In a meta-analysis of 27 mostly China-based studies on fluoride and neurotoxicity, researchers from Harvard School of Public Health and China Medical University in Shenyang found strong indications that fluoride may adversely affect cognitive development in children [50]. All but one study suggested that high fluoride content in water may negatively affect cognitive development. The average loss in intelligence quotient (IQ) was reported as a standardized weighted mean difference of 0.45, which would be approximately equivalent to seven IQ points for commonly used IQ scores with a standard deviation of 15 [50]. While fluoride's effect on IQ in this meta-analysis did not reach statistical significance, the combined effect at population level is remarkable. A particular concern of the NRC committee was the impact of ingested fluoride on the thyroid gland [49]. In a 2005 study, it was found that 47% of children living in a New Delhi neighbourhood with average water fluoride level of 4.37 ppm have evidence of clinical hypothyroidism attributable to fluoride. They found borderline low FT3 levels among all children exposed to fluoridated water [51]. The mechanisms through which fluoride exacerbates hypothyroidism include competitive binding with iodine, as well as synthesis obstruction of T3 and T4. These mechanisms explain the use of fluoride at doses above 5 mg/day in the treatment of hyperthyroidism [52, page 451]. Thus, fluoride-induced hypothyroidism is likely to be more common in iodine-deficient settings. Australian surveys indicate that the general Australian population is mildly deficient in iodine [53] Iodine-deficient children ingesting fluoridated water have been found to demonstrate intellectual deficits even at water fluoride levels of 0.9 ppm [54].