Iron deficiency is shown to significantly reduce T4 to T3 conversion, increase reverse T3 levels, and block the thermogenic (metabolism boosting) properties of thyroid hormone (238-242). Thus, iron deficiency, as indicated by an iron saturation below 25 or a ferritin below 70, will result in diminished intracellular T3 levels. Additionally, T4 should not be considered adequate thyroid replacement if iron deficiency is present (238,239,241,242).
Inflammation associated with common conditions
The inflammatory cytokines IL-1, Il-6, C-reactive protein (CRP), and TNF-alpha will significantly decrease D1 activity and reduce tissue T3 levels (105-113). Any person with an inflammatory condition — including physical or emotional stress (243-248), obesity (248-252), diabetes (248,249,253), depression (254-257), menopause (surgical or natural) (258), heart disease (248,259,260), autoimmune disease (lupus, Hashimoto’s, multiple sclerosis, arthritis, etc) (114,115,164,265), injury (266), chronic infection (261,262) or cancer (267-269) — will have a decreased T4 to T3 conversion in the body and a relative tissue hypothyroidism. The inflammatory cytokines will, however, increase the activity of D2 and suppress the TSH despite reduced peripheral T3 levels; again, making a normal TSH an unreliable indicator of normal tissue thyroid levels (105-113)
There is a direct inverse correlation between CRP and reduced tissue T3 (112,270), so individuals with elevated CRP (greater than 3 mg/l) or other inflammatory cytokines will have a significant reduction in cellular T3 levels. The suppression of intracellular T3 levels correlates with the degree of elevation of CRP, despite serum thyroid tests being “normal” (112,270). Thus, if any inflammation is present, which is found in numerous clinical and subclinical conditions (as above), the body will have lower cellular T3 levels that are often inadequate for optimal functioning; but the pituitary will have increased levels of T3, resulting in a lowering of the TSH that would potentially be inappropriately interpreted as an indication of “normal” thyroid levels.
cont on nahypothyroidism.org/deiodi...