NAS Report: Comment 3 - TSH Reference Values

Comments on the 2006 NAS/NRC report

NAS Report: Comment 3 - TSH Reference Values

Postby admin » Mon Apr 03, 2006 4:39 am

Posted: 31 Mar 2006 08:11 am
Post subject: NAS Report: Comment 3 - TSH Reference Values

Comments on the NAS Report: Fluoride in Drinking Water: A Scientific Review of EPA's Standards

The NAS used TSH reference values which are 4 years out of date

BACKGROUND:

TSH tests are used to assess thyroid function.

In 2002, the National Academy of Clinical Biochemistry (NACB), part of the Academy of the American Association for Clinical Chemistry (AACC), lowered the upper TSH reference limit from 5.0 mIU/L to 3.0 mIU/L, stating that the goal should be 2.5 mIU/L.

This was done because studies had found that the majority (>95%) of healthy euthyroid subjects have a serum TSH concentration between 0.4 and 2.5 mIU/L, mean being 1.5 mIU/L (NACB, 2002; AACE, 2003).

The NAS report uses the old TSH reference upper limit of 5.0 mU/L in its discussion and interpretation of the findings by Bachiinski et al. (1985), thereby misinterpreting the actual findings.

The report states on Page 194:
[ http://darwin.nap.edu/books/030910128X/html/194.html ]

Bachinskii et al. (1985) examined 47 healthy persons, 43 with hyperthyroidism, and 33 persons with hypothyroidism. Prolonged consumption of "high-fluoride" drinking water (2.3 mg/L, as opposed to "normal" concentrations of 1 mg/L), by healthy persons was associated with statistically significant changes in TSH concentrations (increased), T3 concentrations (decreased), and uptake of radioiodine (increased), although the mean values for TSH and T3 were still within normal ranges (see Appendix E, Table E-6). The mean value of TSH for the healthy group (4.3 +/- 0.6 milliunits/L; Table E-6) is high enough that one expects a few individuals to have been above the normal range (typically 0.5 - 5 milliunits/; Larsen et al. 2002).

If the NAS panel had understood this matter properly, and used correct TSH reference levels, it would have had to state something like this:

The normal TSH reference range in healthy euthyroid US subjects is 0.4 and 2.5 mIU/L, the mean being 1.5 mIU/L (Hollowell et al. 2002).

In the data by Bachiinski et al (1985), the mean TSH levels were elevated in the control population drinking water with 1 ppm fluoride (mean TSH 2.4 +/- 0.2 mIU/L), while it was even more elevated in subjects consuming water with 2.3 ppm fluoride (mean TSH 4.3 +/- 0.6 mIU/L), indicating that TSH levels rise with increasing fluoride ingestion.

RECOMMENDATIONS:

The findings that even 1 ppm of fluoride in water - the amount deemed "optimal" for caries prevention - may raise TSH levels significantly, should invite rigorous re-examination not only of the 4 ppm MCL set by the EPA, but also all public health programs designed to deliver fluoride to the population, including water fluoridation programs, school programs, etc. . The public should be warned to refrain from any high fluoride sources routinely consumed, including teas (black, green, iced, brick) and oral care products.

TSH levels above 2.5 mIU/L are indicative of mild thyroid failure (subclinical hypothyroidism). Mild thyroid failure has been associated with hypertension, elevated cholesterol and cardiac abnormalities, as well as depression, memory loss, cognitive impairment, peripheral nerve dysfunction, skeletal muscle abnormalities, and a variety of neuromuscular complaints. Mild thyroid failure in pregnant women may result in reduced intellectual development of their euthyroid offspring (McDermott & Ridgway, 2001; Ayala & Wartofsky, 2002).

The Whickham survey, a longitudinal study, indicated that patients with TSH levels greater than 2.0 mIU/L have an increased risk of developing overt hypothyroidism over the next 20 years (Vanderpump et al, 1995).

Andreas Schuld

REFERENCES:

American Association of Clinical Endocrinologists (AACE) - Summaries
of 3 Lectures Presented at the 12th Annual Meeting of the AACE in
San Diego, California on May 14, 2003, AACE NEWSLETTER - May 2003
http://www.thyroidtoday.com/TTLibrary/c ... letter.pdf

Ayala AR, Wartofsky L - "The case for more aggressive screening and treatment of mild thyroid failure" Cleve Clin J Med 69(4):313-20 (2002)

Hollowell JG, Staehling NW, Flanders WD, Hannon WH, Gunter EW, Spencer CA, Braverman LE - "Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III)" J Clin Endocrinol Metab.87(2):489-99 (2002)

McDermott MT, Ridgway EC - "Subclinical hypothyroidism is mild thyroid failure and should be treated" J Clin Endocrinol Metab 86(10):4585-90 (2001)

National Academy of Clinical Biochemistry, Laboratory Medicine Practice
Guidelines - Thyroid Disease (2002)

Vanderpump MP, Tunbridge WM, French JM, Appleton D, Bates D, Clark
F, Grimley Evans J, Hasan DM, Rodgers H, Tunbridge F - "The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey" Clin Endocrinol (Oxf). 43(1):55-68 (1995)
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