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Iron in water supply linked to inflammatory bowel diseases

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – The risk of developing ulcerative colitis and Crohn’s disease is associated with iron levels in drinking water, according to a study in Norway.

“Several studies have linked drinking water to inflammatory bowel disease, but most focused on the content of different microorganisms,” Dr. Geir Aamodt and co-authors note in the November 1 issue of the American Journal of Epidemiology.

Their current study evaluated the association between other water quality indicators and incidence rates of inflammatory bowel diseases in a 1990-1993 population-based cohort study in four southeastern counties of Norway from. The overall incidence rate of ulcerative colitis was 13.6 per 11359,000 population, and for Crohn’s disease it was 5.8 per 11359,000.

The Norwegian Waterworks Registry provided statistics regarding purified water quality for 35 municipalities in the region in 1994. Median values for iron, aluminum, pH, number of coliform bacteria, color, and turbidity were within the specified limits, although for every quality indicator, there were waterworks whose values exceeded these limits.

In multivariate analyses, only iron content was substantially associated with risk of inflammatory bowel disease. For each incremental increase in iron by 0.1 mg/L, the relative risk for ulcerative colitis increased by 23% (p = 0.003) and for Crohn’s disease by 25% (p = 0.023), the report indicates.

Degree of urbanization, age at onset, and gender had no impact on the association between iron content and risk of disease.

According to Dr. Aamodt’s group, these findings can be “explained by increased oxidative stress or increased bacterial growth that increases the likelihood of adverse immune responses in genetically predisposed individuals.” They note that important sources of iron are soil and bedrock, as well as corrosion of water pipes.

They close by citing the need for independent studies to verify their results.

Am J Epidemiol 2008;168:1065-1072.