Context: The incidence of menstrual disorders declines during adolescence. The mechanism responsible is unknown.
Objective: The objective of the study was to test the hypothesis, formulated a priori, that the dependence of LH pulsatility and ovarian function on energy availability declines with gynecological age (years since menarche).
Design: The study was a controlled experiment repeated in two menstrual cycles, performed 2001-2004.
Setting: The study was conducted at a university laboratory and general clinical research center.
Participants: The study population consisted of healthy, habitually sedentary, young women of normal body composition with 5-8 yr (adolescents, n = 9) and 14-18 yr (adults, n = 10) of gynecological age recruited by advertisement from approximately 9000 women aged 18-34 yr in a college community. Samples were similar in age of menarche, length of menstrual cycle and luteal phase, body size and composition, aerobic capacity, and dietary intake. None were withdrawn due to adverse effects.
Interventions: Interventions included energy availabilities of 45 and 10 kcal/kg of fat-free mass per day for 5 d in the early follicular phases of separate menstrual cycles in random order.
Main outcome measures: LH pulsatility, estradiol, and luteal phase length were measured.
Results: Low energy availability reduced LH pulse frequency in adolescents (P < 0.01) but not adults (P = 0.39), did not increase LH pulse amplitude in either group (both P = 0.13), and suppressed 24-h mean LH in adolescents (P = 0.01) but not adults (P = 0.72). Estradiol was unaffected (both P = 0.48), but the subsequent luteal phase was shorter in adolescents (P < 0.01).
Conclusions: In women of normal body composition, the response of LH pulsatility and ovarian function to 5 d of low energy availability disappears by 14 yr of gynecological age.