New questions and insights into nitrate/nitrite and human health effects: a retrospective cohort study of private well users' immunological and wellness status.

The retrospective cohort study described in this article examined 150 Iowa private well users' (aged 1-60 years) drinking water below the 10 parts per million nitrate-nitrogen (nitrate-N) maximum contaminant level and analyzed health history data and blood samples including hemoglobin fractions and immunological parameters. Positive associations existed (bivariate fit) between higher nitrate exposure and body mass index, lower recreational activity, perceived poorer health, and perceptions of susceptibility to illness. A directly proportionate relationship was seen between methemoglobin level in the blood and nitrate ingestion. High tumor necrosis factor-beta (TNF-beta) expression was also seen (bivariate fit, f = 3.76, p = .05). Complaints of stomach/ intestinal difficulties (heartburn/reflux > 50%; f = 5.274, p = .0231) and bone, muscle, and nerve complaints (osteoarthritis [rheumatoid excluded] = 47%; f = 6.0533, p = .0150) were found with increasing nitrate exposure. In vivo exposures of nitrate-N associated with complaints of bone/joint disorders or with altered ex vivo production of TNF-beta or Th2/Treg cytokine interleukin-10 have not been previously illustrated with environmental exposures.