Study shows adverse effects from > 800 ug/d daily iodine intake

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Here's a study about the safe upper limit of iodine that will get you all riled

up.

http://www.ajcn.org/content/early/2011/12/26/ajcn.111.028001.abstract

Exploration of the safe upper level of iodine intake in euthyroid Chinese

adults: a randomized double-blind trial1,2,3

Abstract

Background: The beneficial health effects associated with Universal Salt

Iodization are well known. Yet, little is known about the possible adverse

health effects in people with high iodine intake and the safe daily intake upper

limit in the Chinese population.

Objective: The objective of this study was to explore the safe upper level of

total daily iodine intake among adults in China.

Design: A 4-wk, double-blind, placebo-controlled, randomized controlled trial

was conducted in 256 euthyroid adults. Participants were randomly assigned to 12

intervention groups with various iodine supplement doses ranging from 0 to 2000

& #956;g/d. Total iodine intake included iodine from both supplements and diet.

Multiple outcome measures were used to evaluate possible adverse effects,

including thyroid function, thyroid size, and urinary iodine.

Results: The mean iodine intake from the diets and salt intake of the

participants were 105 ± 25 and 258 ± 101 & #956;g/d, respectively. In comparison

with the placebo group, all iodide-supplemented groups responded with

significant increases in median urinary iodine concentrations (P < 0.05) and in

thyroid-stimulating hormone concentration (P < 0.05). Thyroid volume decreased

after 4 wk in the high-iodine intervention groups (1500–2000 & #956;g).

Subclinical hypothyroidism appeared in the groups that received 400 & #956;g I

(5%) and 500–2000 & #956;g I (15–47%).

Conclusions: This study showed that subclinical hypothyroidism appeared in the

participants who took the 400- & #956;g I supplement, which provided a total

iodine intake of & #8764;800 & #956;g/d. Thus, we caution against a total daily

iodine intake that exceeds 800 & #956;g/d in China and recommend further research

to determine a safe daily upper limit.

Received January 3, 2011.

Accepted November 16, 2011.