What you've heard
Eleven minutes of cold and fifty-seven minutes of heat a week is the optimal protocol
Verdict
Not a protocol
Is 11 minutes of cold and 57 of heat a week optimal?
Not a protocol.
Nobody tested it. The numbers come from a small Danish study comparing a handful of young men who swam in winter water and used a sauna with men who did not. Those figures were the swimmers' own weekly averages. They made more heat in the cold, but their brown fat responded no more strongly than the controls', and the authors warned that so small a sample could mislead in either direction. It is a description of what a few volunteers already did, measured once.18
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
- 18.Søberg, S., Löfgren, J., Philipsen, F.E., Jensen, M., et al. (2021). "Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men." Cell Reports Medicine, 2(10), 100408. https://doi.org/10.1016/j.xcrm.2021.100408 (8 swimmers and 8 controls, one swimmer excluded; the weekly means are self-reported by seven swimmers)
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.