Mandatory iodine fortification of bread and salt increases iodine excretion in adults in Denmark – A 11-year follow-up study

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Objective: Our objective was to investigate individual serum thyroglobulin (Tg) changes in relation to iodine fortification (IF) and to clarify possible predictors of these changes. Design: We performed a longitudinal population-based study (DanThyr) in two regions with different iodine intake at baseline: Aalborg (moderate iodine deficiency (ID)) and Copenhagen (mild ID). Participants were examined at baseline (1997) before the mandatory IF of salt (2000) and again at follow-up (2008) after IF. Methods: We examined 2465 adults and a total of 1417 participants with no previous thyroid disease and without Tg-autoantibodies were included in the analyses. Serum Tg was measured by immunoradiometric method. We registered participants with a daily intake of iodine from supplements in addition to IF. Results: Overall, the follow-up period saw no change in median Tg in Copenhagen (9.1/9.1 mg/l, PZ0.67) while Tg decreased significantly in Aalborg (11.4/9.0 mg/l, P!0.001). Regional differences were evident before IF (Copenhagen/Aalborg, 9.1/11.4 mg/l, P!0.001), whereas no differences existed after IF (9.1/9.0 mg/l, PZ1.00). Living in Aalborg (P!0.001) and not using iodine supplements at baseline (PZ0.001) predicted a decrease in Tg whereas baseline thyroid enlargement (PZ0.02) and multinodularity (PZ0.01) were associated with an individual increase in Tg during follow-up. Conclusions: After IF we observed a decrease in median Tg in Aalborg and the previously observed regional differences between Aalborg and Copenhagen had levelled out. Likewise, living in Aalborg was a strong predictor of an individual decrease in serum Tg. Thus, even small differences in iodine intake at baseline were very important for the individual response to IF.

Section: European Journal Of Endocrinologysupporting

confidence: 78%

Section: Previous Studiesmentioning

confidence: 90%

Section: European Journal Of Endocrinologymentioning

confidence: 99%

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Serum thyroglobulin before and after iodization of salt: an 11-year DanThyr follow-up study

Krejbjerg

Bjergved

Pedersen

et al. 2015

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“…While a limitation of the present study is the lack of data on urinary iodine levels, studies from the background population in the same area have shown significantly improved urinary iodine levels albeit in the low range of recommended levels (25). However, the iodine status of young women may not be sufficient to meet the increased demands during pregnancy.…”

Section: Thyroid Function After the Iodine Fortification Programmentioning

confidence: 66%

Thyroid function and autoimmunity in Danish pregnant women after an iodine fortification program and associations with obstetric outcomes

Bliddal

Boas

Hilsted

et al. 2015

Objective: Aberrations in maternal thyroid function and autoimmunity during pregnancy have been associated with negative obstetric outcome. In Denmark, a national iodine fortification program was implemented in the year 2000 with the aim to alleviate the mild-moderate iodine deficiency. Following the iodine implementation, there has been an increase in thyroid autoimmunity in the background population. This study investigates the thyroid status of pregnant Danish women following the iodine fortification program, and a possible association with preterm delivery. Design: Historical cohort study of 1278 randomly selected pregnant Danish women attending the national Down's syndrome screening program. Methods: The main outcome measures were thyroid status according to laboratory-and gestational-age-specific reference intervals, and association with risk of abnormal obstetric outcome. Antibody-positivity was defined as an antibody-level (thyroid peroxidase and/or thyroglobulin antibodies) above 60 U/ml. Results: Establishing laboratory-specific gestational-age-dependent reference intervals, we found a prevalence of maternal thyroid dysfunction of 10%-15.8% by use of the cut-off suggested by the American Thyroid Association. Thyroid dysfunction was significantly associated with antibody-positivity (P!0.05). No associations were found between preterm delivery and thyroid dysfunction (adjusted OR 0.6, 95% CI: 0.1-2.3) or autoimmunity (adjusted OR 1.1, 95% CI: 0.4-2.7). Conclusions: After the implementation of the Danish iodine fortification program, the prevalence of thyroid dysfunction and autoimmunity in Danish pregnant women is high -even higher by use of pre-established reference intervals from international consensus guidelines. However, no associations were found with abnormal obstetric outcome. Large randomized controlled trials are needed to clarify the benefit of treating slight aberrations in pregnant women's thyroid function.

“…When a urine sample containing 93.9 mg/l was measured in triplicate in 18 assays, the intra-assay coefficient of variation (CV) for single determinations was 2.1% and the inter-assay CV was 2.7% (19). The iodine laboratory was certified by the U.S. Centers for Disease Control and Prevention's EQUIP Program.…”

Section: Laboratory Proceduresmentioning

confidence: 99%

Iodine fortification may influence the age-related change in thyroid volume: a longitudinal population-based study (DanThyr)

Krejbjerg

Bjergved

Pedersen

et al. 2014

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Objective: To assess the individuals' thyroid volume changes after the mandatory nationwide iodine fortification (IF) program in two Danish areas with different iodine intake at baseline (Copenhagen, mild iodine deficiency (ID) and Aalborg, moderate ID). Design: A longitudinal population-based study (DanThyr). Methods: We examined 2465 adults before (1997) and after (2008) the Danish IF of salt (2000). Ultrasonography was carried out by the same sonographers using the same equipment, after controlling performances. Participants treated for thyroid disease were excluded from analyses. Results: Overall, median thyroid volume had increased in Copenhagen (11.8-12.2 ml, PZ0.001) and decreased in Aalborg, although not significantly (13.3-13.1 ml, PZ0.07) during the 11 years of follow-up. In both regions, there was an age-related trend in individual changes in thyroid volume from baseline to follow-up; thyroid volume increased in women !40 years of age and decreased in women O40 years of age. In a multivariate regression model, higher age at entry was a predictor (P!0.05) for thyroid volume decrease O20% during the follow-up period (women aged 40-45 years: odds ratio (OR) 4.3 (95% CI, 2.2-8.2); women aged 60-65 years: 5.8 (2.9-11.6)) and individuals of higher age were also less likely to have an increase in thyroid volume (women aged 40-45 years: OR 0.2 (0.1-0.3); women aged 60-65: OR 0.3 (0.2-0.4)). Conclusions: Age-dependent differences in thyroid volume and enlargement had leveled out after the Danish iodization program. Thus, the previously observed increase in thyroid volume with age may have been caused by ID.