E-Newsletter No. 64

Adults with growth hormone deficiency (GHD) have lower lean body mass and greater mean body fat mass than age- and sex- matched controls.  Their exercise capacity is reduced, with average maximal oxygen consumption (VO2 max) values only 72%-82% of those predicted for age, sex,  and height. GH treatment improves this. Researchers led by George R. Merriam, M.D., of the VA and the University of Washington School of  Medicine in Seattle, compared the effect on aerobic exercise capacity of individualized GH dosing-the dosing strategy recommended in the  Society's Clinical Guideline on adult GHD-with fixed weight-based GH dosing, and sought to determine whether the increase in aerobic capacity  might itself be the result of increases in spontaneous physical activity during GH replacement therapy. Their results have been published in The Journal of Clinical Endocrinology & Metabolism. 

In a randomized, two-arm, parallel open-label study, the team gave GH replacement therapy to 29 adults with GHD due to hypothalamic-pituitary  disease. The 32-week therapy was either a fixed body weight-based dosing regimen (FD) or an individualized dose-titration regimen (ID). The  researchers assessed subjects for VO2 max and VO2 at the lactate threshold (LT) and ventilatory threshold (VT), using cycle ergometry. At the  start of the study, subjects also completed a questionnaire about their physical activity (weekly energy expenditure). 

In the group as a whole and within the ill group, VO2 max increased significantly from baseline to study end. During the treatment period, neither the  ID nor the FD group had significant changes in VO2 at LT, VO2 at VT, or in weekly energy expenditure. In both groups, lean body mass increased  significantly, with no difference between treatment modes.  

The scientists conclude that these results are clinically important because "they demonstrate that the lower GH doses achieved with individualized  dosing regimens now recommended by consensus clinical guidelines will improve aerobic exercise capacity." 

Hartman ML, Weltman A, Zagar N A, Qualy RL, Hoffman AR, Merriam GR 
Growth hormone replacement therapy in adults with growth hormone deficiency improves maximal oxygen consumption (VO2 max) independently of dosing regimen or physical activity.
(J Clin Endocrinol Metab Number 93: 125-130, 2008)

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