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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