger preference for social closeness with similar others, suggesting that emphasizing commonalities may slightly amplify the effect of similarity-attraction in certain religious contexts. However, this was not observed for Catholics or Protestants.
The fourth study examined the similarity-attraction dynamic within the realm of political ideology. A total of 606 participants (48% female, average age 42.69 years) were recruited, split evenly between self-identified liberals and conservatives. Recruitment criteria included residence in the United States and affiliation with one of the two political orientations.
As in Study 2 and Study 3, participants were randomly assigned to one of three experimental conditions. In the celebration of differences condition, participants read a prompt emphasizing the value of ideological diversity and the distinctiveness of political groups. In the celebration of similarities condition, the prompt highlighted shared values and common goals across the political spectrum. The control condition provided no such framing. Participants completed the PSI and Social Distance measures, evaluating members of the opposing political orientation.
Consistent with the previous studies, the researchers found a robust negative relationship between perceived similarity and social distance. Participants from both political orientations preferred closer contact with outgroup members they perceived as ideologically similar, regardless of whether the experimental condition emphasized differences, similarities, or neither.
The experimental conditions had no significant effect on the similarity-attraction relationship, suggesting that political preferences for similarity are resistant to external framing. This finding is particularly significant given the polarized nature of political discourse in the United States. The results demonstrated that even in a divisive political landscape, people’s preferences for similar others remain stable across ideological lines.
“The strength of perceived similarities was unexpectedly robust,” Salas-Schweikart told PsyPost. “Moreover, it was surprising to find it across political groups since they highlight the differences more than the similarities.”
He highlighted two key takeaways from the findings: “First, the strength and importance of similarities. Across different types of groups (e.g., ethnic, political, religious), similarity predicted closer relations with members of different groups.
“Second, and as a consequence of the first one, given the ubiquitous nature of similarity among groups and its importance in predicting how close the groups are, policymakers could consider similarity attraction when designing policies for the current diverse societies.”
The research highlights that perceived similarity strongly influences preferences for social closeness with outgroup members. But as with all research, there are limitations.
“One important caveat we need to consider is that we used a U.S.-based sample across our studies,” Salas-Schweikart noted. “Samples from other places may yield different outcomes. Therefore, more research is required to explore whether and how similarity-attraction theory holds in non-WEIRD populations.”
Future research could also explore strategies to effectively reduce intergroup bias by leveraging shared identities or examining how similarity-attraction might interact with other factors like group status or cultural norms.
“An important long-term goal is to contribute to the cohesion of diverse societies,” Salas-Schweikart said. “One challenge of diversity is common ground to constitute open and inclusive societies.”
“If the reader wants to explore more about the significance of similarity attraction and the challenge of diversity, they can refer to (https://amzn.to/4iXAUyD) The Psychology of Multiculturalism, Assimilation, and Omniculturalism: Managing Diversity in Global Context, by one of the paper authors, Prof. Moghaddam,” he added.
The study, “(https://doi.org/10.1080/00224545.2024.2427834) Similarity-attraction across ethnic, religious, and political groups: does celebrating differences or similarities make a difference?“, was authored by Raimundo Salas-Schweikart, Margaret J. Hendricks, Melanie Boychuck, and Fathali M. Moghaddam.

Forwarded by:
Michael Reeder LCPC
Baltimore, MD

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