The acclimatization of Haenyeo to a cold environment and occupational characteristics evaluated by orexin and irisin levels

Abstract

Background: Haenyeo is a woman who has the job of collecting seafood in the Jeju Sea at an average temperature of 13°C-14°C. The purpose of this study was to examine the cold acclimatization and occupational characteristics of Haenyeo through biomarkers such as orexin and irisin related to heat generation in the body.

Methods: Twenty-one Haenyeo and 25 people with similar age, body type, and body mass index were selected as the control group (Control G). In the cold exposure experiment, a climate chamber was set to 5°C and both feet were immersed in a 15°C water tank for 30 minutes. Tympanic temperature (T_ty) and skin temperature (T_sk) were measured, and the mean body temperature (mT_b) was calculated. Blood samples were collected before and immediately after the examination. Orexin and irisin levels were analyzed.

Results: Orexin levels were elevated after cold stimulation from 12.17 ± 4.44 to 12.95 ± 4.53 ng/mL (Haenyeo group [Haenyeo G], p < 0.01) and 10.37 ± 3.84 to 11.25 ± 4.02 ng/mL (Control G, p < 0.001). Irisin levels were elevated after cold stimulation from 4.83 ± 2.28 to 5.36 ± 2.23 ng/mL (Haenyeo G, p < 0.001) and 3.73 ± 1.59 to 4.18 ± 2.04 ng/mL (Control G, p < 0.001). The difference between Haenyeo G and Control G values in orexin and irisin appears not only in pre-exposure but also in post-exposure (p < 0.05).

Conclusions: Our experimental results suggest that Haenyeo G were relatively superior in cold tolerance to Control G under cold exposure conditions. Haenyeo's cold acclimatization is due to the basic differences in pyrogens regarding body temperature control such as orexin and irisin. This means that Haenyeo are advantageous for cold survival.

Keywords: Cold acclimatization; Elderly women diver; Haenyeo; Irisin; Orexin; Pyrogen.

Fig. 1. Orexin as a master switch of the orchestrated sympathetic response and thermoregulation by irisin. The sympathetic nervous system can activate the hypothalamus defense area to release orexin, and skeletal muscle to initiate the irisin response. Orexin is thought to be involved in the sympathetic pathway.

HR: heart rate; BMR: basal metabolic rate; VO₂: oxygen consumption; BP: blood pressure.

Fig. 2. TSK7+1 (Songkitopia, accuracy: ±0.1°C; Technox, Inc., Incheon, Korea). TSK7+1 is a precision thermistor that can be attached to the human body (head, chest, arm, hand, thigh, leg, and foot), and it meets ISO 9886 standards, enabling 8-channel temperature measurement and simultaneous monitoring.

Fig. 3. T_ty (Haenyeo G vs. Control G). Comparison of T_ty temperature before (pre) and after (post) cold stimulation (5°C ± 0.5°C). Values (Haenyeo G, n = 21 vs. Control G, n = 25) are presented as mean values ± standard deviation.

T_ty: tympanic temperature; Haenyeo G: Haenyeo group; Control G: control group. ^***p < 0.001, statistically significant difference between pre- and post-exposure values for Haenyeo G and Control G, respectively; calculated by paired t-test. ^##p < 0.01, statistically difference between Haenyeo G and Control G values in post-exposure; calculated by independent t-test.

Fig. 4. mT_b (Haenyeo G vs. Control G). Comparison of mT_b before (pre) and after (post) cold stimulation (5°C ± 0.5°C). Values (Haenyeo G, n = 21 vs. Control G, n = 25) are presented as mean values ± standard deviation.

mT_b: mean body temperature; Haenyeo G: Haenyeo group; Control G: control group. ^***p < 0.001, statistically significant difference between pre- and post-exposure values for Haenyeo G and Control G, respectively; calculated by paired t-test. ^##p < 0.01, statistically significant difference between Haenyeo G and Control G values in post-exposure; calculated by independent t-test.

Fig. 5. Orexin levels (Haenyeo G vs. Control G). Comparison of serum orexin levels before (pre) and after (post) cold stimulation (5°C ± 0.5°C). Values (Haenyeo G, n = 21 vs. Control G, n = 25) are presented as mean values ± standard deviation.

Haenyeo G: Haenyeo group; Control G: control group. ^**p < 0.01, statistically significant difference between pre- and post-exposure values in Haenyeo G; calculated by paired t-test. ^***p < 0.001, statistically significant difference between pre- and post-exposure values in Control G; calculated by paired t-test. ^#p < 0.05, statistical differences in Haenyeo G and Control G values in pre-exposure, as well as post-exposure; calculated by independent t-test.

Fig. 6. Irisin levels (Haenyeo G vs. Control G). Comparison of serum irisin levels before (pre) and after (post) cold stimulation (5°C ± 0.5°C). Values (Haenyeo G, n = 21 vs. Control G, n = 25) are presented as mean values ± standard deviation.

Haenyeo G: Haenyeo group; Control G: control group. ^***p < 0.001, statistically significant differences between pre- and post-exposure values for Haenyeo G and Control G, respectively; calculated by paired t-test. ^#p < 0.05, statistical differences in Haenyeo G and Control G values in pre-exposure, as well as post-exposure; calculated by independent t-test.