Cold Tolerance Variation: Individual and Population Differences

Cold tolerance is not uniform across individuals. Body composition, biological sex, age, physical fitness, and — to some extent — genetic ancestry all influence how a person responds to cold stress.

Key Determinants of Cold Tolerance

Factor	Effect on Cold Tolerance	Mechanism
Body fat	Insulation (reduces heat loss)	Subcutaneous fat: low thermal conductivity
Muscle mass	Shivering capacity	More muscle = more thermogenic potential
BAT activity	Non-shivering thermogenesis	More BAT = more efficient cold defense
Acclimatization	Enhanced thermogenesis, reduced cold shock	Weeks of cold exposure
Age	Reduced tolerance	↓ shivering, ↓ BAT, ↓ vasoconstriction with aging
Sex	Women: stronger peripheral vasoconstriction	Hormonal effects on alpha-adrenergic vascular tone

Sex Differences

Women and men respond differently to cold:

Where women are more tolerant:

• Core temperature is better preserved (less total heat loss per unit time in some studies)
• Higher body fat provides more insulation

Where women are less tolerant:

• Peripheral (hand/foot) temperatures drop more quickly
• Stronger vasoconstriction → colder extremities subjectively
• More likely to develop Raynaud’s phenomenon (3:1 female:male ratio)

Mäkinen (2010) documented that at equivalent cold air exposure, women’s finger and toe temperatures fell lower and faster than men’s — a consequence of stronger alpha-adrenergic vasoconstriction response, not worse core thermoregulation.

Population Adaptations

Inuit (Circumpolar populations):

• Elevated basal metabolic rate at rest — particularly notable in Arctic-adapted groups
• Higher plasma NE at thermoneutral — elevated sympathetic tone at baseline
• Some genetic variants (FADS gene cluster affecting fatty acid metabolism) may contribute to thermogenic efficiency

Korean/Japanese Haenyeo Divers:

• Classic demonstration of metabolic cold acclimatization from occupational cold exposure
• Hong (1963): BMR elevated 35% in winter vs summer; decreased after cessation of diving
• More recent studies show elevated BAT activity vs age-matched non-divers

Australian Aboriginal Cold Adaptation:

• Scholander (1958): Aboriginals sleeping in cold showed a distinct “hypothermic” pattern — allowed core temperature to fall further before shivering
• Interpreted as insulative + hypothermic acclimatization type

Body Composition Trade-offs

Body fat provides insulation (reducing heat loss) but obese individuals have:

• Lower BAT activity and mass
• Reduced sympathetic sensitivity of BAT
• Potentially impaired vasoconstriction efficiency

For cold water immersion specifically, more subcutaneous fat means slower core cooling (useful in prolonged exposure). For metabolic cold adaptation, obesity-related reduced BAT activity is a disadvantage.

Lean, muscular individuals have high shivering capacity but cool faster in water — they must compensate through acclimatization or rely heavily on shivering thermogenesis.