Figure 4.

Diurnal thermoregulation and circulating hormones in adult humans

A subset of the subjects included in the preceding experiments were invited for a subsequent experiment to study diurnal thermoregulation at a thermal comfort state (winter swimmers, n = 5; controls, n = 6). n represents the number of human individuals in each group and is consistent throughout the figure unless otherwise specifically stated.

(A) Experimental setup. Subjects entered and spent the night at the laboratory before the recordings started and were then followed for 24 h.

(B) Number of steps by the two groups.

(C) Systolic blood pressure.

(D) Diastolic blood pressure.

(E) Core temperature recorded by an ingested temperature pill. Means without SD are shown. Area under the curve between groups is shown to the right.

(F) Sternum temperature recorded by iButtons. Means without SD are shown. Area under the curve between groups is shown to the right.

(G) BAT temperature recorded by using iButtons placed over supraclavicular BAT as detected from the IRT images during cooling. Means without SD are shown. Area under the curve between groups is shown to the right.

(H) BAT temperature comparing the average during the day (1:01–2:01 p.m.), night_low (4:01–4:11 a.m.), and night_high (4:49–4:59 a.m.).

(I) Plasma cortisol over 24 h. Because of lack of samples, n for cortisol analysis was n = 3 winter swimmers and n = 3 control subjects.

(J) Plasma IL-6 over 24 h.

(K) Plasma leptin over 24 h.

(L) Plasma adiponectin over 24 h.

Differences between groups and treatments were assessed using two-way ANOVA or mixed models and subsequent post-tests. Differences in AUC was assessed with an unpaired t test. Data are presented as mean ± SD. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001. See also Figure S3.