Recently I suggested that Attention Deficit Hyperactivity Disorder (ADHD) was better correlated with elevation than with community water fluoridation (see ADHD linked to elevation not fluoridation). I criticised the study of Malin and Till (2015) for limiting their investigation to a chemical toxicity hypothesis and pointed out that once confounding factors like elevation are included their reported relationship between ADHD and community water fluoridation (CWF) disappears.
Seems I am not the only one to notice this. A new paper reports that same relationship:
Huber, R. S., Kim, T.-S., Kim, N., Kuykendall, M. D., Sherwood, S. N., Renshaw, P. F., & Kondo, D. G. (2015). Association Between Altitude and Regional Variation of ADHD in Youth. Journal of Attention Disorders.
They used data sets for the prevalence of ADHD in 2007 and 2010 in US states and found a negative relationship with average state elevation. Their correlation coefficients (R 2 = .38, p < .001; R 2 = .31, p < .001 respectively) are similar to the one I found.
This paper effectively supports my earlier conclusion:
“I do not think Malin and Till (2015) are justified in drawing the conclusion that CWF influences ADHD. Their mistaken conclusion has arisen from their limited choice of data considered for the exploratory analysis. That in itself seems to have resulted from a bias inherent in their hypothesis that “fluoride is a widespread neurotoxin.”
I was not advancing an alternative hypothesis but Huber et al., (2015) did suggest the hypothesis:
“As decreased dopamine (DA) activity has been reported with ADHD and hypoxia has shown to be associated with increased DA, we hypothesized that states at higher altitudes would have lower rates of ADHD.”
But the important lesson is once factors like elevation are taken into account there is no statistically significant relationship with CWF. The Malin & Till (2015) paper currently heavily promoted by anti-fluoride propagandists is flawed.