Does fluoride exposure affect thyroid function? A systematic review and dose-response meta-analysis

Effects of Selenium Administration on Blood Lipids: A Systematic Review and Dose-Response Meta-Analysis of Experimental Human Studies

CONTEXT

Overexposure to the essential trace element selenium has been associated with adverse metabolic and cardiovascular outcomes, hypertension, and diabetes. However, dose-response meta-analyses analyzing the effects of selenium administration on the lipid profile in experimental human studies are lacking.

OBJECTIVE

Through a restricted cubic spline regression meta-analysis, the dose-response relation between the dose of selenium administered or blood selenium concentrations at the end of the trials and changes over time in blood lipids, ie, total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides was assessed.

DATA SOURCES

Searches were performed on PubMed, Web of Science, Embase, and the Cochrane Library from inception up to January 11, 2025 to identify randomized controlled trials (RCTs) investigating the impact of selenium supplementation on blood lipid profiles among adults.

DATA EXTRACTION

A total of 27 eligible RCTs that enrolled healthy individuals, pregnant individuals, and participants with specific health conditions were identified and the relevant data was extracted.

DATA ANALYSIS

Dose-response analysis indicated that selenium administration at and above 200 µg/day decreased HDL and LDL cholesterol and increased triglyceride levels. Blood selenium concentrations at the end of the trial above approximately 150 µg/L were positively associated with triglyceride and LDL cholesterol concentrations, and inversely associated with HDL cholesterol. Inorganic selenium supplementation showed stronger associations than organic selenium. At the lowest levels of baseline intake, selenium supplementation appeared instead to have beneficial effects on the lipid profile, with an overall indication of U-shaped curves, apart from HDL-cholesterol. The adverse effects of selenium were stronger in studies involving healthy participants as compared with unhealthy participants and pregnant females, in those having a longer duration of the intervention, particularly more than 3 months, and in European populations at selenium intake levels of above 300 µg/day.

CONCLUSIONS

In this dose-response meta-analysis of experimental human studies, an adverse effect of selenium administration on blood lipids at levels around or above the current upper level of intake was observed.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration No. CRD42022380432.

Calling for a comprehensive risk assessment of selenium in drinking water

In the last two decades, research has elucidated that selenium, a trace element, has both nutritional and toxicological effects on human health, depending on its dose and chemical form. Recent animal, laboratory, and human studies have shown harmful effects of certain selenium species at specific exposure levels, prompting the need to reassess overall exposure to this element, including that occurring through drinking water, a primary source of inorganic selenium. Drinking water selenium standards worldwide are scarce and existing standards are inconsistent, likely because they have been informed by an incomplete and outdated assessment of the scientific evidence. Incorporating all the available human and laboratory evidence into a precautionary regulatory framework indicates that a drinking water limit of around 5 μg/L of selenium is needed to protect human health, i.e. with an uncertainty factor of 2 versus the lowest adverse effect level observed in human studies, and that higher values may pose unacceptable risks to humans. Despite the rarity of such high levels of selenium in underground and potable waters, coal mining and other sources of environmental pollution as well as geological factors may raise drinking water selenium content above a safe threshold, triggering the need to protect consumers, and to face challenging technological issues for selenium removal, currently under active investigation.

Association between fluoride exposure and the risk of serum CK and CK-MB elevation in adults: a cross-sectional study in China

Background

This study aimed to investigate the relationship between urinary fluoride concentration and myocardial disease.

Methods

This is a cross-sectional study that was conducted in three villages in Wenshui County, Shanxi Province. A total of 737 villagers were included in this analysis. Urinary fluoride was detected using a fluoride-ion selective electrode. Myocardial enzymes were detected using an automatic biochemical analyzer. Myocardial ischemia and arrhythmia were diagnosed using 12-lead electrocardiogram.

Results

The median level of urinary fluoride concentration was 1.32 mg/L. Urinary fluoride was associated with serum creatine kinase (CK) elevation (odds ratio [OR] = 1.39 [95% confidence interval (CI)]: 1.09-1.78) and CK isoenzyme (CK-MB) elevation (OR = 1.49 [95% CI: 1.12-1.97]). Stratified analysis revealed that urinary fluoride concentration was associated with CK elevation in villagers under the age of 60 years (OR = 1.80 [95% CI: 1.26-2.59]). This study found that there was a positive association between urinary fluoride concentration and the risk of CK-MB elevation in participants under the age of 60 years(OR = 2.18 [95% CI: 1.39-3.42]), those who were of female gender (OR = 1.53 [95% CI: 1.07-2.19]), those who were overweight/obese (OR = 1.96 [95% CI: 1.28-2.99]), those who had central obesity (OR = 1.59 [95% CI: 1.12-2.25]), consumed alcohol (OR = 1.49 [95% CI: 1.09-2.05]), and smoked (OR = 1.50 [95% CI: 1.10-2.04]).

Conclusion

Our study suggests that fluoride exposure is associated with the risk of serum CK and CK-MB elevation; however, it is not associated with myocardial ischemia, arrhythmia, serum lactate dehydrogenase (LDH), serum alpha-hydroxybutyrate dehydrogenase (α-HBD), or serum aspartate aminotransferase (AST). Further investigations are needed to substantiate our findings and explore the potential underlying mechanisms.

Cadmium exposure and risk of hypertension: A systematic review and dose-response meta-analysis

BACKGROUND

Exposure to environmental toxic metals represents a significant global public health concern. Many studies have reported that cadmium (Cd) exposure increases the risk of hypertension. Since the shape of such relation has not been well characterized, we assessed it by performing a systematic review and dose-response meta-analysis of human studies.

METHODS

We searched the literature through September 5, 2024 to identify papers related to Cd, hypertension, and blood pressure. Inclusion criteria were: observational design, adult population, assessment of exposure using Cd biomarkers, and availability of exposure category-specific risk estimates for hypertension. We performed a dose-response meta-analysis of the results from included studies.

RESULTS

Of the 18 studies published between 2006 and 2024, most had a cross-sectional design. Cd was measured in whole blood and/or urine in almost all studies, whereas only two studies measured Cd in serum. The dose-response meta-analysis indicated an almost linear relation between urinary Cd concentrations and hypertension risk with RR = 1.18, 95% CI 1.02-1.37 at 2.0 μg/g creatinine compared with no exposure. In contrast, the association between blood Cd concentrations and hypertension risk was non-linear: there was a steep monotonic increase in risk for Cd concentrations below 2 μg/L, reaching a RR of 1.48 (95% CI 1.17-1.86) at 2.0 μg/L, after which a plateau seemed reached. We found similar trends when restricting to studies of Asian population, while when considering North American studies, hypertension risk increased above 1.0 μg/g creatinine.

CONCLUSIONS

In this dose-response meta-analysis, risk of hypertension showed a non-linear positive association with blood Cd concentrations and a linear positive association with urinary Cd concentrations. Inconsistency in the shape of associations could relate to the different timing of exposure assessed by the biomarkers or the alteration Cd excretion at increasing exposure levels. Mitigation of Cd exposure is confirmed as a public health priority for chronic disease prevention.

Association of fluoride exposure with disease burden and neurodevelopment outcomes in children in South Korea

BACKGROUND

Community water fluoridation is an effective public health strategy for preventing dental caries, yet. Concerns exist about potential health problems. This study explores associations between tap water fluoride levels and pediatric disease burden, as well as neurodevelopmental outcomes at 6 years of age.

METHODS

This nationwide population-based cohort study included children born in Korean cities with and without tap water fluoridation projects, between 2006 and 2012, aiming for a fluoride concentration of 0.8 ± 0.2 mg/L in treated tap water. Data from the National Health Insurance Service were used, spanning from birth to 2018. The relationship between exposure to fluoridated tap water and incidence of 16 childhood diseases that were previously identified as potentially linked to fluoride exposure were examined. Additionally, we evaluated the neurodevelopmental outcomes across various domains, including gross motor, fine motor, cognition, language, social skills, and self-help functions. These assessments were performed using data from a comprehensive national health screening program for children aged six years.

RESULTS

A fluoride-unexposed group included 22,881 children, whereas a fluoride-exposed group comprised 29,991 children (52% males). Children in the fluoride-exposed group had a decreased risk of dental caries and bone fractures [hazard ratio (95% confidence interval, CI), 0.76 (0.63-0.93) and 0.89 (0.82-0.93), respectively] and increased risk of hepatic failures [1.85, (1.14-2.98)] compared to those in the unexposed group. Additionally, the risk ratio of abnormal neurodevelopmental screening outcomes increased by 9%, but this was statistically uncertain (95% CI, 0.95-1.26).

CONCLUSIONS

Fluoridated tap water was associated with an increased risk of hepatic failure but a decreased risk of bone fractures in children. The association between fluoridated tap water and neurodevelopmental screening outcomes at 6 years remains unclear, highlighting the need for further studies to clarify this association.

Gut microbiome and function are altered for individuals living in high fluoride concentration areas in Pakistan

BACKGROUND

Endemic fluorosis refers to the condition when individuals are exposed to excessive amounts of fluoride ion due to living in a region characterized by elevated levels of fluorine in the drinking water, food, and/or air. In Pakistan, a substantial proportion of the population is thereby affected, posing a public health concern.

OBJECTIVES

Assessing how the gut microbiota and its metabolic profiles are impacted by chronic exposure to fluoride in drinking water (that caused Dental Fluorosis) as well as to perceive how this microbiota is connected to adverse health outcomes prevailing with fluoride exposure.

METHODS

Drinking water (n=27) and biological samples (n=100) of blood, urine and feces were collected from 70 high fluoride exposed (with Dental Fluorosis) and 30 healthy control (without Dental Fluorosis) subjects. Water and urinary fluoride concentrations were determined. Serum/plasma biochemical testing was performed. Fecal DNA extraction, 16S rRNA analysis of microbial taxa, their predicted metabolic function and fecal short chain fatty acids (SCFAs) quantification were carried out.

RESULTS

The study revealed that microbiota taxonomic shifts and their metabolic characterization had been linked to certain host clinical parameters under the chronic fluoride exposure. Some sets of genera showed strong specificity to water and urine fluoride concentrations, Relative Fat Mass index and SCFAs. The SCFAs response in fluoride-exposed samples was observed to be correlated with bacterial taxa that could contribute to adverse health effects.

CONCLUSIONS

Microbial dysbiosis as a result of endemic fluorosis exhibits a structure that is associated with risk of metabolic deregulation and is implicated in various diseases. Our results may form the development of novel interventions and may have utility in diagnosis and monitoring.

Ozone therapy in dentistry: An overview of the biological mechanisms involved (Review)

At low medically-relevant concentrations, ozone serves as an oxidant with a wide spectrum of antimicrobial activity and the ability to promote healing and reduce inflammation. Despite providing therapeutic benefits in a range of diseases, certain adverse effects and contraindications of ozone treatment must be considered. These are primarily related to toxicity from inhalation and systemic types of administration and can be avoided by following relevant guidelines and recommendations. Ozone therapy has been implemented in a number of fields of dentistry and the most commonly used formulations for the oral cavity are gaseous ozone, ozonized water and ozonized oil. The biological mechanisms underlying the molecular effects of ozone have been increasingly reported, but currently remain largely unknown. The aim of the present review was to provide an overview of the mechanisms involved in ozone interaction with dental tissues. The present review focused on relevant evidence regarding the effect of ozone on dental tissues, including periodontal structures, dental cells, enamel and dentine, considering in vitro studies in addition to animal and human studies. A variety of biological mechanisms acting through multiple biochemical target pathways were reported to be responsible for the therapeutic effects of ozone. The main beneficial effects of ozone occurred in the following domains: antimicrobial activity, remineralization and microstructural changes of hard dental tissues, immunomodulation and biostimulation of dental and periodontal cells. Additional research could provide further insights into the use of ozone, increase its use for broader clinical applications and assist in the selection of targeted protocols.

Alcohol Intake and Risk of Hypertension: A Systematic Review and Dose-Response Meta-Analysis of Nonexperimental Cohort Studies

BACKGROUND

Alcohol consumption has been associated with higher blood pressure and an increased risk of hypertension. However, the possible exposure thresholds and effect-modifiers are uncertain.

METHODS

We assessed the dose-response relationship between usual alcohol intake and hypertension incidence in nonexperimental cohort studies. After performing a systematic literature search through February 20, 2024, we retrieved 23 eligible studies. We computed risk ratios and 95% CI of hypertension incidence using a nonlinear meta-analytic model based on restricted cubic splines, to assess the dose-response association with alcohol consumption.

RESULTS

We observed a positive and almost linear association between alcohol intake and hypertension risk with risk ratios of 0.89 (0.84-0.94), 1.11 (1.07-1.15), 1.22 (1.14-1.30), and 1.33 (1.18-1.49) for 0, 24, 36 and 48 g/d, respectively, using 12 g alcohol/d as the reference value. In sex-specific analyses, the association was almost linear in men over the entire range of exposure but only observed above 12 g/d in women, although with a steeper association at high levels of consumption compared with men. The increased risk of hypertension above 12 to 24 g alcohol/d was similar in Western and Asian populations and considerably greater in White than in Black populations, mainly due to the positive association in women at moderate-to-high intake.

CONCLUSIONS

Overall, our results lend support to a causal association between alcohol consumption and risk of hypertension, especially above an alcohol intake of 12 g/d, and are consistent with recommendations to avoid or limit alcohol intake. Sex and ethnicity appear to be major effect-modifiers of such association.

Ozone Treatment for the Management of Caries in Primary Dentition: A Systematic Review of Clinical Studies

Dental caries in children is a frequent and debilitating condition, whose management is often challenging. The aim of this systematic review was to investigate the effectiveness of ozone applications for the treatment of caries in primary dentition. According to PRISMA guidelines, a systematic literature search was performed up to 6 January 2024. Clinical studies using ozone to treat caries of deciduous teeth were considered for inclusion. Out of the 215 records retrieved, seven studies were eventually included in the review, all of which used gaseous ozone. Four studies were judged at high risk of bias, two at low risk, and one of some concerns. The great heterogeneity of designs, outcomes, and protocols made it impossible to conduct a meta-analysis. Despite some limitations, the evidence yielded by the included studies suggests that ozone application, regardless of the protocol applied, is comparable to other interventions in terms of clinical outcomes and anti-bacterial activity, with no reported adverse effects and good patient acceptance. Therefore, ozone application may be a non-invasive approach to treat caries in primary dentition, especially in very young and poorly cooperative patients. Further standardized and rigorous studies are, however, needed to identify the best clinical protocols for this specific field.

The Effect of Prenatal and Neonatal Fluoride Exposure to Morphine-Induced Neuroinflammation

Physical dependence is associated with the formation of neuroadaptive changes in the central nervous system (CNS), both at the molecular and cellular levels. Various studies have demonstrated the immunomodulatory and proinflammatory properties of morphine. The resulting neuroinflammation in drug dependence exacerbates substance abuse-related behaviors and increases morphine tolerance. Studies prove that fluoride exposure may also contribute to the development of neuroinflammation and neurodegenerative changes. Morphine addiction is a major social problem. Neuroinflammation increases tolerance to morphine, and neurodegenerative effects caused by fluoride in structures related to the development of dependence may impair the functioning of neuronal pathways, change the concentration of neurotransmitters, and cause memory and learning disorders, which implies this element influences the development of dependence. Therefore, our study aimed to evaluate the inflammatory state of selected brain structures in morphine-dependent rats pre-exposed to fluoride, including changes in cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) expression as well as microglial and astroglial activity via the evaluation of Iba1 and GFAP expression. We provide evidence that both morphine administration and fluoride exposure have an impact on the inflammatory response by altering the expression of COX-1, COX-2, ionized calcium-binding adapter molecule (Iba1), and glial fibrillary acidic protein (GFAP) in brain structures involved in dependence development, such as the prefrontal cortex, striatum, hippocampus, and cerebellum. We observed that the expression of COX-1 and COX-2 in morphine-dependent rats is influenced by prior fluoride exposure, and these changes vary depending on the specific brain region. Additionally, we observed active astrogliosis, as indicated by increased GFAP expression, in all brain structures of morphine-dependent rats, regardless of fluoride exposure. Furthermore, the effect of morphine on Iba1 expression varied across different brain regions, and fluoride pre-exposure may influence microglial activation. However, it remains unclear whether these changes are a result of the direct or indirect actions of morphine and fluoride on the factors analyzed.