Water contributes significantly to the physiological functions in the in the human body. However, low fluoride doses have been reported to affect the central nervous system (CNS) without first causing the physical malformations of dental and skeletal fluorosis. Aims and objectives were to determine fluoride concentrations in water used by adolescents who were born and raised in North Kajiado and correlated it with their Auditory Working Memory Index (AWMI). The survey was cross-sectional and descriptive involving 269 school children aged 13-15 years. A purposeful sampling frame was used to select the schools. Fluoride in water was determined using the Fluoride Ion selective electrode. The AWM was assessed using the Wechsler intelligence scale for Children V (WISC-V) subtest. The mean auditory working index for the group was 111.5±22.6 while the boys had a mean AWMI of 111.46±22.37 and the girls 111.56±22.75. A comparison of the AWM of children from low (105.40±23.6) and high (99.52±23.2) fluoride schools and medium with high fluoride school had significant differences. The AWM for the children whose household water had low fluoride had higher AWMI 122.58±19.9 compared to those whose household had high fluoride in the with ANOVA F (2, 266) = 17.968, p?.0001 and Tukey HSD for low and medium (m=-5.919, se=3.146, p=.145, low and high fluoride, (m=-18.559. se=3.124, p?.001; medium and high (m=-12.640, se= 3.32, p?.001 at 95% CL. In conclusion, low fluoride in the water seemed to enhance the AWM. However, the AWM declined with an increased in the fluoride concentration in water.
The current study found a higher proportion of children with high AWM in low household water fluoride than in high water fluoride areas. The finding in the current study is contrary to what a study in India reported higher fluoride levels resulted in higher levels of intelligence . Memory is defined merely as the ability to retain information over time. Auditory memory is the ability to take orally presented information, process it, store it and be able to recall what was heard . This cognitive functioning requires one to be attentive, record, process, store and retrieve the information when needed. Poor AWM results when children can’t record, process, store or retrieve the information that was exposed to, this has negative consequences on learning. Children with low AWL find it challenging to pay attention and follow instructions. AWM plays a critical role in literacy as it has a direct impact on reading and writing, spelling and mathematics skills. According to Cyndi Ringoean, a neuro-developmentalist, a child with poor AWM cannot learn using the phonics method . When even doing self-reading, listening and processing the information when the child needs to do silent reading a good AWM to recall what was read. Addie Cusimano also opines that AWM is overlooked as a learning skill deficiency and he found severe deficiencies in children with hyperactivity and or attention deficit disorders . Working memory is strongly correlated to intelligence in adults and children hence those performing better on working memory tasks have also shown a tendency to be better on the intelligence task  . Several animal studies have tried to explain the possible mechanisms of neurotoxicity of fluoride  . Fluoride when ingested through the child’s diet or crosses the placenta, its retained in the body about 80-90% in children and 60% in adults  . Its absorbed into the bloodstream and forms complexes which are lipid soluble and can cross the blood-brain- barrier hence accumulating in the cerebral tissues . This complexes then affect the development of the CNS by different mechanisms, e.g. inhibition of glutamate transporters, free radical generation and inhibition of mitochondrial energy and antioxidant enzymes . This alteration in the structure and function in the CNS especially during the 1st eight years of life and also during foetal growth may lead to cognitive dysfunction, intellectual deficits and learning difficulties  . Fluoride has also been shown to interfere with thyroid gland activity leading to an adverse effect on the development of the brain and function in children .