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Table 2 Before-and-after studies on the effect of salt iodization on type of thyroid cancer. The effect of introduction of salt iodization or an increase in the salt iodization level on the sex ratio (female: male, F:M) of affected subjects and the subtypes of thyroid cancer, by country: changes in the papillary thyroid cancer to follicular thyroid cancer ratio (PTC:FTC), and the percentage of anaplastic thyroid cancer (% ATC).

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

Country (reference) Years pre-iodized salt Year and change in salt iodization Years post-iodized salt
PTC:FTC % ATC F:M PTC:FTC % ATC F:M
Basel, Switzerland [148] 1944–1953 1962 1964–1973
0.27 28.7 2.5 Increase from 5 to 10 ppm 0.74 27.7 2.5
Zurich, Switzerland [67] 1925–1941 1962 1962–1973
0.19 36.9 1.3 Increase from 5 to 10 ppm 1.1 23.8 2.1
Innsbruck, Austria [66] 1952–1959 1963 1970–1975
0.21 na 0.9 Introduction at 10 ppm 1.1 na 1.9
Tyrol, Austria [98] 1952–1975 1963; 1992 1986–1995
0.55 28.4 na Introduction at 10 ppm; increase to 20 ppm 1.5 4.9 na
Klagenfurt, Austria [149] 1984–1989 1992 1990–1995
2.6 na na Increase from 10 to 20 ppm 4.0 na na
Krakow and Nowy Sacz, Poland [150] 1986 1997 2001
1.0 na na Introduction at 30 ppm 5.9 na na
Lower Franconia, Germany [99] 1981–1985 1993 1991–1995
1.5 11.3 3.0 Increased use by the food industry at 20 ppm 3.4 7.3 2.2
Salta, Argentina [95] 1958–1972 1963; 1970 1985–2007
1.7 16.9 2.9 Introduction at 40 ppm; decrease to 33 ppm 3.9 6.4 4.0
Galicia, Spain [84] 1978–1985 1985 1994–2001
2.3 na 4.3 Introduction at 60 ppm 11.5 na 3.4
Parma, Italy [100] 1998–2003 2005 2004–2009
13.0 2.3 3.1 Introduction at 30 ppm 13.6 1.0 3.2
Shenyang, China [86] 1992–1996 1995; 2000 1997–2009
2.3 7.1 3.2 Introduction at 20–60 ppm; decrease to 35 ppm 21.9 2.1 3.6