Table 4

Hormonal and metabolic parameters across 4 months of acclimation

Month 1: 24°CMonth 2: 19°CMonth 3: 24°CMonth 4: 27°CPtrend
24°C19°C24°C19°C24°C19°C24°C19°C24°C19°C
Sympathoadrenal
 Urinary epinephrine (μg/day)7.5 ± 5.08.0 ± 4.87.5 ± 3.98.3 ± 5.67.5 ± 4.47.7 ± 4.68.3 ± 6.17.7 ± 5.10.970.94
 Urinary norepinephrine (μg/day)46 ± 2953 ± 1456 ± 3064 ± 2035 ± 961 ± 18a37 ± 558 ± 240.420.56
Glucocorticoid axis
 ACTH AUC (pg ⋅ min/mL)207 ± 61199 ± 73199 ± 51197 ± 65203 ± 74176 ± 61209 ± 71199 ± 830.200.40
 Cortisol AUC (μg ⋅ min/mL)0.96 ± 0.140.91 ± 0.130.87 ± 0.100.95 ± 0.120.81 ± 0.130.84 ± 0.170.90 ± 0.150.88 ± 0.220.140.39
 Urinary cortisol (μg/day)49 ± 936 ± 1349 ± 2739 ± 939 ± 1138 ± 1139 ± 2249 ± 210.420.25
Thyroid axis
 TSH AUC (μIU ⋅ min/mL)7.8 ± 3.58.0 ± 2.87.5 ± 3.67.3 ± 2.18.6 ± 4.37.3 ± 2.28.8 ± 3.5c7.6 ± 1.90.380.39
 Free T4 AUC (pg ⋅ min/mL)95 ± 1395 ± 993 ± 1292 ± 1293 ± 993 ± 1190 ± 994 ± 90.390.54
 Free T3 AUC (pg ⋅ min/mL)26 ± 127 ± 129 ± 2b28 ± 128 ± 327 ± 226 ± 2d28 ± 20.160.59
 Free T3/free T4 AUC2,381 ± 4902,410 ± 3452,642 ± 574b2,556 ± 3932,513 ± 4492,511 ± 4662,515 ± 4812,491 ± 4030.060.41
Glucose and lipid metabolism
 Total glucose AUC (mg ⋅ min/mL)7.38 ± 0.647.32 ± 0.377.22 ± 0.517.25 ± 0.637.22 ± 0.737.32 ± 0.637.14 ± 0.517.11 ± 0.740.750.71
 Postprandial glucose AUC (mg ⋅ min/mL)2.73 ± 0.272.68 ± 0.342.59 ± 0.132.68 ± 0.292.64 ± 0.402.57 ± 0.292.64 ± 0.152.53 ± 0.270.790.63
 Total insulin AUC (IU ⋅ min/L)170 ± 102210 ± 83198 ± 97143 ± 49212 ± 118186 ± 123171 ± 87182 ± 1280.080.44
 Postprandial insulin AUC (IU ⋅ min/L)106 ± 64133 ± 57111 ± 5277 ± 22132 ± 85114 ± 80103 ± 55109 ± 790.190.31
 Total free fatty acid AUC (mEq ⋅ min/L)3.53 ± 0.703.76 ± 1.053.36 ± 0.313.37 ± 1.162.73 ± 0.863.20 ± 0.403.65 ± 1.093.76 ± 0.410.360.68
 Fasting total cholesterol (mg/dL)120 ± 24132 ± 24117 ± 16136 ± 110.13
 Fasting LDL (mg/dL)71 ± 2175 ± 2162 ± 1376 ± 100.20
 Fasting TG (mg/dL)57 ± 1668 ± 2768 ± 1565 ± 220.31
 Fasting HDL (mg/dL)38 ± 744 ± 741 ± 746 ± 4d0.03
Adipokine
 Leptin AUC (ng ⋅ min/mL)16 ± 515 ± 614 ± 3b12 ± 2a,b29 ± 1526 ± 1125 ± 1225 ± 11c0.010.002
 Adiponectin AUC (pg ⋅ min/mL)99 ± 38103 ± 37117 ± 51b127 ± 49a,b78 ± 3177 ± 3274 ± 32c82 ± 38c0.00070.0003
 FGF21 AUC (pg ⋅ min/mL)333 ± 57411 ± 104343 ± 46460 ± 91a,b350 ± 25400 ± 80370 ± 37435 ± 750.280.10
  • Data are means ± SD. At the end of each testing month, subjects underwent acute thermometabolic evaluation at either 24°C or 19°C. ACTH, adrenocortotropic hormone.

  • aP < 0.05 compared with 24°C during acute thermometabolic evaluation each month;

  • bP < 0.05 (month 1 vs. 2),

  • cP < 0.05 (months 2 vs. 4), and

  • dP < 0.05 (months 1 vs. 4) compared with matching measurement at the same temperature performed at respective months as indicated.