Abstract
BACKGROUND: Sleep is vital for athletic recovery. It’s theorized that pre-sleep macronutrient intake may influence sleep architecture and physiological restoration. α-lactalbumin (ALA) has drawn particular interest due to its high tryptophan content. However, the impact of hormonal contraceptive (HC) use on these responses remains unclear. In this pilot study, it was investigated whether HC status modulates sleep and recovery outcomes following pre-sleep macronutrient supplementation in elite female athletes. METHODS: Twenty-one NCAA Division I female athletes (soccer, softball, tennis; 20.0 ± 1.4 yrs, 1.7 ± 0.1 m, 66.9 ± 11.9 kg) completed a randomized, double-blind, placebo-controlled, crossover trial over a period of 4–8 weeks. Participants consumed 40 g of either casein (CAS), α-lactalbumin (ALA), carbohydrate (CHO), or a non-caloric placebo (PLA) on three consecutive nights, two hours after their last meal and thirty minutes before bed. Screening included the Athlete-Specific Sleep Questionnaire (ASSQ), medical history review, dual-energy X-ray absorptiometry (DEXA) and a menstrual status questionnaire. Objective sleep (total sleep duration [TSD], sleep latency [SL], sleep efficiency [SE], & wake duration [WD]) and recovery metrics (resting heart rate [RHR] and heart rate variability [HRV]) were captured using WHOOP bands (Boston, MA), with data averaged over the three-night period. Participants were stratified by self-reported hormonal contraceptive use (n = 8 HC, n = 13 non-HC). No distinction was made between types or formulations of HC. RESULTS: No significant differences were observed between groups in TSD (HC: 7.5 ± 0.7 hours; non-HC: 7.53 ± 0.68 hours; p = 0.9519), SL (HC 1.9 ± 1.8 min; non-HC 2.8 ± 2.6 min; p = 0.079), SE (HC 91.6 ± 2.7%; non-HC 91.8 ± 2.3%; p = 0.778), or WD (HC 0.7 ± 0.2 hrs; non-HC 0.7 ± 0.2 hrs; p = 0.585) across supplement conditions. HRV was significantly lower in HC users than non-users (87.5 ± 16.9 ms vs. 109.2 ± 35.8 ms; p = 0.0007) across all conditions. RHR was significantly elevated in HC users (57.1 ± 3.9 bpm) compared to non-users (52.2 ± 6.3 bpm; p = 0.0013), with the most pronounced difference during CHO supplementation (HC: 57.1 ± 3.9 bpm; non-HC: 51.8 ± 7.2 bpm; p = 0.0413). CONCLUSION: Hormonal contraceptive use does not significantly alter how female athletes respond to pre-sleep macronutrients in terms of sleep responses. However, HC users exhibited a significant difference in RHR during CHO supplementation compared to non-users. Future research should explore menstrual phase-specific responses to confirm efficacy and elucidate on the underlying mechanisms.