Total and free triiodothyronine and thyroid-binding globulin concentration in elderly human persons

Area of Science:

• Gerontology
• Endocrinology
• Thyroid Research

Background:

• Healthy elderly subjects exhibit lower total thyroxine (TT4) and triiodothyronine (TT3) levels, with a more pronounced decrease in TT3.
• Thyroid hormone regulation and metabolism may change with aging, impacting overall health and requiring further investigation.

Purpose of the Study:

• To investigate the significance of altered thyroid hormone levels in healthy elderly individuals.
• To examine the relationship between free triiodothyronine (FT3), thyroid-binding globulin (TBG), and thyroid-stimulating hormone (TSH) in the elderly population.

Main Methods:

• Radioimmunoassay was used to measure FT3, TBG, and basal TSH in 22 healthy elderly subjects.
• Liver enzymes, cholesterol, and total protein concentrations were also analyzed.
• Comparison with a middle-aged group was performed for TBG levels.

Main Results:

• TBG levels were significantly increased in the elderly compared to the middle-aged group, with no correlation to TT4, TT3, or TSH.
• Basal TSH was detectable in all elderly subjects, unlike in 40% of younger subjects.
• Directly measured FT3 levels showed no correlation with calculated FT3 and could categorize elderly subjects into three distinct groups.

Conclusions:

• There is no direct correlation between TT4, TT3, elevated TBG, and FT3 in the elderly.
• Basal TSH may indicate potential hypothyroidism in the elderly, correlating with elevated cholesterol.
• Directly measured FT3 levels may subdivide thyroid hormone metabolism states in the elderly, possibly related to intracellular T4 concentration.