Johannes D. Veldhuis, MD


March 15, 2000

In This Article

Neuroendocrine Rhythms in Aging

Neuroendocrine rhythms are altered with aging. For example, although the role of melatonin in human aging is not known, the peak nighttime release of melatonin decreases by approximately 50% with aging. Other CNS timekeeping centers, such as the suprachiasmatic nuclei (SCN), show aging-dependent alterations, as reflected in changing 24-hour rhythms of GH, prolactin, cortisol, thyroid-stimulating hormone (TSH), GH, and LH. For example, over the age range of 18-80 years in humans, the secretion of cortisol, which is driven by ACTH, progressively exhibits an earlier maximum (phase advance), a higher late-day nadir, and a smaller variation in secretion over 24 hours.[10] In contrast, the 24-hour periodicity of cortisol secretion remains stable across the life span.[11] With aging, there is a blunting of the presleep peak of TSH. Levels of GH manifest a global (day and night) suppression of amplitude with aging.[10,12]

Neurophysiologic outcomes, such as circadian temperature rhythms, tend to show phase advance and amplitude suppression with aging. Extended daylong and inter-diem monitoring of cardiovascular indices may identify patients at higher risk for arrhythmia or myocardial infarction. Knowledge of circadian rhythms has resulted in the development of chronopharmacotherapy, or timed drug delivery based on the circadian cycle of the patient, in an effort to obviate drug toxicity and enhance medication efficacy.[13]