The influence of age on endocrine responses to ultraendurance stress.

Background: Aging produces significant changes in the human endocrine system. This study was designed to determine if elderly and younger individuals differ in various endocrine measures before and after ultraendurance stress.

Methods: Sixteen young and 19 older subjects competing in a world championship triathlon had blood samples acquired for 13 hormones before, immediately after the event, and 18 hours into recovery.

Results: Following the triathlon, almost every hormone level increased. Significantly higher basal circulating levels of dihydroepiandrosterone sulfate (DHEA-S) and thyroid stimulating hormone (TSH) were found in 20-year-old individuals, whereas higher levels of norepinephrine (NEPI) and sex hormone binding globulin (SHBG) were found in the 50- to 74-year-old group. Older subjects had lower postexercise levels of EPI, DHEA-S, GH, and PRL and higher postexercise levels of estradiol than younger individuals. Similarity in pre- and postrace weights as well as Hgb and Hct levels suggested that dehydration, while present, did not significantly contribute to the endocrine changes.

Conclusions: Ultraendurance stress produced dramatic increases in all but one of the hormones evaluated. Whether frequent exercise can alter the endocrine changes that occur with aging cannot be answered by this study. It is clear, however, that when comparisons are made with young active individuals, frequent exercise does not eliminate the differences in basal concentrations of TSH, DHEA-S, SHBG, and NEPI or exercise-induced release of estradiol, GH, and PRL that occur with aging.