Authors' reply.

Sir,

Thank you very much for providing us an opportunity to respond to comments in the ‘Letter to Editor’[1] for the manuscript titled “Effect of fluoride exposure on the intelligence of school children in Madhya Pradesh, India”.[2] Our clarification for the issues raised in the ‘Letter to Editor’[1] is as follows: (1) There are studies which show that education level of parents, socioeconomic status of the family, nutrition, iodine deficiency, lead, arsenic affect the intellectual ability of children. But in our study, we could not find significant difference between four groups (based on water fluoride level) for these variables. And this is clearly mentioned in the result section (Table 1 and 2) and discussion section.[2] As per the suggestion by our biostatician, non-significant factors were not included in regression analysis. Although for our interest, we did regression analysis using all the independent variables mentioned in (Tables 1 and 2), results were same as mentioned in result section.[2] We think, it is very simple to understand that non-significant factors will not show any significant relationship with dependent variable in regression analysis. (2) We do agree, our study does not establish cutoff point of the water fluoride level at which deterioration of intelligence begins. There is a need for further research and debate for the same. We had chosen the value of < 1.5 PPM for low fluoride group based on the recommended level of fluoride in drinking water by WHO[3] and Bureau of Indian Standards (maximum permissible limit).[4]