Table 1.

Cold habituation in indigenous populations.

	Study Sample	Habituation Length	Habituation Temperature	Cold Testing Procedure	Results/Findings
Brown [57]	22 M Eskimos	Lifetime	Seasonal Variation; outdoor temp 0–19°C, indoor temp 20°C at time of collection	Room air at 20°C, Hand/Forearm Immersion in 5–45°C water-bath	↑ hand blood flow (11–313%), ↓rate of reduction of hand blood flow in Eskimo vs. white control at water-bath temperatures between 5–42.5°C
Brown [59]	29 M Eskimos	Lifetime	Seasonal Variation; indoor temp 20°C (RH 50–60%) at time of collection	Room air at 20°C (bared and clothed forearm), Hand/Forearm Immersion in 5–45°C water-bath	↑ clothed forearm blood flow at any given water bath temperature <45°C vs. white control; ↑ forearm blood flow and ↓ muscle temperature in Eskimo during the 2nd hr of 10–38°C water bath; with 5°C ↓ muscle temperature was faster and larger
Scholander [63]	6 M Australian Aborigines	Lifetime (clothed during the day and nude overnight)	Air temperature in the region typically drops as low as 0°C in the early mornings	Natural night time exposure and observation (naked with fire and naked without fire)	In light sleeping bags without fire, ↓Tsk at the foot to 12–15°C in natives; natives slept soundly with unchanged resting heat production; white controls ↓ Tsk similarly but ↑ shivering and metabolism
Hammel [64]	8 M Central Aborigines; 7 M Control Whites; 9 M Tropical Aborigines	Lifetime (Aborigines clothed during the day and nude overnight)	Air temperatures at night dropped to 0–5°C	Natural night time exposure and observation in the winter, simulated cold night exposure in the summer using refrigerated meat van	Metabolism of central natives ↓ continually throughout the night with a Q10 of ~2 in summer as in winter, body temperature ↓ at a greater rate vs. whites; the metabolic rate adjustments to cold of the average tropical native fell between that of the control whites and the central natives
Andersen [60]	14 M Lapps	Lifetime	Seasonal Variation	Night time exposure to 0°C; in wind proof blanket sleeping bag on wire mesh sheet with extra woolen blankets and reindeer skins, last 2 layers removed after first 2 hrs	↑ shivering threshold compared to controls, ↓ metabolic heat production, ↓ Tc, ↑Tsk
Miller [58]	8 M, 3 F, 8 boy, 4 girl Eskimos	Lifetime	Seasonal Variation; between −20–5°C at time of collection	Cold air exposure (−6.6 to −7.2°C for men for 45 min, −2.6 to −4.8°C for women for 35 min and children for 30 min); wore parkas to ensure thermal comfort but no gloves	Adult male Eskimos ↑ hand and finger temperatures compared to white men; Eskimo children maintained finger temperatures at a nearly identical level as unacclimated white men despite ↓ hand volume; ↓ cold-induced pain with Eskimos; White males exposed to the cold regularly exhibited hand and finger temperature nearer to that of the Eskimos with considerable individual variability
Little [61]	41 Nunoa, Peru natives; 10 Mollendo, Peru natives; 8 whites	Lifetime	Nunoa and Mollendo natives share similar culture and ancestry but Mollendo is warmer throughout the year (10 to 19°C vs. −5 to 8°C)	Local exposure of the hand or foot to 0°C air for 60 minutes in the morning and afternoon; During foot cooling, Peruvians were tested at altitude (4000 m) while the whites were tested at ~ sea level	More rapid ↓ in toe and foot Tsk among white subjects during the first 30 min of foot cold exposure; with hand cooling, finger Tsk showed a steeper ↓ amongst whites that began to level off at the 40th minute of cold exposure; Peruvians showed CIVD cycling at much ↑ temperatures than whites but with low amplitude during foot cold air exposure; ↔ between Nunoa and Mollendo Peruvians