Endocrine Abstracts (2019) 65 OP5.1 | DOI: 10.1530/endoabs.65.OP5.1

Hypothalamic-pituitary-gonadal (HPG) axis suppression during basic military training in women despite increased adiposity and insulin resistance

Robert M Gifford1,2, Thomas J O'Leary3, Sophie L Wardle3, Julie P Greeves3, Richard A Anderson4, David R Woods2,5 & Rebecca M Reynolds1

1University/British Heart Foundation Centre for Cardiovascular Science, Edinburgh, UK; 2Research & Clinical Innovation, Royal Centre for Defence Medicine, Lichfield, UK; 3Department of Army Health and Physical Performance Research, Andover, UK; 4MRC Centre for Reproductive Health, Edinburgh, UK; 5Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, UK

Background: Low energy availability (LEA) in female athletes can result in HPG axis suppression. Basic military training (BMT) is physically arduous and associated with amenorrhoea and low-trauma fractures. We hypothesised that women undergoing BMT would demonstrate evidence of LEA and suppressed HPG function.

Design: Prospective study of 61 women undertaking 11-month BMT. Subjects acted as their own controls at baseline (all measures). Body composition measurement (DXA) was repeated after 3, 7 and 11 months; fasting blood (glucose, insulin (for homeostatic model of insulin resistance, HOMA2), leptin, inhibin B, estradiol, anti-Müllerian hormone (AMH), and FSH) after 7 and 11 months, and dynamic 1-h 10 µg GnRH test measuring LH and FSH after 7 months. Menstruation and ovulation were assessed in non-contraceptive pill-users (n=22) using diaries and weekly urinary progesterone : creatinine ratio, respectively.

Results: 52 women, aged 24.0±0.3 years, completed the study. Fat mass decreased 0.8 kg from baseline to month 3, increased 1.8 kg to month 7 and reverted to baseline by month 11 (P<0.001). Fat-free mass did not change (P=0.13). HOMA2 and leptin increased (both P<0.001), as did estradiol and inhibin B (P<0.05) while AMH was unchanged (P=0.6) (Table). Maximum and area-under-the-curve fold-responses of LH and FSH to GnRH were suppressed after 7 months (both P<0.001). Findings were unaffected by contraceptive use (effect × time P=0.8). Seven participants (32%) became oligo/amenorrhoeic. 87% of regular (23–35d) cycles were anovulatory.

Baseline7 months11 months
Leptin, ng.ml−18.09±3.1111.37±4.10*12.52±4.12*
Inhibin B, pg.ml−126.8±10.954.0±30.8*42.3±27.6*
Estradiol, pmol.l−183±46145±73*95±64
AMH, pmol.l−124.1±18.622.5±14.322.4±14.8

Conclusion: Evidence of adiposity-related adaptation suggests non-LEA stressors contributed to HPG axis suppression and follicular dysgenesis. Further studies are required to deliniate causes of reproductive dysfunction and associated pathology in military women.

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