CIRCULATING CONCENTRATIONS OF FREE THYROXINE ARE INDEPENDENTLY ASSOCIATED WITH THOSE OF COBALAMIN (VIT B12) IN ELDERLY EUTHYROID SUBJECTS

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 437-470-Non-neoplastic Thyroid Disorders
Basic/Clinical
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-459
Graziano Ceresini*1, Fulvio Lauretani2, Elisa Usberti3, Michela Marina3, Marcello Maggio3, Stefania Bandinelli4, Gianpaolo Ceda3 and Luigi Ferrucci5
1Univ of Parma, Parma, Italy, 2University-Hospital of Parma, 3University of Parma, Parma, Italy, 4Geriatric Unit, Azienda Sanitaria Firenze, Florence, Italy, 5NIA/NIH, Baltimore, MD
Introduction. It is well known that serum levels of cobalamin (Vit B12) may be low in hypothyroid patients, probably due to a common autoimmune linkage between hypothyroidism and a decreased absorption of Vit B12. It has been shown that Vit B12 may play a role in the iodination of tyrosine in the thyroid gland, but little is known on the impact of such phenomenon on circulating levels of thyroid hormones.  The aim of this study was to verify whether circulating Vit B12 is associated with thyroid hormones and thyroptropin (TSH) concentrations in normal euthyroid  subjects of advanced age who, more frequently than young individuals, may be affected by undernutrition.

Methods. We studied N. 795 euthyroid elderly subjects, ( 345 M, 450 F) who participated in the InCHIANTI Study, a population-based study of community-dwelling individuals, aged 75 ±7.3 (M ±SD) years. Euthyroidism was defined based on normal plasma TSH levels. Also, plasma free thyroxine (FT4) and  free triiodothyronine (FT3) as well as serum Vit B12 levels were measured.  All hormonal evaluations were performed by immunochemiluminescence.  Vit B12 levels were measured by Radioimmunoassay with normal reference range of 200 to 920 pmol/L . Logistic regression analysis was used to examine the  cross-sectional association between FT3, FT4,TSH and circulating levels of Vit B12 after adjusting for age, sex and multiple potential confounders such  as, selenium, interleukin-6, transaminase, BMI, smoke, chronic heart failure, calory intake.

Results. All hormonal levels were within the normal reference range. Plasma concentrations of FT3, FT4, and TSH were 4.23±0.45 pg mL, 1.45 ±0.29 ng/dL, and 1.53±0.84 mIU/L, respectively. Circulating concentrations of Vit B12 were 344.02 ±264.16 pmol/L. The regression analysis demonstrated that FT4 levels were significantly associated with Vit B12 levels both in the analysis adjusted for age and sex,  ( beta coefficient, 0.0000817795; SE,0.00003852; P=0.0341) and the fully adjusted analysis (beta coefficient, 0.0001169418; SE, 0.00004251; P=0.0061). Neither FT3 nor TSH levels were associated with Vit B12 levels. Of interest, the association between FT4 and Vit B12 was  significant even when subjects with Vit B12 levels below the reference range were removed from analyses.

Conclusions. In euthyroid elderly subjects, circulating Vit B12 is associated with FT4. This phenomenon might be related to a positive effect of Vit B12 on thyroid hormone synthesis.

Nothing to Disclose: GC, FL, EU, MM, MM, SB, GC, LF

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