What you've heard
Cold water raises dopamine by 250%
Verdict
A real number, misapplied
A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose.
Does cold water raise dopamine by 250%?
A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose.
The figure comes from a laboratory study of young men who sat neck-deep in water at 57°F for a full hour, and the dopamine measured in their blood rose by the quoted amount. Blood dopamine is not brain dopamine, the study measured nothing about mood or motivation, and an hour at that temperature bears no resemblance to a two-minute plunge.14 The pooled trials of cold-water immersion found no effect on mood.
Where the book tests it
What the book recommends instead
Let your home move a little: cooler rooms in winter, and a bedroom that cools at night
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.How: in winter, set the thermostat around 64 to 66°F and add a sweater rather than a degree; turn the heat down at bedtime so the bedroom cools overnight (Chapter 8 covers sleep). Why: a few weeks of mild cold grew brown fat and improved insulin sensitivity in tiny trials. Safety: the World Health Organization treats 64°F as a safe indoor floor in cold seasons, and older people, infants and anyone with heart or lung disease may need it warmer.
End your shower with thirty seconds of cold, if you like it and your heart is healthy
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.for fewer sick daysEmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.for anything elseHow: finish a normal warm shower with thirty seconds of cold; longer did no better. Breathe slowly through the first gasp. Why: in the one large trial, it cut sickness absence by about three in ten, though not illness itself. Safety: with heart disease or an irregular heartbeat, ask a clinician first.
Heat: a sauna or a hot bath, a few times a week, if you have access and enjoy it
EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.How: about a quarter of an hour in a sauna, or a hot bath around 104°F for ten minutes or so. Taken an hour or two before bed, a warm bath or shower shortened the time people took to fall asleep in pooled studies (Chapter 8). Why: two large cohorts link regular heat with fewer heart deaths (that link is ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.; the frequency is untested), and small trials show better artery function in unfit people. Safety: no alcohol, drink water, rise slowly, and see "Safety" below.
Sources
- 14.Srámek, P., Simecková, M., Janský, L., Savlíková, J., and Vybíral, S. (2000). "Human physiological responses to immersion into water of different temperatures." European Journal of Applied Physiology, 81(5), 436-442. https://doi.org/10.1007/s004210050065 (one hour of head-out immersion at 14°C; metabolic rate rose about 350% and plasma dopamine 250%; mood was not measured)
Note numbers are those of Chapter 9, Heat and Cold.
This verdict is one of the "What you've heard" boxes in Chapter 9, Heat and Cold, where the book tests the claims people repeat against the studies behind them.
Educational content, not medical advice. Disclaimer.