Ilze Konrade

Background/Objectives: Psoriasis and Hashimoto’s thyroiditis are chronic immune-mediated disorders affecting distinct target organs but sharing overlapping pathogenic mechanisms, including gut dysbiosis, impaired intestinal barrier function, and systemic immune dysregulation. Growing evidence highlights the gut–skin and gut–thyroid axes as important interfaces linking microbial alterations to immune-mediated inflammation. This review aims to synthesize current knowledge on gut microbiota alterations in psoriasis and Hashimoto’s thyroiditis, with particular emphasis on intestinal permeability, immune pathways, and microbiome-derived metabolites. Methods: A narrative review of experimental and human observational studies was conducted to evaluate evidence on gut microbiota composition, intestinal barrier integrity, immune regulation, bile acid metabolism, and dietary influences in psoriasis and Hashimoto’s thyroiditis. The relevant literature examining mechanistic pathways and clinical associations was included. Results: Both conditions are associated with altered gut microbial composition, including reduced abundance of short-chain fatty acid–producing taxa, which may impair epithelial barrier integrity and promote systemic immune activation. Increased intestinal permeability and enhanced Th17-driven inflammatory responses are reported in both diseases. Recent studies suggest that dysregulated bile acid metabolism may influence intestinal permeability and immune balance along the gut–skin–thyroid axis, although direct clinical data remain limited. Dietary patterns, particularly anti-inflammatory and Mediterranean diets, are consistently associated with increased microbial diversity, improved metabolic profiles, and reduced systemic inflammation. However, most human evidence is observational. Conclusions: The gut microbiome represents a potential mechanistic link connecting diet, intestinal barrier function, immune regulation, and organ-specific autoimmunity in psoriasis and Hashimoto’s thyroiditis. While microbiome-targeted interventions show biological plausibility, well-designed, mechanistically informed randomized controlled trials are required to establish causality and clinical relevance.

Thyroid diseases are common and highly heritable. Under the Global Biobank Meta-analysis Initiative, we performed a meta-analysis of genome-wide association studies from 19 biobanks for five thyroid diseases: thyroid cancer, benign nodular goiter, Graves’ disease, lymphocytic thyroiditis, and primary hypothyroidism. We analyzed genetic association data from ∼2.9 million genomes and identified 235 known and 501 novel independent variants significantly linked to thyroid diseases. We discovered genetic correlations between thyroid cancer, benign nodular goiter, and autoimmune thyroid diseases ( r ² =0.21-0.97). Telomere maintenance genes contribute to benign and malignant thyroid nodular disease risk, whereas cell cycle, DNA repair, and DNA damage response genes are predominantly associated with thyroid cancer. We proposed a paradigm explaining genetic predisposition to benign and malignant thyroid nodules. We evaluated thyroid cancer polygenic risk scores (PRS) for clinical applications in thyroid cancer diagnosis. We found PRS associations with thyroid cancer risk features: multifocality, lymph node metastases, and extranodal extension.

Elevated plasma levels of trimethylamine N-oxide (TMAO) have been proposed as a diet-derived biomarker of cardiometabolic disease risk. Caloric restriction is the most common dietary intervention used to improve cardiometabolic health; however, novel trends suggest a fasting-mimicking diet (FMD) as a more feasible alternative. FMD is a variation of intermittent fasting, based on caloric restriction and limitation of protein sources of animal origin, applied in daily cycles during a 5-day period. As TMAO is intensively produced by gut microbiota after the consumption of animal-derived products, we aim to investigate whether a 5-day FMD affects plasma TMAO levels and markers of metabolic health. To investigate whether an increase in vegetable intake possesses similar effects on TMAO levels and metabolic parameters, healthy volunteers (n = 24) were subjected to a 5-day FMD and 19 volunteers served as a reference group (VEG). This group of volunteers consumed an additional four servings of vegetables per day, but otherwise stayed on their usual diet. FMD resulted in a twofold decrease in plasma TMAO levels, which was not evident in the volunteers from the VEG group. Moreover, FMD led to a weight loss of 2.8 ± 0.2 kg and a subsequent reduction in BMI compared to baseline. The FMD group exhibited a significant elevation in plasma ketone bodies (14-fold compared to baseline) and a decrease in IGF-1 levels by 37 ± 8 ng/mL. Since fasting glucose and C-peptide levels decreased, all volunteers in the FMD group showed improved insulin sensitivity and a decreased HOMA-IR index. In contrast, in the VEG group, only a slight reduction in plasma levels of fasting glucose and triglycerides was noted. In conclusion, we show that FMD is a viable strategy to reduce plasma levels of TMAO by limiting caloric intake and animal-derived protein consumption. The reduction in the level of TMAO could be an additional benefit of FMD, leading to a reduced risk of cardiometabolic diseases.

Background and Objectives: Adequate dietary intake of iodine and selenium is essential during pregnancy. While iodine is vital for maternal thyroid function and fetal development, selenium contributes to the regulation of thyroid function and thyroid autoimmunity. This study aimed to assess the consumption of iodine- and selenium-containing products by women of reproductive age and the iodine and selenium nutritional status of pregnant women in Latvia. Materials and Methods: Population health survey (2010–2018) data were used to characterize dietary habits in women of reproductive age. Additionally, 129 pregnant women in the first trimester were recruited; they completed a questionnaire and were tested for thyroid function, urinary iodine concentration (UIC), and serum selenium and selenoprotein P levels. Results: The use of some dietary sources of iodine (e.g., milk and dairy products) and selenium (e.g., bread) has decreased in recent years. Less than 10% of respondents reported the use of iodized salt. The use of supplements has become more common (reported by almost 50% of respondents in 2018). Dietary habits were similar in pregnant women, but the use of supplements was even higher (almost 70%). Nevertheless, most supplements used in pregnancy had insufficient contents of iodine and selenium. Thyroid function was euthyreotic in all women, but 13.9% of participants had a thyroid peroxidase antibodies (TPO-ab) level above 60 IU/mL. The median UIC (IQR) was 147.2 (90.0–248.1) μg/gCr, and 52.8% of pregnant women had a UIC below 150 μg/gCr. The mean selenium (SD) level was 101.5 (35.6) μg/L; 30.1% of women had a selenium level below 80 μg/L. The median selenoprotein P level was 6.9 (3.1–9.0) mg/L. Conclusions: Iodine nutrition in Latvian population of pregnant women was near the lower limit of adequate and a third of the population had a selenium deficiency. Supplements were frequently used, but most did not contain the recommended amounts of iodine and selenium.