Ab. Loucks et Em. Heath, INDUCTION OF LOW-T-3 SYNDROME IN EXERCISING WOMEN OCCURS AT A THRESHOLD OF ENERGY AVAILABILITY, The American journal of physiology, 266(3), 1994, pp. 180000817-180000823
To investigate the relationship between energy availability (dietary e
nergy intake minus energy expended during exercise) and thyroid metabo
lism, we studied 27 untrained, regularly menstruating women who perfor
med similar to 30 kcal.kg lean body mass (LBM)(-1).day(-1) of supervis
ed ergometer exercise at 70% of aerobic capacity for 4 days in the ear
ly follicular phase. A clinical dietary product was used to set energy
availability in four groups (10.8, 19.0, 25.0, 40.4 kcal.kg LBM(-1).d
ay(-1)). For 9 days beginning 3 days before treatments, blood was samp
led once daily at 8 A.M. Initially, thyroxine (T-4) and free T-4 (fT(4
)), 3,5,3'-triiodothyronine (T-3) and free T-3 (fT(3)), and reverse T-
3 (rT(3)) were in the normal range for all subjects. Repeated-measures
one-way analysis of variance followed by one-sided, two-sample post h
oc Fischer's least significant difference tests of changes by treatmen
t day 4 revealed that reductions in Tg (16%, P < 0.00001) and fT(3) (9
%, P < 0.01) occurred abruptly between 19.0 and 25.0 kcal.kg LBM(-1).d
ay(-1) and that increases in fT(4) (11%, P < 0.05) and rT(3) (22%, P <
0.01) occurred abruptly between 10.8 and 19.0 kcal.kg LBM(-1).day(-1)
Changes in T-4 could not be distinguished. If energy deficiency suppr
esses reproductive as well as thyroid function, athletic amenorrhea mi
ght be prevented or reversed by increasing energy availability through
dietary reform to 25 kcal.kg LBM(-1).day(-1), without moderating the
exercise regimen.