Grimes and Newton et al have made a number of criticisms of our paper, including that we misrepresent conclusions of the existing literature; do not adequately take account of confounding factors; have used arbitrary cut-offs in categorising the variables; and made an error in reporting the results of the model.1 ,2 We welcome the opportunity to respond to these criticisms and, in particular, address the claim made by Newton et al that we made an error in reporting the results of our model. We acknowledge the substantial problem of poor oral health that affects some children and adults in the UK and do not question that there is substantial good quality evidence to support the topical use of fluorides in toothpaste, nor do we wish to see the removal of effective and safe oral health programmes. The paper is not a discussion of the benefits or otherwise of water fluoridation programmes as these are discussed elsewhere.3–5 The focus of our paper was on whether fluoride levels in drinking water were associated with the prevalence of hypothyroidism.

The Journal's restriction on paper length and number of references meant that we were not able to fully discuss the literature on fluoride and the thyroid. Consequently, we referred to the discussion from the NRC report, believing that to provide a sufficient basis to consider a plausible relationship.6 We accept that the primary causes of hypothyroidism are varied, including autoimmune disease and surgical intervention. Grimes1 states that the NRC …