The composition of drinking water and the prevalence of anencephalus and spina bifida in New Zealand.

A study was conducted in a cohort of New Zealand births on the prevalence of anencephalus and spina bifida in relation to various chemical elements in the drinking water. Cases were ascertained from national infant mortality and late fetal death records, and public hospital records and consisted of still and live births (of 28 or more weeks gestation) during 1978-1982 with anencephalus or spina bifida diagnosed either at birth or during the first year of life. The 460 cases were matched with their official birth registration records and a sample of 5000 control births was randomly selected from all non-NTD still- and livebirths. Drinking water data were obtained from a national surveillance program. Iron was the only water element to be included in the stepwise multiple logistic regression model of anencephalus prevalence, and magnesium, sulphate, and nitrate nitrogen were retained in the spina bifida model. This indicates a statistically significant association between these elements and the respective outcome. The results for iron and nitrate nitrogen were contrary to findings from previous studies. Despite the methodological problems associated with such ecological studies, there are indications that the constituents of a water supply may have an impact on the risk of NTDs.