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Food is considered as important environmental factor that plays a role in development of Hashimoto's thyroiditis (HT). The goal of our study was to identify food groups, assessed by food frequency questionnaire, that differ in consumption frequency between 491 patients with HT and 433 controls. We also analysed association of food groups with the wealth of HT-related clinical traits and symptoms. We found significantly increased consumption of animal fat (OR 1.55, p  < 0.0001) and processed meat (OR 1.16, p  = 0.0012) in HT cases, whereas controls consumed significantly more frequently red meat (OR 0.80, p  < 0.0001), non-alcoholic beverages (OR 0.82, p  < 0.0001), whole grains (OR 0.82, p  < 0.0001) and plant oil (OR 0.87, p  < 0.0001). We also observed association of plant oil consumption with increased triiodothyronine levels in HT patients (β = 0.07, p  < 0.0001), and, association of olive oil consumption with decreased systolic blood pressure (β = − 0.16, p  = 0.001) in HT patients on levothyroxine (LT4) therapy. Analysis of food consumption between HT patients with and without LT4 therapy suggest that patients do not tend to modify their diet upon HT diagnosis in our population. Our study may be of relevance to nutritionists, nutritional therapists and clinicians involved in developing dietary recommendations for HT patients.

In this cross-sectional observational study, we investigated whether recreational exercise (RE) influences systemic inflammation in Hashimoto’s thyroiditis (HT) across different disease severity groups. We analyzed 403 participants from the Croatian Biobank of Patients with HT (CRO-HT), including 173 controls and 230 HT patients (euthyroid, levothyroxine [LT4]-treated, and hypothyroid). Serum levels of 92 inflammatory proteins were measured using the Olink® Target 96 Inflammation panel, and exercise status was assessed via structured questionnaires. Linear regression revealed distinct protein associations depending on thyroid status. In controls, RE was associated with reduced MMP-10 and FGF-5, reflecting cardiovascular and muscle benefits. In euthyroid patients, RE was associated with decreased CXCL9 and TRAIL, implicating reduced type 1 inflammation and vascular risk. LT4-treated patients showed increases in IL-15RA and IL-24 with RE, suggesting improved muscle metabolism and anti-inflammatory effects. In hypothyroid patients, RE was associated with reduced CCL20 and increased HGF, while changes in TRANCE and TWEAK indicated mixed effects on bone and immune regulation. Notably, RE was associated with reduced CXCL9 and CCL20, two proteins previously linked to HT risk. Overall, RE is associated with distinct changes in inflammatory profiles across HT disease severity groups, with the most favourable responses observed in LT4-treated patients, suggesting synergy with hormone therapy.

The aims of this study were to evaluate: (1) associations of vitamin D with the presence/severity of Hashimoto’s thyroiditis (HT) and (2) correlations of vitamin D with thyroid-related phenotypes. Total 25(OH)D (vitamin D in the text) was measured from stored serum samples of 461 HT patients and 176 controls from a Croatian Biobank of HT patients (CROHT). (1) Vitamin D levels, and proportions of vitamin D deficiency, were compared between HT cases and controls. HT patients were additionally divided into two groups (MILD and OVERT) to take into account HT severity. (2) Correlations between vitamin D and 10 clinical phenotypes in all HT patients and two subgroups of HT patients were tested using the Spearman correlation test. Our analyses were adjusted for age, gender, BMI, smoking status and seasonality of blood sampling. (1) No significant differences in vitamin D levels, or proportions of vitamin D deficiency, were detected between HT patients of all disease stages and controls. However, a nominally significant difference in vitamin D levels between MILD and OVERT subgroups (OR = 1.038, p = 0.023) was observed. Proportions of individuals with vitamin D deficiency during winter–spring were high: all HT cases (64.69%), MILD (60.64%), OVERT (68.7%), controls (60.79%). (2) A nominally significant negative correlation between vitamin D and TSH in all HT patients (r = −0.113, p = 0.029) and a positive correlation between vitamin D and systolic blood pressure in OVERT HT patients (r = 0.205, p = 0.025) were identified. Our study indicates that there is no association between vitamin D and HT; however, there may be a subtle decrease in vitamin D levels associated with overt hypothyroidism.

Thyroid hormones (THs) are key regulators of cellular growth, development, and metabolism. The thyroid gland secretes two THs, thyroxine (T4) and triiodothyronine (T3), into the plasma where they are almost all bound reversibly to plasma proteins. Free forms of THs are metabolically active, however, they represent a very small fraction of total TH levels. No genome-wide studies have been performed to date on total TH levels, comprising of protein-bound and free forms of THs. To detect genetic variants associated with total TH levels, we carried out the first GWAS meta-analysis of total T4 levels in 1121 individuals from two Croatian cohorts (Split and Korcula). We also performed GWAS analyses of total T3 levels in 577 individuals and T3/T4 ratio in 571 individuals from the Split cohort. The top association in GWAS meta-analysis of total T4 was detected for an intronic variant within SLC22A9 gene (rs12282281, P = 4.00 × 10 ). Within the same region, a genome-wide significant variant (rs11822642, P = 2.50 × 10 ) for the T3/T4 ratio was identified. SLC22A9 encodes for an organic anion transporter protein expressed predominantly in the liver and belongs to the superfamily of solute carriers (SLC), a large group of transport membrane proteins. The transport of THs across the plasma membrane in peripheral tissues is facilitated by the membrane proteins, and all TH transport proteins known to date belong to the same SLC superfamily as SLC22A9. These results suggest a potential role for SLC22A9 as a novel transporter protein of THs.

Thyroid dysfunction appears to be the leading endocrine disorder. We conducted a cross-sectional study on 4402 individuals from three Croatian cohorts. The aim of this study was to analyse the prevalence of diagnosed and undiagnosed hypothyroidism, hyperthyroidism (subclinical and clinical) and positive thyroid antibodies in the Croatian population. The results of the study indicated that 17.6% of participants were euthyroid with positive antibodies. The prevalence of clinical and subclinical hypothyroidism was 3% and 7.4%, respectively, while the prevalence of clinical and subclinical hyperthyroidism was 0.2% and 1.1%, respectively. Among them, 92.6% subclinical hypothyroid, 93.9% clinical hypothyroid, 83% subclinical hyperthyroid and 71.4% clinical hyperthyroid participants were undiagnosed. Finally, the prevalence of undiagnosed subclinical and clinical hypothyroidism in our population was 6.9% and 2.8%, respectively, while the prevalence of undiagnosed subclinical and clinical hyperthyroidism was 0.9% and 0.1%, respectively. Women showed a higher prevalence of thyroid disorders; 1.57 times higher odds of euthyroidism with positive antibodies, 2.1 times higher odds of subclinical hyperthyroidism, 2.37 times higher odds of clinical hypothyroidism and 1.58 times higher odds of subclinical hypothyroidism than men. These results indicate an extremely high proportion of undiagnosed cases, and therefore require investments in a prevention programme.

During development, thyroid hormones play an important role in eye development, while in adults, some pathological thyroid conditions can affect the normal functioning of the eyes. Thyroid eye disease is the most well-known eye pathology caused by a pathological thyroid condition. Few studies have investigated the association between ocular parameters and thyroid function. Thus, in this study, we aimed to examine whether thyroid activity affects ocular parameters. This cross-sectional study included 4633 healthy adults recruited within the 10,001 Dalmatians project of the Croatian Biobank. The plasma levels of thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), thyroglobulin (Tg), thyroglobulin antibodies (TgAb), and thyroid peroxidase antibodies (TPOAb) were measured by an immunoassay. We determined 20 ocular parameters for each participant (10 for each eye, including corneal radius, corneal thickness, anterior chamber depth, anterior chamber angle, lens thickness, posterior chamber length, axial length, intraocular lens power (IOL), spherical power, and cylinder power). Patients with hyperthyroidism had thicker corneas compared to euthyroid individuals. Corneal thickness was also negatively associated with plasma TSH levels. Intra-ocular lens power was higher in patients with clinical hypothyroidism, while spherical power was higher in euthyroid individuals with positive antibodies compared to euthyroid individuals. Intra-ocular lens power negatively correlated with fT4 levels, while spherical power positively correlated with TgAb, TPOAb, and Tg levels and negatively correlated with TSH levels. The anterior chamber angle was positively associated with plasma TSH levels and TPOAb levels and negatively associated with plasma fT4 levels. These findings suggest an interesting interplay between ophthalmic measures and thyroid status, detectable even in the general adult population.

Background Parathyroid hormone (PTH) is one of the principal regulators of calcium homeostasis. Although serum PTH level is mostly accounted by genetic factors, genetic background underlying PTH level is insufficiently known . Therefore, the aim of this study was to identify novel genetic variants associated with PTH levels. Methods We performed GWAS meta-analysis within two genetically isolated Croatian populations followed by replication analysis in a Croatian mainland population and we also combined results across all three analyzed populations. The analyses included 2596 individuals. A total of 7,411,206 variants, imputed using the 1000 Genomes reference panel, were analysed for the association. In addition, a sex-specific GWAS meta-analyses were performed. Results Polymorphisms with the lowest P -values were located on chromosome 4 approximately 84 kb of the 5′ of RASGEF1B gene. The most significant SNP was rs11099476 ( P  = 1.15 × 10 −8 ). Sex-specific analysis identified genome-wide significant association of the variant rs77178854, located within DPP10 gene in females only ( P  = 2.21 × 10 − 9 ). There were no genome-wide significant findings in the meta-analysis of males. Conclusions We identified two biologically plausible novel loci associated with PTH levels, providing us with further insights into the genetics of this complex trait.

Background The primary aim of this study is to gain insights into the immunopathogenesis of the most common autoimmune thyroid disorder, Hashimoto’s thyroiditis (HT). A secondary aim is to identify reliable protein biomarkers that can aid in the prediction of the presence and progression of HT, thus advancing disease monitoring and therapeutic development. Methods This cross-sectional study included 440 individuals − 267 HT patients and 173 healthy controls. HT patients were stratified based on disease severity into two subgroups: euthyroid/levothyroxine-treated (EUTHY-LT4) and hypothyroid (HYPO). Serum levels of 92 inflammation-related proteins were measured using the state-of-the-art Olink proteomics platform. Group comparisons were conducted using ANOVA and post hoc tests to identify differentially expressed proteins. The Boruta machine learning algorithm was applied to identify protein predictors of disease presence and severity. Results A total of 42 differentially expressed proteins were identified, revealing eight distinct expression patterns based on their direction of regulation across comparisons. IL-17C and CCL19 were the most upregulated in HT patients, and ST1A1, CASP-8, CXCL1, SIRT2, and LAP TGF-beta-1 were the most downregulated. An increased IL-17C/IL-10 ratio correlated with disease severity. Additionally, machine learning identified 22 protein markers with potential for distinguishing HT patients from controls, and 7 proteins for differentiating EUTHY-LT4 from HYPO patients. Conclusions Our findings provide novel insights into the molecular landscape of immune-related protein changes in HT, highlighting a dynamic inflammatory response that varies with disease progression. These findings may contribute to the development of biomarkers for patient stratification, improved disease management, and targeted therapies to prevent or delay hypothyroidism.

Thyroid hormones (THs) play an indispensable role in skeletal development and bone remodeling. Some studies have reported associations of THs with serum osteocalcin (OC) levels, but the results are quite inconsistent and the molecular mechanism of their simultaneous or interdependent activity on bone is almost unknown. Therefore, the aim of this study was to determine the possible associations of plasma THs with plasma OC levels and the possible mediating effect of OC on the relationship between THs and bone mineral density (BMD). For this purpose, out of the initial 1981 participants, we selected healthy euthyroid participants controlled for available confounding factors that can affect thyroid function and bone metabolism (N = 694). Given our results, we could not confirm any associations of THs with plasma OC levels nor the mediating effect of OC on the relationship between THs and BMD in euthyroid population. In the group of women controlled for menopause status (N = 396), we found a significant negative association of body mass index (BMI) with OC levels (β = −0.14, p = 0.03). We also found a negative association of free triiodothyronine (fT3) (β = −0.01, p = 0.02) and age (β = −0.003, p < 0.001) with BMD, and a positive association of BMI (β = 0.004, p < 0.001) and male gender (β = 0.1, p < 0.001) with BMD. In addition, we found significantly higher plasma OC levels and lower values of BMD in postmenopausal euthyroid women compared with premenopausal euthyroid women. In our opinion, the results of previous studies suggesting an association between circulating THs and serum OC levels may be influenced by an inconsistent selection of participants and the influence of confounding factors.

•This is the first study of a comprehensive set of dietary factors associated with thyroid hormone levels.•We observed a negative effect of foods with a high glycemic index on thyroid function.•We observed a positive effect of foods with high protein concentration on thyroid function.•We observed a positive effect of frequent consumption of foods rich in saturated fatty acids on thyroid function. The aim of the study was to analyze the association of dietary groups (groups of food items) with thyroid hormone levels in healthy individuals. This cross-sectional study enrolled 4585 healthy individuals from the Dalmatian region of south Croatia with measurements of plasma free triiodothyronine (fT3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) levels. Dietary intake was assessed according to data of the completed food frequency questionnaire, containing 58 food items. Principal component analysis was performed to reduce food items into dietary groups, followed by linear regression analyses to test the association between dietary groups and fT3, fT4, and TSH levels. Among the 4585 healthy individuals, we observed lower plasma fT3 and fT4 levels and higher TSH levels in women than in men. Smokers were found to have significantly lower TSH levels than non-smokers and ex-smokers, and participants with higher fasting glucose levels had higher fT4 levels. Different dietary groups (factors) showed association with fT3, fT4, and TSH levels. It was observed that dietary factors (with frequent consumption of fruit juices, Cedevita vitamin drink, and non-alcoholic drinks) that negatively affected TSH levels simultaneously had a positive effect on fT4, satisfying the expected pattern of effects. In our study, frequent consumption of foods with a high glycemic index showed a positive association with fT3 and fT4 levels and a negative association with TSH levels, whereas foods rich in saturated fatty acids and with a high protein concentration showed a negative association with fT3 and fT4 levels. [Display omitted]