Cold-induced vasodilation comparison between Bangladeshi and Japanese natives

BACKGROUND: The human thermoregulation system responds to changes in environmental temperature, so humans can self-adapt to a wide range of climates. People from tropical and temperate areas have different cold tolerance. This study compared the tolerance of Bangladeshi (tropical) and Japanese (temperate) people to local cold exposure on cold-induced vasodilation (CIVD). METHODS: Eight Bangladeshi males (now residing in Japan) and 14 Japanese males (residing in Japan) participated in this study. All are sedentary, regular university students. The Bangladeshi subject's duration of stay in Japan was 2.50 ± 2.52 years. The subject's left hand middle finger was immersed in 5 °C water for 20 min to assess their CIVD response (the experiment was conducted in an artificial climate chamber controlled at 25 °C with 50% RH). RESULTS: Compared with the Bangladeshi (BD) group, the Japanese (JP) group displayed some differences. There were significant differences between the BD and JP groups in temperature before immersion (TBI), which were 33.04 ± 1.98 and 34.62 ± 0.94 °C, and time of temperature rise (TTR), which were 5.35 ± 0.82 and 3.72 ± 0.68 min, respectively. There was also a significant difference in the time of sensation rise (TSR) of 8.69 ± 6.49 and 3.26 ± 0.97 min between the BD and JP groups, respectively (P < 0.05). Moreover, the JP group showed a quick TTR after finishing immersion. CONCLUSIONS: The Japanese group (temperate) has a higher tolerance to local cold exposure than the Bangladeshi group (tropical) evaluated by the CIVD test.