The prevalence of iodine deficiency in women of reproductive age in the United States of America.

OBJECTIVE: To review the iodine status of women as assessed through National Health and Nutrition Examination Surveys from 1971 to 2002.

DESIGN AND SETTING: National normative estimates of iodine status of the civilian, non-institutionalized population in the United States of America.

SUBJECTS: Women of reproductive age and pregnant women.

RESULTS: In the United States of America, iodine began to be added to the diet in the 1920s. An excessive iodine intake was documented by the first National Health and Nutrition Examination Survey (NHANES I) in the 1970s which reported a median urinary iodine (UI) concentration of 320 microg l-1. In the NHANES III survey, conducted between 1988 and 1994, the median UI concentration had decreased to 145 microg l-1, while 14.9% of women aged 15-44 years and 6.9% of pregnant women had a UI concentration 50 microg l-1. The concentrations of serum T4 and thyroid-stimulating hormone of women with a low UI concentration did not, however, indicate an iodine deficiency.

CONCLUSIONS: Further studies of the association between iodine excretion and biochemical and physiological changes should be undertaken to better understand women's needs for iodine and to develop criteria to monitor them in pregnancy. Because of the potential harm caused by iodine deficiency during pregnancy, we support the use of iodine supplements for all pregnancies while these data are being collected.