Iodine intake as a risk factor for thyroid cancer: a comprehensive review of animal and human studies

Table 3 Prevalence of occult thyroid cancer in adults at autopsy, by national iodine status. National population iodine status at the time of study as categorized according to WHO criteria for the median urinary iodine concentration (UIC) [23].^a

Country (reference)	Year	No. autopsy cases	% with occult thyroid cancer
Probable deficient iodine intake (UIC < 100 μg/L) (n = 11)
Italy [151]	1982	111	3.6
Chile [152]	1984	274	2.9
Poland [108]	1975	110	6.6
Portugal [153]	1979	600	1.0
Israel [154]	1981	260	4.2
Germany [155]	1987	1020	6.1
Spain [156]	1993	100	22.0
Belarus [157]	1993	215	8.8
Ukraine [158]	1996	162	10.8
Guatemala [159]	2005	150	2.0
Hungary [109]	2005	222	5.0
Mean			6.6
Weighted mean			5.3
Probable sufficient iodine intake (UIC = 100–299 μg/L) (n = 10)
Canada [108]	1975	100	6.0
Sweden [160]	1981	500	6.4
USA [161]	1988	138	2.9
Brazil [162]	1989	300	1.0
Argentina [163]	1989	100	11.0
Iceland [164]	1992	199	6.0
Singapore [165]	1994	444	9.0
Austria [110]	2001	118	8.6
Greece [166]	2002	160	5.6
Turkey [167]	2011	108	3.7
Mean			6.0
Weighted mean			6.0
Probable excessive iodine intake (UIC ≥ 300 μg/L) (n = 10)
USA [168]	1952	429	0.9
USA [169]	1955	1000	2.8
USA [170]	1955	221	1.4
USA [171]	1964	100	4.0
USA [172]	1966	300	2.7
USA [173]	1969	220	0.5
USA [174]	1974	157	5.7
Columbia [108]	1975	607	5.6
Hungary [109]	2005	221	4.5
Brazil [175]	2006	166	7.8
Mean			3.6
Weighted mean			3.3
Studies of Japanese populations in areas of excessive iodine intake (n = 5)
USA, Japanese [176]	1971	100	24.0
Japan [174]	1974	1096	17.9
USA, Japanese [108]	1975	248	^24.2
Japan [108]	1975	1167	28.4
Japan [111]	1990	408	15.7
Mean			22.0
Weighted mean			22.4

^aWeighted means of iodine intake categories compared by using the Chi-squared test of independence: <100 μg/L vs. 100–299 μg/L (p = 0.244); ≥300 μg/L vs. <100 μg/L or 100–299 μg/L (both, p < 0.001)

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