Needleman HL, Pueschel SM, Rothman KJ. Fluoridation and the occurrence of down's syndrome. N Engl J Med. 1974 Oct 17;291(16):821-3. doi: 10.1056/NEJM197410172911604

The prevalence rates of Down's syndrome at birth were compared for Massachusetts residents ingesting fluoridated and non-fluoridated water. The observations included nearly all children born alive with Down's syndrome in Massachusetts during the 17-year period 1950–1966. A rate of 1.5 cases per 1000 births was found both for fluoride-related births and appropriate comparison groups; the upper bound of a one-sided 95 per cent confidence interval for the ratio of fluoride to non-fluoride rates was 1.2. Thus, the data provide strong evidence that fluoridation does not cause any important elevation in risk for Down's syndrome, at least not for several years after its introduction

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