CONTEXT: Iodine fortification (IF) of salt was introduced in Denmark in 1998. Little is known about the effect of a minor increase in iodine intake on the incidence of hypothyroidism. We prospectively identified all new cases of overt hypothyroidism in two areas of Denmark before and for the first 7 yr after IF had been introduced. METHODS: A computer-based register was used to identify continuously all new cases of overt hypothyroidism in two subcohorts with previous moderate and mild iodine deficiency (ID), respectively (Aalborg, n = 310,124, urinary iodine = 45 microg/liter; and Copenhagen, n = 225,707, urinary iodine = 61 microg/liter). Data were obtained 1) before IF (1997-1998), 2) during voluntary IF (1999-2000), 3) during early (2001-2002) and 4) during late (2003-2005) period with mandatory IF. RESULTS: The overall incidence rate of hypothyroidism increased during the study period: baseline, 38.3/100,000.yr; voluntary IF, 43.7 (not significant vs. baseline); early mandatory IF, 48.7 [vs. baseline, rate ratio (RR) = 1.27; 95% confidence interval (CI) = 1.10-1.47]; and late mandatory IF, 47.2 (vs. baseline, RR = 1.23; 95% CI = 1.07-1.42). There was a geographic difference because hypothyroidism increased only in the area with previous moderate ID: Aalborg, late mandatory IF vs. baseline, 40.3/29.7 (RR = 1.11; 95% CI = 1.11-1.66); Copenhagen, 56.7/51.6 (RR = 1.10; 95% CI = 0.90-1.34). The increase occurred in young and middle-aged adults. CONCLUSION: Even a cautious iodization of salt was accompanied by a moderate increase in the incidence rate of overt hypothyroidism. This occurred primarily in young and middle-aged subjects with previous moderate ID.
CONTEXT: Iodine fortification (IF) of salt was introduced in Denmark in 1998. Little is known about the effect of a minor increase in iodine intake on the incidence of hypothyroidism. We prospectively identified all new cases of overt hypothyroidism in two areas of Denmark before and for the first 7 yr after IF had been introduced. METHODS: A computer-based register was used to identify continuously all new cases of overt hypothyroidism in two subcohorts with previous moderate and mild iodine deficiency (ID), respectively (Aalborg, n = 310,124, urinary iodine = 45 microg/liter; and Copenhagen, n = 225,707, urinary iodine = 61 microg/liter). Data were obtained 1) before IF (1997-1998), 2) during voluntary IF (1999-2000), 3) during early (2001-2002) and 4) during late (2003-2005) period with mandatory IF. RESULTS: The overall incidence rate of hypothyroidism increased during the study period: baseline, 38.3/100,000.yr; voluntary IF, 43.7 (not significant vs. baseline); early mandatory IF, 48.7 [vs. baseline, rate ratio (RR) = 1.27; 95% confidence interval (CI) = 1.10-1.47]; and late mandatory IF, 47.2 (vs. baseline, RR = 1.23; 95% CI = 1.07-1.42). There was a geographic difference because hypothyroidism increased only in the area with previous moderate ID: Aalborg, late mandatory IF vs. baseline, 40.3/29.7 (RR = 1.11; 95% CI = 1.11-1.66); Copenhagen, 56.7/51.6 (RR = 1.10; 95% CI = 0.90-1.34). The increase occurred in young and middle-aged adults. CONCLUSION: Even a cautious iodization of salt was accompanied by a moderate increase in the incidence rate of overt hypothyroidism. This occurred primarily in young and middle-aged subjects with previous moderate ID.
Authors: Charlotte Cerqueira; Nils Knudsen; Lars Ovesen; Peter Laurberg; Hans Perrild; Lone Banke Rasmussen; Torben Jørgensen Journal: Eur J Epidemiol Date: 2011-06-10 Impact factor: 8.082
Authors: Peter N Taylor; Diana Albrecht; Anna Scholz; Gala Gutierrez-Buey; John H Lazarus; Colin M Dayan; Onyebuchi E Okosieme Journal: Nat Rev Endocrinol Date: 2018-03-23 Impact factor: 43.330
Authors: Rainbow Rubin; Michelle Pearl; Martin Kharrazi; Benjamin C Blount; Mark D Miller; Elizabeth N Pearce; Liza Valentin-Blasini; Gerald DeLorenze; Jane Liaw; Andrew N Hoofnagle; Craig Steinmaus Journal: Environ Res Date: 2017-06-09 Impact factor: 6.498
Authors: Simone A Johner; Michael Thamm; Peter Stehle; Ute Nöthlings; Eugen Kriener; Henry Völzke; Roland Gärtner; Thomas Remer Journal: Thyroid Date: 2014-06-05 Impact factor: 6.568