Thyroid function of Japanese elderly
S. Kato1, T. Kuwahara1,2, T. Tagami3 & S. Nishi1
Serum TSH is the most sensitive index of thyroid function in the absence of hypothalamicpituitary disease.
However, TSH reference limits are controversial, particularly the upper limit. District and age subpopulations have unique TSH distribution. We investigated characterization of thyroid hormones in Japanese elderly. 859 participants (mean age 74.3 years) over 60 years without known thyroid disease were surveyed.
Percentages of people whose TSH were over 5.0 mU/l were respectively 9.2, 18.7, and 30.1% in male and 11.2, 15.4, and 16.4% in women among 60s, 70s, and over 80 years. A progressive increase in prevalence of TSH above 5.0 mIU/l with age existed.
Of 744 participants who were assayed concentrations of free T4, 703 subjects were within limits of free T4. Additionally, TSH, free T4, and free T3 of 610 subjects were assayed at the same time. A progressive decrease was observed in the concentration of free T3 with age in both sex, and TSH mildly increased with age.
In elder people, especially over 80 year male, these tendencies were clearer. Conversion from T4 to T3 might be decreased in Japanese elderly.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.