Menstrual Disruption with Exercise Is Not Linked to an Energy Availability Threshold

Area of Science:

• Reproductive Endocrinology
• Sports Science
• Nutritional Physiology

Background:

• Chronic reductions in energy availability (EA) are known to suppress reproductive function.
• A specific calculation of EA considers dietary energy remaining after exercise for all physiological needs.
• Previous research indicated luteinizing hormone pulse frequency reductions when EA falls below 30 kcal·kg·fat-free mass (ffm)·d.

Purpose of the Study:

• To investigate if menstrual disturbances (MD) are induced when energy availability (EA) is below 30 kcal·kg ffm·d.
• To determine the relationship between quantified energy availability and the occurrence of menstrual disturbances.

Main Methods:

• Thirty-five sedentary, ovulatory women (age 18-24) underwent a 3-month diet and exercise intervention.
• Participants were randomized to varying negative energy balance groups.
• Menstrual disturbances were assessed using urinary hormone metabolites (estrone-1-glucuronide, pregnanediol glucuronide), luteinizing hormone, and menstrual cycle data.

Main Results:

• A 9% decrease in the likelihood of menstrual disturbances was observed for each unit increase in energy availability (EA) (OR, 0.91; P = 0.010).
• No specific EA threshold was identified below which menstrual disturbances were consistently induced.
• Hormone levels (estrone-1-glucuronide, pregnanediol glucuronide) and luteal phase length decreased significantly with lower EA tertiles.

Conclusions:

• Findings suggest that menstrual disturbances increase linearly with decreasing energy availability, rather than being triggered by a specific threshold.
• Monitoring energy availability may be a viable strategy for preventing menstrual disturbances.
• Further research can explore simplified metabolic assessments for tracking EA and reproductive health.