Urinary iodine and thyroid status of New Zealand residents

Abstract

Objectives: The aim of this project was to assess the clinical signi®cance of our low iodine excretions in terms of thyroid hormone status and thyroid volume in an adult population in a low soil iodine area of the South Island of New Zealand. Design and setting: Two-hundred and thirty-three residents of Otago, New Zealand collected two 24 h urine samples for assessment of iodine status. Thyroid status was determined from serum total T 4 , TSH and thyroglobulin, and thyroid volumes. Relationships between urinary iodide excretion and measures of thyroid status were determined and subjects were allocated to one of three groups according to low, medium and high iodide excretion, for comparison of thyroid hormones and thyroid volumes. Results: Signi®cant correlations were found for relationships between measures of urinary iodide excretion and thyroid volume and thyroglobulin. Multiple regression analysis of data for subjects divided into three groups according to 24 h urinary iodide excretion (`60, 60 ± 90; b90 mg iodideaday) or iodideacreatinine ratio (`40; 40 ± 60; b60 mgag Cr) showed signi®cant differences in thyroid volume (P 0.029; P 0.035, respectively) and thyroglobulin (P 0.019; P 0.005, respectively) among the groups. Conclusions: The results of this study con®rm the low iodide excretions of Otago residents, and indicate that the fall in iodine status is being re¯ected in clinical measures of thyroid status, including enlarged thyroid glands and elevated thyroglobulin. Our observations suggest the possible re-emergence of mild iodine de®ciency and goitres in New Zealand. This situation is likely to worsen should iodine intakes continue to fall and continued monitoring of the situation is imperative.

Minimal impact of excess iodate intake on thyroid hormones and selenium status in older New Zealanders

“…Selenium supplementation increased GPx activity, confirming many other intervention studies carried out in New Zealand, which indicate that the baseline selenium status of New Zealanders is insufficient for maximization of GPx activity (12). However, we observed a statistically significant smaller increase in GPx in the SeChighI group than in the other selenium-supplemented groups.…”

“…Many of our older participants would have been born in the 1930s when iodine deficiency goiter was prevalent in many parts of New Zealand until adequate iodization of salt was introduced in the early 1940s. From that time until the 1980s was a time of adequate iodine status throughout the country because of high iodine content of dairy products as a result of the use of iodophor cleaning agents in the dairy industry, as well as iodized salt use (12). In the past 10-15 years, the use of iodophors has reduced resulting in a decrease in iodine status and a return to mild iodine deficiency from the early 1990s (11)(12)(13).…”

“…From that time until the 1980s was a time of adequate iodine status throughout the country because of high iodine content of dairy products as a result of the use of iodophor cleaning agents in the dairy industry, as well as iodized salt use (12). In the past 10-15 years, the use of iodophors has reduced resulting in a decrease in iodine status and a return to mild iodine deficiency from the early 1990s (11)(12)(13). Thus, our participants may have had varied historical exposure to iodine deficiency depending on their place of residence in New Zealand during their lifetime.…”

“…Iodine status in New Zealand has decreased over the past two decades because of reduction in use of iodophor cleaning agents in the dairy industry and iodized table salt, resulting in re-emergence of mild iodine deficiency (11)(12)(13). The elderly are particularly vulnerable because they consume fewer servings of dairy products (14).…”

Selenium and iodine supplementation: effect on thyroid function of older New Zealanders

“…New Zealanders have experienced a return to mild-moderate iodine deficiency, with elevated serum thyroglobulin and enlarged thyroid glands (6)(7)(8). Although selenium status has increased, intakes for many New Zealanders are still insufficient for maximal GPx activity (8)(9)(10).…”