Full Length ArticleIn utero exposure to fluoride and cognitive development delay in infants
Introduction
Fluorides are naturally-occurring components in rocks and soil and are also found in air, water, plants, and animals. The general population is exposed to fluoride (F) through the consumption of drinking water, foodstuff, and dental products. Populations living in areas with naturally high F levels in water and soil may be exposed to high levels of F in water, especially if drinking water is provided from wells (ATSDR, 2003, Vineet Dhar1, 2009). In the central and north areas of Mexico there are groundwater with elevated levels of F (Ortega-Guerrero, 2009). In this areas, almost 90% of the population has the practice of use tap water for food preparation and direct consumption as drinking water (Jarquín-Yañez et al., 2015). The bioavailability of F through ingestion 80–100% (ATSDR, 2003).
Epidemiological research conducted in school age children living in endemic hydrofluorosis areas have evaluated the influence of exposure of F on cognitive development assessed as intelligence quotient scores (IQ). Different intelligence tests have been used (RAVEN-Chinese version, Wechsler Intelligence Scales, Stanford-Binet Intelligence Scale) and have reported lower IQ points associated with F exposure at concentrations of 2.20–3.94 mg/l compared with residents from control areas (concentrations of F in water <0.41 mg/l). The lack of biomarkers of exposure and control of potential confounders is an issue that has to be considered in these studies (Karimzade et al., 2014, Trivedi et al., 2012). Other well conducted research papers also reported that F decreases IQ scores (Ding et al., 2011, Rocha-Amador et al., 2007).
Cognitive development alterations associated with F exposure could start in early prenatal stages of life and come up later at school age; and likely continue into adulthood. Few studies have explored this hypothesis and the evidence is inconclusive. For example, Chinese newborns; scored lower in the Standard Neonatal Behavioral Neurological Assessment (NBNA) test in the high exposure group (F in urine 3.58 ± 1.47) compared with the control group (1.74 ± 0.96 mg/l); 36.48 ± 1.09 vs 38.28 ± 1.10, p < 0.05, respectively (Li et al., 2008). Another study in aborted fetuses of mothers living in an endemic hydrofluorosis area (4.3 ± 2.9 mg/l of F in urine) reported changes in neurotransmitters compared with levels of aborted fetuses of mothers living in non-endemic areas (F in urine 1.67 ± 0.8 mg/l) (Yu et al., 2008). Regarding experimental studies, data shows that F accumulates in the brain, specifically in the hippocampus; a region associated with memory, attention and learning (Shivarajashankara et al., 2001, Bhatnagar et al., 2006, Basha et al., 2011). About gestational exposure, some experimental studies, indicated that F alters learning and memory (Mullenix et al., 1995, Bera et al., 2007, Basha et al., 2011).
In endemic hydrofluorosis areas millions of people consume contaminated water daily, including pregnant women and there is evidence that support the F capacity to cross the placental and the blood-brain barriers and accumulate in critical areas of the brain related to cognitive development. The objective of this research was to evaluate the influence of in utero exposure to F in Mexicans infants born from mothers living in endemic hydrofluorosis areas on the Mental and Psychomotor Development (MDI and PDI) through the Bayley Scale of Infant Development II (BSDI-II).
Section snippets
Participants and recruitment
Authorizations from the authorities of the Ministry of Health (SSA) of the selected municipalities included for the study were obtained. The project protocol was conducted in accordance with the Declaration of Helsinki and was approved by the bioethics committees of the SSA from the municipalities. Follow up was conducted in pregnant women recruited from 2013 to 2014 who received prenatal care in health centers located in Durango City and Lagos de Moreno, Jalisco, Mexico. Both are endemic
Results
Table 1 shows the comparison of general characteristics of the pregnant women between participants in the biological monitoring and the women who agreed to their child’s cognitive evaluation. The average age of the participants was 22.4 ± 4.0, in education 41.5% of the participants had completed high school. Regarding marital status, 69.7% of the participants were married, 70.7% of the participants reported being housewives, and for 44.6% of the participants it was their first birth. About
Discussion
The objective of this research was to evaluate the influence of in utero exposure to F on Mental and Psychomotor Development evaluated through the BSDI II in Mexican children born from mothers living in endemic hydrofluorosis areas. The proportion of children with values of MDI less than minus one standard deviation (SD) was 38.5%; scores under 85 points are considered as an indicator of possible developmental delay. This test evaluates psychological processes such as attention, memory, sensory
Conclusion
Due the importance of cognitive development in children and the amount of people (millions) exposed daily; more studies need to be conducted to support the in utero exposure of F and effects in young children. Considering previous data supporting the potential neurotoxicity of F in school-age children, preventive measures in affected communities should be implemented (communication programs, treatments water methods and a continuous monitoring to guarantee water quality) to decrease the F
Conflict of interest
None.
Acknowledgements
The authors acknowledge the financial support of this research by CONACYT with number 181577, FONSEC 2012 and the University of Guanajuato through DAIP support with number FO-DAI-05, 2013. The present work was carried out during the first period of the first author postdoctoral training (fellowship number 239404).
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2022, Environmental ResearchCitation Excerpt :Recent studies conducted in the United States (Abduweli Uyghurturk et al., 2020), Canada (Till et al., 2018), and Mexico (Thomas et al., 2016; Castiblanco-Rubio et al., 2021) have reported positive associations between fluoride from dietary sources, including drinking water and salt, and urinary fluoride levels in pregnant women. Because of its ubiquity and its ability to pass through the placenta and blood-brain barrier to reach the fetal brain (Agency for Toxic Substances and Disease Registry, 2003), the safety of fluoride exposure in pregnancy has received much attention, both in endemic fluorosis areas (Jiménez et al., 2017) and communities that have fluoridation programs (Green et al., 2019; Bashash et al., 2017). While it is not disputed that fluoride is a developmental neurotoxicant at high exposure levels, there are relatively few studies that have assessed fluoride's potential neurotoxicity at levels found in fluoridated areas (i.e., 0.7 mg/L), particularly for pregnant women and young infants.