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Howard Backer¹ and Joe Hollowell²

¹University of California San Francisco and Berkeley, Kaiser Permanente Northern California, Oakland, California, USA
²National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

Iodine is an effective, simple, and cost-efficient means of water disinfection for people who vacation, travel, or work in areas where municipal water treatment is not reliable. However, there is considerable controversy about the maximum safe iodine dose and duration of use when iodine is ingested in excess of the recommended daily dietary amount. The major health effect of concern with excess iodine ingestion is thyroid disorders, primarily hypothyroidism with or without iodine-induced goiter. A review of the human trials on the safety of iodine ingestion indicates that neither the maximum recommended dietary dose (2 mg/day) nor the maximum recommended duration of use (3 weeks) has a firm basis. Rather than a clear threshold response level or a linear and temporal dose-response relationship between iodine intake and thyroid function, there appears to be marked individual sensitivity, often resulting from unmasking of underlying thyroid disease. The use of iodine for water disinfection requires a risk-benefit decision based on iodine's benefit as a disinfectant and the changes it induces in thyroid physiology. By using appropriate disinfection techniques and monitoring thyroid function, most people can use iodine for water treatment over a prolonged period of time. Key words: goiter, iodine, thyroid disorders, thyroid hormones, water purification, water supply. Environ Health Perspect 108:679-684 (2000) . [Online 21 June 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p679-684backer/ abstract.html

Address correspondence to H. Backer, 109 Bonita Ave., Piedmont, CA 94611 USA. Telephone: (510) 601-5134. Fax: (510) 601-5134. E-mail: hdbacker@aol.com

We thank J.A.T. Pennington, J.T. Dunn, P.O. Bohan, and D.T. Miller for editorial review. L. Kettel-Kahn and L. Muszymski-Compton helped with the literature search and provided editorial assistance.

Received 1 February 2000 ; accepted 24 March 2000.