Practice cold exposure (cold shower or ice bath for 1 to 5 minutes) to boost attention, energy, and stimulate metabolism, while avoiding active rewarming immediately before sleep.

noli's read

The effect of cold exposure on energy and alertness is well-documented: a clinical physiology study by Srámek et al. (2000) shows a rapid and massive rise in stimulating neurotransmitters (such as dopamine and norepinephrine) following immersion. However, a 2021 systematic review published in MDPI tempers the impact on attention by revealing that, despite a subjective feeling of alertness, actual cognitive performance may be temporarily slowed immediately after the thermal shock. Regarding metabolism, a 2022 meta-analysis published in Frontiers validates the activation of brown fat and an immediate increase in energy expenditure. However, presenting this as a major weight-loss tool is an exaggeration, as the total additional caloric impact remains modest on a daily basis. Finally, the idea of avoiding active rewarming before bedtime is relevant, as the reflexive internal rewarming response that follows cold exposure can delay the drop in body temperature necessary to drift naturally into sleep.

the sources

1. 1NIH Office of Dietary Supplements 2026
2. 2Manson JE et al. 2019
3. 3Bhatt DL et al. 2019
4. 4Khan SU, Lone AN, Khan MS, et al. 2021
5. 5Liao Y, Xie B, Zhang H, et al. 2019
6. 6hubermanprotocols.com (fan reference guide)