title: Relationship between age, percentage body fat, fitness, and 24-hour growth hormone release in healthy young adults: effects of gender.
abstract: We investigated whether gender affects the physiological relationships between the release of GH and age, body composition, and levels of physical fitness in humans. We studied 32 eumenorrheic females (age = 31 +/- 5 yr) and 12 males (age = 27 +/- 5 yr). Significant gender differences were found for peak oxygen consumption [VO2 peak = 40.5 +/- 6.9 (females) vs. 50.1 +/- 11.6 (males) ml/kg.min-1, P < 0.05] and body composition [hydrostatic weighing, percentage body fat = 28.7 +/- 5.4 (females) vs. 18.1 +/- 9.8 (males), P < 0.05] but not for body mass index [BMI = 23.7 +/- 3.1 (females) vs. 24.0 +/- 3.3 (males)]. Blood samples were drawn every 10 min for 24 h from 0800 h to determine integrated serum GH concentration [2350 +/- 1260 (females) vs. 3110 +/- 1760 (males) microgram/L x min]; females were studied during the early follicular phase (days 4-5) of the menstrual cycle. In females, a significant relationship existed between 24-h integrated serum GH concentration and age (r = -0.35, P = 0.05) but not BMI (r = -0.19, P = 0.29); the relationship between 24-h integrated serum GH concentration and VO2 peak (r = 0.31, P = 0.08) and percentage body fat (r = 0.29, P = 0.11) approached significance. In males, significant relationships existed between 24-h integrated serum GH concentration and age (r = -0.79, P = 0.002), percentage body fat (r = -0.75, P = 0.005), and VO2 peak (r = 0.58, P = 0.05) but not between 24-h integrated serum GH concentration and BMI (r = -0.53, P = 0.08). Standardized regression coefficients revealed that for each SD change in age, BMI, percentage body fat, or VO2 peak the associated change in 24-h integrated serum GH concentration was 1.9-2.6 times greater in males than in females. We conclude that age, percentage body fat (but not BMI), and fitness are related to 24-h GH release in young adults and that these relationships are considerably stronger in males than females.
authors.affiliation: Exercise Physiology Laboratory, Curry School of Education, University of Virginia, Charlottesville 22903.
authors.forename: A
authors.initials: A
authors.lastname: Weltman
authors.forename: J Y
authors.initials: JY
authors.lastname: Weltman
authors.forename: M L
authors.initials: ML
authors.lastname: Hartman
authors.forename: R D
authors.initials: RD
authors.lastname: Abbott
authors.forename: A D
authors.initials: AD
authors.lastname: Rogol
authors.forename: W S
authors.initials: WS
authors.lastname: Evans
authors.forename: J D
authors.initials: JD
authors.lastname: Veldhuis
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D000375:Aging / Q000378:metabolism*; D001823:Body Composition; D015992:Body Mass Index; D002940:Circadian Rhythm; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006801:Humans; D008297:Male; D010809:Physical Fitness; D012016:Reference Values; D012727:Sex Characteristics
chemical_list: D013006:Growth Hormone