Day-time changes for pituitary-thyroid hormones denote a rhythmic structure not detectable in elderly subjects

Area of Science:

• Endocrinology
• Chronobiology
• Gerontology

Background:

• Thyroid hormones play a crucial role in regulating metabolism and physiological functions.
• Circadian rhythms influence hormone secretion patterns, impacting overall health.
• Age-related changes in endocrine function are common, but specific alterations in thyroid hormone rhythms require further investigation.

Purpose of the Study:

• To investigate and compare daytime concentrations of thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free T3 (FT3), and free T4 (FT4) in young and elderly healthy volunteers.
• To analyze the circadian patterns of these hormones using cosinor analysis, focusing on daytime variations.
• To identify potential age-related dyssynchronies in the pituitary-thyroid axis.

Main Methods:

• Blood samples were collected during daytime hours from clinically healthy young (20-27 years) and elderly (70-81 years) subjects.
• Cosinor analysis was employed to model the best-fitting sinusoidal wave representing the circadian rhythm over a 24-hour period.
• Validation of the reconstructed circadian waves was performed for all measured hormones in young subjects and for T4 in elderly subjects.

Main Results:

• Circadian sinusoidal waves were successfully reconstructed for TSH, T3, T4, FT3, and FT4 in young individuals.
• Elderly subjects showed evidence of dyssynchrony in the daytime patterns of TSH, T3, FT4, and FT3, which was not observed in the young group.
• The circadian rhythm of T4 in elderly individuals was validated with limitations.

Conclusions:

• Daytime thyroid hormone patterns in the elderly are characterized by dyschronism, unlike in younger adults.
• Investigating daytime hormone concentrations is a practical and cost-effective approach to understanding circadian rhythm disturbances in the pituitary-thyroid axis in aging populations.
• These findings highlight potential age-related alterations in thyroid hormone regulation that may impact health outcomes.