Urinary iodine concentrations and thyroid function in adult Zimbabweans during a period of transition in iodine...

In 1993 the compulsory iodization of salt was introduced in Zimbabwe, a country that was previously an area of severe iodine deficiency.

The objective of this study was to document urinary iodine excretion and biochemical thyroid function in seemingly healthy, community-dwelling adults after the introduction of iodization.

A multistage, random sampling method was used in rural and urban settings to identify households from which the senior household member (aged >35 y) was recruited (alternating male and female recruits). Demographic data were collected for each subject and urinary and venous blood samples were taken. Urinary iodine excretion and serum thyroid hormone status (thyrotropin and total thyroxin) were evaluated according to age, sex, and area of residence.

A total of 736 adults were recruited (253 men; mean age: 64 y). Urinary iodine concentrations were high [median (first and third quartiles): 4.41 (2.84, 6.78) micromol/L, or 560 (360, 860) microgram/L] and were significantly higher in rural areas than in urban areas [4.73 (3.07, 7.14) micromol/L, or 600 (390, 906) microgram/L, compared with 3.47 (2.05, 4.73) micromol/L, or 440 (260, 600) microgram/L; P < 0.001]. Urinary iodine excretion declined significantly with increasing age (r = -0.29, P < 0.001). Serum thyroid status suggested that the prevalence of biochemical hyperthyroidism in the study was 3%, with 13 of 415 cases in rural and 3 of 149 cases in urban subjects.

This study reaffirms the need to continuously monitor iodine replacement programs to ensure efficacy.