Dr. Ron’s Research Review – December 8, 2010

This week’s research review contains information on hypothyroidism.

Subclinical hypothyroidism: an update for primary care physicians (Fatourechi 2009)

Subclinical hypothyroidism (SCH), also called mild thyroid failure, is diagnosed when peripheral thyroid hormone levels are within normal reference laboratory range but serum thyroid-stimulating hormone (TSH) levels are mildly elevated. This condition occurs in 3% to 8% of the general population. It is more common in women than men, and its prevalence increases with age. Of patients with SCH, 80% have a serum TSH of less than 10 mIU/L. The most important implication of SCH is high likelihood of progression to clinical hypothyroidism.

Thyroid hormone replacement: an iatrogenic problem (O'Reilly 2010)

The published literature shows that the serum TSH concentration is a poor indicator of clinical status in patients on thyroxine. The adequacy of thyroxine replacement should be assessed clinically with the serum T3 being measured, when required, to detect over-replacement.

Multiple metals predict prolactin and thyrotropin (TSH) levels in men (Meeker, Rossano et al. 2009)

Lead and copper were associated with non-monotonic decrease in TSH, while arsenic was associated with a dose-dependent increase in TSH.

Hypothyroidism Mimics Require Consideration (Pritchard 2008)

Eric Pritchard makes the point that many patients appear to be suffering from “thyroid” deficiencies when, in fact, they are suffering from replaceable post-thyroid hormone deficiencies, i.e., deficiencies of peripheral metabolism of T4 to T3 or the reception and use of T3 by cells and their nuclei.

Dr. Ron


Articles

Subclinical hypothyroidism: an update for primary care physicians

         (Fatourechi 2009) Download

Subclinical hypothyroidism (SCH), also called mild thyroid failure, is diagnosed when peripheral thyroid hormone levels are within normal reference laboratory range but serum thyroid-stimulating hormone (TSH) levels are mildly elevated. This condition occurs in 3% to 8% of the general population. It is more common in women than men, and its prevalence increases with age. Of patients with SCH, 80% have a serum TSH of less than 10 mIU/L. The most important implication of SCH is high likelihood of progression to clinical hypothyroidism. The possibility that it is a cardiovascular risk factor has been a subject of debate. Large-scale randomized studies are needed for evidence-based recommendations regarding screening for mild thyroid failure and levothyroxine therapy for this condition. Currently, the practical approach is routine levothyroxine therapy for persons with a persistent serum TSH of more than 10.0 mIU/L and individualized therapy for those with a TSH of less than 10.0 mIU/L.

Thyroid hormone replacement: an iatrogenic problem

            (O'Reilly 2010) Download

The published literature shows that the serum TSH concentration is a poor indicator of clinical status in patients on thyroxine. The adequacy of thyroxine replacement should be assessed clinically with the serum T3 being measured, when required, to detect over-replacement.

Hypothyroidism Mimics Require Consideration

(Pritchard 2008) Download

Multiple metals predict prolactin and thyrotropin (TSH) levels in men

         (Meeker, Rossano et al. 2009) Download

Exposure to a number of metals can affect neuroendocrine and thyroid signaling, which can result in adverse effects on development, behavior, metabolism, reproduction, and other functions. The present study assessed the relationship between metal concentrations in blood and serum prolactin (PRL) and thyrotropin (TSH) levels, markers of dopaminergic, and thyroid function, respectively, among men participating in a study of environmental influences on male reproductive health. Blood samples from 219 men were analyzed for concentrations of 11 metals and serum levels of PRL and TSH. In multiple linear regression models adjusted for age, BMI and smoking, PRL was inversely associated with arsenic, cadmium, copper, lead, manganese, molybdenum, and zinc, but positively associated with chromium. Several of these associations (Cd, Pb, Mo) are consistent with limited studies in humans or animals, and a number of the relationships (Cr, Cu, Pb, Mo) remained when additionally considering multiple metals in the model. Lead and copper were associated with non-monotonic decrease in TSH, while arsenic was associated with a dose-dependent increase in TSH. For arsenic these findings were consistent with recent experimental studies where arsenic inhibited enzymes involved in thyroid hormone synthesis and signaling. More research is needed for a better understanding of the role of metals in neuroendocrine and thyroid function and related health implications.


References

Fatourechi, V. (2009). "Subclinical hypothyroidism: an update for primary care physicians." Mayo Clin Proc 84(1): 65-71.

Meeker, J. D., M. G. Rossano, et al. (2009). "Multiple metals predict prolactin and thyrotropin (TSH) levels in men." Environ Res 109(7): 869-73.

O'Reilly, D. S. (2010). "Thyroid hormone replacement: an iatrogenic problem." Int J Clin Pract 64(7): 991-4.

Pritchard, E. K. (2008). "Hypothyroidism Mimics Require Consideration." from http://www.tpa-uk.org.uk/pritchard2_mimics.pdf.