Objective: We evaluated correlations of occupational physical activity (OPA) and recreational exercise (RE), respectively, with thyroid function in patients with Hashimoto’s thyroiditis (HT). Methods: We included 438 individuals with clinically diagnosed HT. Information on OPA and RE were collected through a self-report questionnaire. We assessed correlations between clinical phenotypes (TSH, T3, T4, fT4, TgAb, TPOAb, thyroid volume, vitamin D) and physical activities (OPA and RE) in all HT patients (ALL) and in two severity-based subgroups of patients (MILD and OVERT). Results: The main novel findings are significant correlations between increase in OPA and (i) a decrease in fT4 (OVERT, r = −0.265, p = 0.0002 and ALL, r = −0.138, p = 0.006); (ii) an increase in TSH (ALL, r = 0.124, p = 0.014 and OVERT, r = 0.183, p = 0.013) and (iii) an increase in TPOAb antibodies (ALL, r = 0.101, p = 0.045). In contrast, we observed correlations between increase in RE and: (i) a decrease in TSH (OVERT, r = −0.238, p = 0.001); (ii) a decrease in TgAb antibodies (OVERT, r = −0.194, p = 0.01) and (iii) an increase in vitamin D levels (ALL, r = 0.146, p = 0.005 and OVERT, r = 0.173, p = 0.023). Conclusions: Our results suggest that, unlike RE, OPA correlates with decreased thyroid function and increased thyroid autoimmunity. Our study proposes that the PA health paradox also applies for the thyroid health.

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.

Background/Objectives: Multigenerational families with unusually early disease onset provide a unique opportunity to investigate the genetic architecture underlying the missing heritability of complex diseases. Here, we investigated the genetic basis of apparent autosomal dominant early-onset Hashimoto’s thyroiditis (HT) in a multigenerational pedigree using whole-exome sequencing (WES) in 9 individuals and PacBio HiFi long-read whole-genome sequencing (LR-WGS) in four family members spanning three generations. Methods: WES identified a rare disease-segregating TPH2 missense variant, while LR-WGS identified approximately 2000 structural variants (SVs) shared by the three sequenced affected relatives and absent from the unaffected father. Results: Affected-lineage-shared SVs were significantly enriched within established hypothyroidism GWAS loci (447 observed vs. 292.6 expected overlaps; p = 6.99 × 10⁻⁴), with prominent clusters at the NFATC1-ATP9B and PDCD6-AHRR loci. Integrative analyses incorporating regulatory annotation, GWAS overlap, and exploratory proteomic profiling highlighted candidate regulatory SVs affecting enhancers and long non-coding RNAs within the TPH2/TRHDE, TPO/LALTOP, and TSHR loci. Exploratory proteomic profiling was consistent with involvement of the NFATC1-ATP9B and PDCD6-AHRR loci and identified AXIN1 as an additional candidate locus. Parallel polygenic risk score (PRS) analysis showed that the three affected sequenced family members ranked above the 95th percentile of the HT PRS distribution. Conclusions: Together, these findings are consistent with a multi-hit genetic model in which elevated polygenic burden and multiple regulatory structural variants may jointly contribute to early-onset familial HT. The observed enrichment of affected-lineage-shared SVs within established hypothyroidism GWAS loci further suggests that regulatory structural variation may contribute to previously unexplained non-coding genetic susceptibility.

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 (CROHT), 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.

Background/Objectives: Vitamin D is an important regulator of immune and inflammatory processes, while its deficiency is frequently observed in Hashimoto’s thyroiditis (HT). The relationship between Vitamin D and systemic inflammation in HT remains insufficiently understood, particularly across different disease stages. Methods: We used the Olink Target 96 Inflammation panel to investigate this association. Inflammatory proteins and serum 25(OH)D levels were measured in 257 HT patients and 173 controls from the CROHT biobank. Participants were categorized as Vitamin D deficient (<20 ng/mL) or non-deficient (≥20 ng/mL), with HT patients further stratified as euthyroid, hypothyroid, or levothyroxine-treated. Associations between 25(OH)D and 92 inflammatory proteins were assessed using multivariable linear regression adjusted for age, sex, BMI, smoking, and season of blood sampling, followed by interaction testing and meta-analysis. Results: Vitamin D deficiency was prevalent in both HT patients and controls. Among Vitamin D-deficient HT patients, higher 25(OH)D levels showed nominal inverse associations with the previously reported HT-associated inflammatory proteins IL-17C, CCL20, and CCL11, as well as with GDNF. Among non-deficient HT patients, a nominal positive association with CD6 was observed. None of these associations or interaction terms remained statistically significant after false discovery rate correction. Conclusions: These findings should therefore be considered exploratory and hypothesis-generating. Nevertheless, the observed Vitamin D status-specific patterns suggest that the relationship with inflammatory profiles in HT may differ according to Vitamin D status and warrant validation in prospective and mechanistic studies.