Pre-sleep milk-derived proteins do not impair sleep or recovery in elite female athletes.

BACKGROUND

Sleep is essential for athlete recovery and performance, yet athletes frequently experience restricted or poor-quality sleep. Pre-sleep feeding (PSF) has emerged as a strategy to support recovery, but randomized, double-blinded, crossover trials comparing PSF macronutrient options on objective and subjective sleep outcomes in elite female athletes remain limited.

METHODS

Twenty-five National Collegiate Athletic Association (NCAA) Division I female athletes (18-25 years old) were recruited; 21 completed the trial. In a randomized, double-blinded, placebo controlled, crossover design conducted over 4-8 weeks, participants consumed four treatments for three consecutive nights each: 40 g casein protein (CAS; 160 kcal), 40 g α-lactalbumin protein (ALA; 160 kcal), 40 g carbohydrate (CHO; 160 kcal), and 40g of a placebo (PLA; 5 kcal), with a minimum three-day washout between conditions. Supplements were consumed ~2 h after the final meal and ~30 min before bedtime as the last caloric intake of the day. Objective outcomes were obtained from the WHOOP 4.0 device (total sleep time (TST), sleep onset latency (SOL), sleep efficiency (SE), resting heart rate (RHR), and heart rate variability (HRV)). Subjective outcomes were assessed each morning via questionnaires (subjective sleep quality (SSQ), subjective sleep onset latency (SSOL), and subjective recovery (SREC)). Nocturnal interstitial glucose was assessed via blinded continuous glucose monitoring (CGM) in a subset (n = 6). Sleep and recovery variables were analyzed using one-way repeated-measures analysis of variance (ANOVA) to evaluate treatment effects across the four supplementation conditions. For CGM data, a two-way repeated-measures ANOVA was used to evaluate main effects of treatment and time, as well as the treatment × time interaction. Tukey's post hoc testing was used with significance set at p < 0.05.

RESULTS

No significant treatment effects were observed for TST, SOL, SE, RHR, or HRV (p > 0.05). TST ranged from 7.47-7.62 h, SE from 91.5-92.0%, RHR from 53.5-54.1 bpm, and HRV from 98.2-103.9 ms across conditions. No significant treatment effects were detected for SSQ, SSOL, or SREC (p > 0.05); SSQ ranged from 69-75%, SSOL from 16-20 min, and SREC from 61-66%. In the CGM sub-analysis, a main effect of time was observed for nocturnal glucose (p = 0.008), but no differences among treatments (p = 0.187) or a time × treatment interaction (p = 0.550) were detected.

CONCLUSIONS

In NCAA Division I female athletes, three consecutive nights of pre-sleep ingestion of CAS, ALA, or CHO did not impair objective or subjective measures of sleep or recovery compared with PLA. These findings demonstrate that pre-sleep feeding, regardless of macronutrient type, can be incorporated without negatively affecting sleep quality or recovery metrics.

TRIAL REGISTRATION: ClinicalTrials.gov (Identifier: STUDY00004409).