Resting oxygen consumption and energy expenditure is sensitive to slight alterations
in thyroid function. This means that timing and magnitude of cold adaptation would
to some extent depend on thyroid function. Local thyroid hormone metabolism is important
for energy expenditure and dissipation of heat in special tissues. Recruitment of
brown adipocytes and upregulation of uncoupling protein 1 in mitochondria depends
on high tissue T3 concentrations. Most of this T3 is derived from local 5' deiodination of T4. Brown fat is vital for cold exposed mice and rats, and may be important for temperature
adaptation in human neonates. The role of thyroid hormone metabolism in adult human
cold adaptation has not been finally clarified. Hypothetically, cold exposure may
enhance T3 production by deiodination of T4 in skeletal muscle, which may enhance heat production in muscle via a change in muscle
fiber type. Another hypothetical possibility is recruitment of brown adipocytes embedded
in white adipose tissue in human adults. Understanding cold adaptation in human adults
may lead to development of new drugs against obesity.
Arctic residence - Brown adipose tissue - Cold adaptation - Obesity - Thyroid hormone
metabolism - Uncoupling protein
