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

Background: In 1993 the compulsory iodization of salt was introduced in Zim babwe. a country that was previously an area of severe iodine deficiency. Objective: The objective of this study was to document urinary iodine excre tion and biochemical thyroid function in seemingly healthy, community-dwell ing,adults after the introduction of iodization. Design: A multistage, random sampling method was used in I rural and urban settings to identify households from which the senior household member (age d >35 y) was recruited (alternating male and female recruits). Demographic data were collected for each subject and urinary and venous blood samples w ere taken. Urinary iodine excretion and serum thyroid hormone status (thyro tropin and total thyroxin) were evaluated according to age, sex, and area o f residence. Results: A total of 736 adults were recruited (253 men: mean age: 64 y). Ur inary iodine concentrations were high [median (first and third quartiles): 4.41 (2.84, 6.78) mu mol/L, or 560 (360, 860) mu g/L] and were significantl y higher in rural areas than in urban areas [4.73 (3.07, 7.14) mu mol/L, or 600 (390. 906) mu g/L, compared with 3.47 (2.05, 4.73) mu mol/L, or 440 (2 60, 600) mu g/L; P < 0.001]. Urinary iodine excretion declined significantl y with increasing age (r = -0.29, P < 0.001). Serum thyroid status suggeste d that the prevalence of biochemical hyperthyroidism in the study was 3%. w ith 13 of 415 cases in rural and 3 of 149 cases in urban subjects. Conclusion: This study reaffirms the need to continuously monitor iodine re placement programs to ensure efficacy.