Thyroid Function and Body Weight: A Community-Based Longitudinal Study

OBJECTIVE: Body weight and overt thyroid dysfunction are associated. Cross-sectional population-based studies have repeatedly found that thyroid hormone levels, even within the normal reference range, might be associated with body weight. However, for longitudinal data, the association is less clear. Thus, we tested the association between serum thyrotropin (TSH) and body weight in a community-based sample of adult persons followed for 11 years. METHODS: A random sample of 4,649 persons aged 18-65 years from a general population participated in the DanThyr study in 1997-8. We included 2,102 individuals who participated at 11-year follow-up, without current or former treatment for thyroid disease and with measurements of TSH and weight at both examinations. Multiple linear regression models were used, stratified by sex and adjusted for age, smoking status, and leisure time physical activity. RESULTS: Baseline TSH concentration was not associated with change in weight (women, P = 0.17; men, P = 0.72), and baseline body mass index (BMI) was not associated with change in TSH (women, P = 0.21; men, P = 0.85). Change in serum TSH and change in weight were significantly associated in both sexes. Weight increased by 0.3 kg (95% confidence interval [CI] 0.1, 0.4, P = 0.005) in women and 0.8 kg (95% CI 0.1, 1.4, P = 0.02) in men for every one unit TSH (mU/L) increase. CONCLUSIONS: TSH levels were not a determinant of future weight changes, and BMI was not a determinant for TSH changes, but an association between weight change and TSH change was present

Thyroid Nodules in an 11-Year DanThyr Follow-Up Study

Context: Limited longitudinal data are available on changes in the thyroid gland structure in a population and how this is influenced by iodine fortification (IF). Objective: Our objective was to clarify how IF influenced thyroid gland structure in 2 regions with different iodine intake at baseline (Copenhagen, mild iodine deficiency [ID]; Aalborg, moderate ID). Design and Setting: We conducted a longitudinal population-based study (DanThyr) where participants were examined before (1997) and after (2008) the Danish mandatory IF of salt (2000). Participants: We examined 2465 adults, and ultrasonography was performed by the same sonographers using the same equipment, after controlling performances. Main Outcome Measure: Change in thyroid gland structure was evaluated. Results: The follow-up period saw an increased prevalence of multinodularity (9.8%–13.8 %, P &amp;lt; .001), especially in the previously moderate ID region of Aalborg (9.1%–15.4%, P &amp;lt; .001), whereas no change in prevalence was seen for solitary nodules (5.6%–5.1%, P = .34). In individual participants, changes in thyroid structure and disappearance of thyroid nodules during the 11 years was common with an overall normalization rate of 21.2 (95% confidence interval [CI] = 17.9–24.9) per 1000 person-years. Solitary nodules had a significantly higher normalization rate than multiple nodules (normalization rate ratio 0.47 [95% CI = 0.32–0.67]). A regional difference (Aalborg vs Copenhagen) was seen between normalization rates of multiple nodules (normalization rate ratio 0.29 [95% CI = 0.12–0.64]), but not for solitary nodules (normalization rate ratio 0.81 [95% CI = 0.53–1.21]). Conclusions: Changes in the thyroid gland structure with both appearance and disappearance of thyroid nodules are common after an iodization program. </jats:sec

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

ObjectiveTo 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).DesignA longitudinal population-based study (DanThyr).MethodsWe 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.ResultsOverall, median thyroid volume had increased in Copenhagen (11.8–12.2 ml, P=0.001) and decreased in Aalborg, although not significantly (13.3–13.1 ml, P=0.07) 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 &lt;40 years of age and decreased in women &gt;40 years of age.In a multivariate regression model, higher age at entry was a predictor (P&lt;0.05) for thyroid volume decrease &gt;20% 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)).ConclusionsAge-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.</jats:sec

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

ObjectiveOur objective was to investigate individual serum thyroglobulin (Tg) changes in relation to iodine fortification (IF) and to clarify possible predictors of these changes.DesignWe 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.MethodsWe 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.ResultsOverall, the follow-up period saw no change in median Tg in Copenhagen (9.1/9.1 μg/l,P=0.67) while Tg decreased significantly in Aalborg (11.4/9.0 μg/l,P&lt;0.001). Regional differences were evident before IF (Copenhagen/Aalborg, 9.1/11.4 μg/l,P&lt;0.001), whereas no differences existed after IF (9.1/9.0 μg/l,P=1.00). Living in Aalborg (P&lt;0.001) and not using iodine supplements at baseline (P=0.001) predicted a decrease in Tg whereas baseline thyroid enlargement (P=0.02) and multinodularity (P=0.01) were associated with an individual increase in Tg during follow-up.ConclusionsAfter 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.</jats:sec

Iodine excretion has decreased in Denmark between 2004 and 2010 - the importance of iodine content in milk

Fortification with the essential trace element iodine is widespread worldwide. In the present study, results on iodine excretion and intake of iodine-rich foods from a cross-sectional study carried out in 2004–5, 4 to 5 years after the implementation of mandatory iodine fortification, were compared with data in a study carried out in 2008–10. The 2008–10 study was a follow-up of a cross-sectional study carried out before iodine fortification was implemented. Participants in the cross-sectional studies were randomly selected. Both studies were carried out in the cities of Aalborg and Copenhagen in Denmark. The median urinary iodine concentration decreased in women from 97 μg/l (n 2862) to 78 μg/l (n 2041) (P&lt; 0·001). The decrease persisted after adjustment for age, city and education, and if expressed as estimated 24 h iodine excretion. The prevalence of users of iodine containing dietary supplements increased from 29·4 to 37·3 % (P&lt; 0·001). The total fluid intake increased in women (P&lt; 0·001), but the intake of other iodine-rich foods did not change. The median urinary iodine concentration did not change in men (114 μg/l (n 708) and 107 μg/l (n 424), respectively), while the total fluid intake decreased (P= 0·001). Iodine content was measured in milk sampled in 2000–1 and in 2013. The iodine content was lower in 2013 (12 (sd 3) μg/100 g) compared with that in 2000–1 (16 (sd 6) μg/100 g) (P&lt; 0·001). In conclusion, iodine excretion in women has decreased below the recommended level. The reason might probably, at least partly, be a decreased content of iodine in milk.</jats:p