Decreased intelligence in children and exposure to fluoride and arsenic in drinking water


Rocha-Amador D, Navarro ME, Carrizales L, Morales R, Calderón J. Cad Saude Publica. 2007;23 Suppl 4:S579-87. (See study)

Arsenic is a common contaminant in the fluoridating chemicals added to drinking water, particularly hydrofluorosilicic acid. In NZ, authorities have argued that the arsenic becomes so dilute that it is not a health concern. However, because arsenic is a known carcinogen, and chronic exposure to any amount of a carcinogen will carry with it some cancer risk, the maximum containment goal for arsenic should be zero, in keeping with all other carcinogens. Arsenic and fluoride belong in a unique class of general poisons with a wide range of biological effects.


Recent evidence suggests that fluoride (F) and arsenic (As) may adversely affect intelligence quotient (IQ) scores. We explore the association between exposure to F and As in drinking water and intelligence in children. Three rural communities in Mexico with contrasting levels of F and As in drinking water were studied: Moctezuma (F 0.8+/-1.4 mg/L; As 5.8+/-1.3 microg/L); Salitral (F 5.3+/-0.9 mg/L; As 169+/-0.9 microg/L) and 5 de Febrero (F 9.4+/-0.9 mg/L; As 194+/-1.3 microg/L). The final study sample consisted of 132 children from 6 to 10 years old. After controlling for confounders, an inverse association was observed between F in urine and Performance, Verbal, and Full IQ scores (beta values = -13, -15.6, -16.9, respectively). Similar results were observed for F in drinking water (beta values = -6.7, -11.2, -10.2, respectively) and As in drinking water (beta values= -4.30, -6.40, -6.15, respectively). The p-values for all cases were < 0.001. A significant association was observed between As in urine and Full IQ scores (beta = -5.72, p = 0.003).

These data suggest that children exposed to either F or As have increased risks of reduced IQ scores.


“The health effects in humans associated with exposure to F (skeletal and dental fluorosis and reproductive effects) or As (skin, bladder, and lung cancer) are well documented.Also, the literature reports neurological consequences associated with exposure to F or As. In children, the most reported effect is on cognitive capacities, particularly intelligence reduction.”

“The evidence of F and As neurotoxicity is supported by animal studies, which show cognitive deficits are associated with F exposure, and behavioral changes (locomotor activity) and delayed learning are associated with As exposure.”

“So far, the studies have evaluated only the individual effect of F or As on IQ, without taking into account that they may share the same source of exposure (drinking water, coal etc.). Accordingly, considering that both contaminants have been shown to be neurotoxicants, the objective of this study was to explore the influence of both F and As on IQ in children living in three rural areas with contrasting levels of F and As.

Variables adjusted for in this study: Age, nutritional status (height and weight by age, iron status), socioeconomic status (including mother’s education), blood lead (Pb).

Fluoride and arsenic exposure quantification: Drinking water was collected on day of biological evaluation, F content was measured using TISAB and specific ion electrode, and As content using spectrophotometry. Urine F and As were also quantified using established methods.


“We found that exposure to F in urine was associated with reduced Performance, Verbal, and Full IQ scores before and after adjusting for confounders (β values = -13.0, -15.6, and -16.9, respectively; all p-values < 0.001). The same pattern was observed for models with F in water as the exposure variable (β values = -6.7, -11.2, and -10.2, respectively; all p-values < 0.001).

“The individual effect of F in urine indicated that for each mg increase of F in urine a decrease of 1.7 points in Full IQ might be expected. The proportion attributable to F in urine alone was 17% above the contribution of other measured factors.”

“We also observed an inverse relationship for Performance and Verbal IQ scores, although with less significance (β = -4.19, p = 0.08; β = -5.50, p = 0.06, respectively). We also found that As in water was inversely correlated with Performance, Verbal, and Full IQ scores (β values = -4.30, -6.40, and -6.15; all p values < 0.001).”

“Compared to F, the effect attributable to As was smaller.”

Neurotoxicity of fluoride and arsenic reaffirmed 

“The adverse effects of F and As on the human central nervous system are supported by experimental data. When F crosses the blood brain barrier, the hematoencephalic barrier, it accumulates in the brain, inducing structural and cognitive alterations in the central nervous system. Rats exposed to F in drinking water at weaning had elevated fluoride levels in 6 of 7 brain regions and plasma fluoride levels 7 to 42 times higher than those found in control animals. These elevated plasma and brain F levels were associated with behavior alterations, such as cognitive deficits. Learning deficits in a delayed alternation task and alterations in a spatial learning task have been reported for groups exposed to As as compared to control groups.”

“The design of the present study precluded testing statistically the interaction between F and As. However, a previous study conducted by our research group in the city of San Luis Potosí, IQ scores were evaluated using WISC-RM in a population of children exposed to F in drinking water (values ranged from 1.5 to 3mg/L). The mean levels of F and As in urine were 4.3±1.5mg/g crt and 41±1.5μg/g crt, respectively. This study did not demonstrate any effect on IQ scores, but did show a positive relationship between F in urine and reaction time (r = 0.28, p = 0.04) and an inverse inverse relationship between F in urine and visualspatial organization scores (r = -0.27, p = 0.05).

“These data may lend support to the hypothesis that exposure to both toxicants could worsen children’s performance on neuropsychological tests and thus indicates the need for further investigation.”

“Some of the effects on brain dysfunctions are observed years after exposure.”


“In conclusion, the data from this research support the conclusion that F and As in drinking water have a potential neurotoxic effect in children. It is urgent that public health measures to reduce exposure levels be implemented. Millions of people around the world are exposed to these pollutants and are therefore potentially at risk for negative impact on intelligence. This risk may be increased where other factors affecting central nervous system development, such as malnutrition and poverty, are also present. The risk is particularly acute for children, whose brains are particularly sensitive to environmental toxins.

“Furthermore, it would be advisable to reexamine the benefits of F given the documented health risks.”