van Vliet NA, Kamphuis AEP, den Elzen WPJ, et al. - While a self-reported clinical diagnosis of hypothyroidism was linked to a greater risk of anemia [defined as hemoglobin level of <13 g/dL in men and <12 g/dL in women], no evidence of a causal relationship with variations in thyroid function within the euthyroid range was found. Thyroid hormone intracellular regulation, on the other hand, may play a function in the development of anemia.

• It was a cross-sectional and Mendelian Randomization study.

• The sample consisted of 445,482 candidates, mean age of 56.77 years (SD 8.0) and 54.2% were women.

• Self-reported clinical diagnoses of hypo- and hyperthyroidism were related to a greater risk of anemia in cross-sectional logistic regression studies, however with large confidence intervals for hyperthyroidism.

• They found no link between greater or lower genetically influenced thyrotropin and anemia, nor between higher or lower genetically influenced free thyroxine and anemia.

• Individuals with genetic variants in the DIO3OS gene, which is involved in the intracellular regulation of thyroid hormones, were at a greater risk of anemia; no association was seen with variants in the DIO1 or DIO2 genes.