Body Temperature Regulation: Weight Is Not the Only Factor

The belief that overweight people always feel hot and thin people always feel cold is a myth. Thermal perception is multifactorial.

Key Determinants of Thermal Sensation

• Metabolic rate: Higher resting metabolic rate → more heat production → feeling warmer. Varies by thyroid status, muscle mass, genetics, age.
• Body composition: Adipose tissue insulates (reduces heat loss) but also produces less heat per kg than muscle. Net effect varies.
• Vascular tone: Sympathetic control of cutaneous vasoconstriction/dilation—major regulator of heat dissipation.
• Hormones: Thyroid hormone (thermogenesis), estrogen/progesterone (menstrual cycle, menopause), catecholamines.
• Autonomic function: Dysautonomia (POTS, diabetic neuropathy) → impaired thermoregulation.
• Acclimatization: Chronic heat/cold exposure shifts thresholds.
• Circadian rhythm: Core temp nadir ~4 AM, peak ~6 PM.
• Medications: Beta-blockers (↓ heat dissipation), anticholinergics (↓ sweating), stimulants (↑ metabolism).
• Psychological factors: Anxiety → vasoconstriction (cold hands); stress → hyperthermia.

Clinical Pearls

• Hypothyroidism → cold intolerance (↓ basal metabolic rate).
• Hyperthyroidism → heat intolerance.
• Menopausal hot flashes = thermoregulatory instability, not ambient temperature.
• Raynaud's phenomenon = exaggerated vasoconstriction to cold/stress.

Thermal comfort is individual; assess holistically, not by BMI alone.