The potential role of irisin in the thermoregulatory responses to mild cold exposure in adults.
Level 2 - randomized trial
Randomized crossover trial
PubMed 27006247 · doi:10.1002/ajhb.22853
What was done
Twenty-two adults (9 men, 13 women; mean age 57.7 ± 10.07 years, BMI 27.8 ± 4.52 kg/m²) underwent 90-minute exposures to 20°C (mild cold) and 25°C (control) in a randomized crossover design. Measured outcomes included resting metabolic rate (RMR), forearm-to-fingertip skin temperature gradient (FFG), in-the-ear temperature (IET), blood pressure, heart rate, and fasting blood levels of irisin, glucose, and insulin.
What was found
Mild cold exposure significantly increased FFG (+3.8 ± 3.0°C, P < 0.001), systolic blood pressure (+8 ± 13 mm Hg, P = 0.015), and diastolic blood pressure (+4 ± 6 mm Hg, P = 0.005), while decreasing IET (-0.24 ± 0.29°C, P = 0.001). Overall changes in RMR (+190 ± 570 kJ/d, P = 0.135), irisin, glucose, and insulin did not differ significantly between temperatures (absolute blood concentrations were not reported). In sex-specific responses, men showed significant increases in systolic BP (+12 ± 16 mm Hg, P = 0.02) and diastolic BP (+6 ± 7 mm Hg, P = 0.02) with decreased heart rate (-4 ± 3 bpm, P = 0.002), approximately 50% higher thermogenic responses, and women had approximately 25% greater vasoconstriction. After adjusting for age, sex, insulin sensitivity, and body composition, fold changes in irisin were inversely correlated with the respiratory quotient (r = -0.54, P = 0.048).
Why it matters
This study indicates that mild acute cold exposure stimulates cardiovascular and vasoconstrictive responses without altering absolute circulating irisin concentrations, though relative irisin variations correlate with elevated lipid oxidation during non-shivering thermogenesis.
Limits
The study had a small sample size (n = 22) restricted to middle-aged/older overweight adults. The 20°C stimulus may have been too mild or short to reliably evoke changes in endocrine irisin secretion, and baseline or absolute biochemical concentrations were omitted from the abstract.
Cited by
- supports Mild cold stress naturally lowers the respiratory quotient (RQ), shifting substrate utilization toward fat oxidation.