Background: The aim of this study was to investigate the national prevalence of thyroid dysfunction in Spain and its association with various clinical, environmental, and demographic variables. Methods: The study included 4554 subjects (42.4% men) with a mean age of 50 years (range 18–93 years), who were participants in a national, cross-sectional, population-based survey conducted in 2009–2010. Data gathered included clinical and demographic characteristics, physical examination, and blood sampling. Thyrotropin, free thyroxine, free triiodothyronine, and thyroid peroxidase antibody (TPOAb) concentrations were analyzed by electrochemiluminescence. Urinary iodine (UI) levels were measured in an isolated urine sample. Results: The prevalence of treated hypothyroidism, untreated subclinical hypothyroidism, and untreated clinical hypothyroidism was 4.2% [confidence interval (CI) 3.6–4.9%], 4.6% [CI 4.0–5.2%], and 0.3% [CI 0.1–0.5%], respectively. The prevalence of total hypothyroidism (including all fractions) was 9.1% [CI 8.2–10.0%]. The prevalence of total hyperthyroidism was 0.8% [CI 0.6–1.1]. A total of 7.5% [CI 6.7–8.3%] of the population tested positive for TPOAbs (≥50 IU/mL). In multivariate logistic regression models, TPOAbs were strongly associated with both hypothyroidism ( p < 0.001) and hyperthyroidism ( p = 0.005), whereas high UI levels (>200 μg/g creatinine) were associated with hypothyroidism ( p < 0.001). The positive association between UI and hypothyroidism remained for both treated ( p < 0.001) and untreated ( p < 0.05) hypothyroidism, whereas it was especially significant for non-autoimmune (TPOAbs negative) forms ( p < 0.001). At UI levels ≥200 μg/g, there was a positive correlation between UI and thyrotropin levels (β = 0.152, p < 0.001) and a negative correlation between UI and free triiodothyronine levels (β = −0.134, p = 0.001). Conclusion: According to the data, a large proportion (10%) of the Spanish population has some evidence of thyroid dysfunction. High TPOAb concentrations were associated with both hypo- and hyperthyroidism, whereas high UI concentrations were associated with hypothyroidism.

Objective: To analyze the reference range of thyroid‐stimulating hormone (TSH) in different BMI categories and its impact on the classification of hypothyroidism.Methods: The study included 3,928 individuals free of thyroid disease (without previous thyroid disease, no interfering medications, TSH <10 µUI/mL and thyroid peroxidase antibodies [TPO Abs] <50 IU/mL) who participated in a national, cross‐sectional, population‐based study and were representative of the adult population of Spain. Data gathered included clinical and demographic characteristics, physical examination, and blood and urine sampling. TSH, free thyroxine, free triiodothyronine, and TPO Ab were analyzed by electrochemiluminescence (E170, Roche Diagnostics, Basel, Switzerland).Results: The reference range (p2.5‐97.5) for TSH was estimated as 0.6 to 4.8 µUI/mL in the underweight category (BMI<20 kg/m²), 0.6 to 5.5 µUI/mL in the normal‐weight category (BMI 20‐24.9 kg/m²), 0.6 to 5.5 µUI/mL in the overweight category (BMI 25‐29.9 kg/m²), 0.5 to 5.9 µUI/mL in the obesity category (BMI 30‐39.9 kg/m²), and 0.7 to 7.5 µUI/mL in the morbid obesity category (BMI ≥40). By using the reference criteria for the normal‐weight population, the prevalence of high TSH levels increased threefold in the morbid obesity category (P < 0.01).Conclusions: Persons with morbid obesity might be inappropriately classified if the standard ranges of normality of TSH for the normal‐weight population are applied to them.

Objective The aim of this study was to examine possible associations between ambient temperature and obesity in the Spanish population using an ecological focus. Methods The Di@bet.es study is a national, cross‐sectional, population‐based survey of cardiometabolic risk factors and their association with lifestyle. Sample: 5,061 subjects in 100 clusters. Variables: Clinical, demographic and lifestyle survey, physical examination, and blood sampling. The mean annual temperature (°C) for each study site was collected from the Spanish National Meteorology Agency (1971‐2000). Results The prevalence rates of obesity in the different geographical areas divided according to mean annual temperature quartiles were 26.9% in quartile 1 (10.4‐14.5°C), 30.5% in quartile 2 (14.5‐15.5°C), 32% in quartile 3 (15.5‐17.8°C), and 33.6% in quartile 4 (17.8‐21.3°C) (P = 0.003). Logistic regression analyses including multiple socio‐demographic (age, gender, educational level, marital status) and lifestyle (physical activity, Mediterranean diet score, smoking) variables showed that, as compared with quartile 1, the odd ratios for obesity were 1.20 (1.01‐1.42), 1.35 (1.12‐1.61), and 1.38 (1.14‐1.67) in quartiles 2, 3, and 4, respectively (P = 0.001 for difference, P < 0.001 for trend). Conclusions Our study reports an association between ambient temperature and obesity in the Spanish population controlled for known confounders.

Previous studies have suggested that iron deficiency (ID) may impair thyroid hormone metabolism, however replication in wide samples of the general adult population has not been performed. We studied 3846 individuals free of thyroid disease, participants in a national, cross sectional, population based study representative of the Spanish adult population. Thyroid stimulating hormone (TSH), free thyroxin (FT4) and free triiodothyronine (FT3) were analyzed by electrochemiluminescence (E170, Roche Diagnostics). Serum ferritin was analyzed by immunochemiluminescence (Architect I2000, Abbott Laboratories). As ferritin levels decreased (>100, 30–100, 15–30, <15 µg/L) the adjusted mean concentrations of FT4 (p < 0.001) and FT3 (p < 0.001) descended, whereas TSH levels remained unchanged (p = 0.451). In multivariate logistic regression models adjusted for age, sex, UI, BMI and smoking status, subjects with ferritin levels <30 µg/L were more likely to present hypothyroxinemia (FT4 < 12.0 pmol/L p5): OR 1.5 [1.1–2.2] p = 0.024, and hypotriiodothyroninemia (FT3 < 3.9 pmol/L p5): OR 1.8 [1.3–2.6] p = 0.001 than the reference category with ferritin ≥30 µg/L. There was no significant heterogeneity of the results between men, pre-menopausal and post-menopausal women or according to the iodine nutrition status. Our results confirm an association between ID and hypothyroxinemia and hypotriiodothyroninemia in the general adult population without changes in TSH.