Effects of time-of-day on the noradrenaline, adrenaline, cortisol and blood lipidome response to an ice bath.
Level 2 - randomized trial
Individual crossover intervention trial in humans
PubMed 39779795 · doi:10.1038/s41598-025-85304-8
What was done
Twelve healthy young adults (6 women, 6 men; mean age 26 ± 5 years, BMI 23 ± 2 kg/m²) participated in a crossover study comparing responses to a 5-minute ice bath (8–12 °C) completed in the morning versus the evening on separate days. Diet, meal timing, and physical activity were standardized for the 24 hours preceding each session. Venous blood was collected before the bath and at 5 and 30 minutes post-immersion to measure hormones (noradrenaline, adrenaline, cortisol) and plasma lipid profiles via liquid chromatography mass spectrometry shotgun lipidomics.
What was found
Plasma fatty acids increased significantly only after morning ice baths, rising from 5.1 ± 2.2% at baseline to 6.0 ± 2.4% at 5 minutes (P = 0.029) and 6.3 ± 3.1% at 30 minutes (P = 0.008). Noradrenaline increased similarly regardless of time of day: morning levels rose by 127 ± 2% (from 395 ± 158 to 896 ± 562 pg/ml, P = 0.025) and evening levels rose by 144 ± 2% (from 385 ± 146 to 937 ± 547 pg/ml, P = 0.015). Cortisol was higher overall in the morning than the evening across all timepoints (pre: 179 ± 108 vs 91 ± 59 pg/ml, P = 0.013; post 5 min: 222 ± 96 vs 101 ± 52 pg/ml, P = 0.001; post 30 min: 190 ± 96 vs 98 ± 54 pg/ml, P = 0.009). No sex differences were observed in hormonal or lipidome responses.
Why it matters
This study provides initial evidence that acute lipolytic responses to cold water immersion depend partly on circadian timing, with morning exposure inducing greater circulating fatty acid release despite comparable sympathetic activation.
Limits
The sample size is very small (n = 12), and the abstract does not report whether the crossover order was randomized. Measurements were limited to 30 minutes post-exposure, precluding evaluation of longer-term metabolic kinetics. Specific quantitative values for adrenaline were not reported in the abstract.
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