Studies in whole-body hyperthermia show that heating a person's body to mimic a fever can drastically reduce or even eliminate symptoms of severe depression. The mechanism is thought to involve the stimulation of serotonin production in the brain, similar to the action of antidepressant medications.
A study across 12 countries revealed that the diversity of a person's social network is one of the best predictors of their core body temperature. Participating in varied groups (work, family, sports, volunteering) provides a physical buffer that helps protect against the cold.
Intentionally raising core body temperature through heat training triggers powerful physiological adaptations. Athletes experience increased aerobic capacity, more efficient sweating, and a lower resting core temperature. This makes heat training the new equivalent of altitude training for boosting performance.
Temperature regulation is metabolically expensive. To conserve energy in the cold, humans "outsource" thermoregulation by investing in social relationships. Strong bonds allow us to huddle and share warmth, making our social network a literal portfolio to protect against the high energy costs of the environment.
A major Finnish study found that men who used saunas most frequently had less than half the rate of fatal heart attacks and a third the rate of Alzheimer's compared to infrequent users. This effect, which strengthens the cardiovascular system, is considered more powerful than many medications.
Contrary to common perception focused on climate change-induced heatwaves, the global death toll from cold is overwhelmingly larger than from heat. This holds true even in hot climates like sub-Saharan Africa, revealing humanity's deep evolutionary vulnerability to cold after losing most of our body hair.