Brown adipose fat (BAT) and thermography: the best time to expose yourself to the cold.
Cold exposure stimulates brown adipose fat, which could help improve cardiometabolic health.
But to optimize its benefits, knowing the best time to carry out exposure to the cold is necessary. For this reason, the researchers from Straat EM et al. 2022 have wanted to know the best time and if there are differences between the sexes and how brown adipose fat react.
The study of metabolism is one of the most developed areas in the application of thermography to health. There are numerous investigations about physiological processes such as the circadian rhythm, the relationship with the BMI, and even how food affects thermoregulation.
In this case, the authors (Straat EM et al 2022) wanted to relate the temperature of the supraclavicular area (Figure 1), closely related to the activity of brown fat (BAT), with the response to exposure to cold at different times.
Figure 1. Study on the relationship between supraclavicular area temperature and brown fat
(BAT)
Methodology of the study on cold activation of brown fat.
Twenty-four adults were selected into randomized groups: 12 men (18-31 years old; BMI 18-26 kg/m2) and 12 women (18-29 years old; BMI 18-26 kg/m2). They were subjected to a cooling protocol using water at two times of the day: in the morning (from 7:45 a.m.) and at night (from 7:45 p.m.), all went through both times in random order and with one day between these study days.
The water temperature was gradually lowered until the participants shivered or reached a temperature of 9°C. From that moment, the participants were exposed for another 90 minutes. (Figure 2)
Figure 2. Study design adapted from Straat ME, et al. J Clin Endocrinol Metab. 2022
Using indirect calorimetry, the researchers measured energy expenditure at four different times: initially under thermoneutral conditions (at 32°C when the body does not need to produce additional heat to maintain its core temperature), during the cooling phase, during the stable phase, and at the end of cooling (after 90 minutes). In addition, the temperature of the supraclavicular region was measured with thermography.
Study results.
The results showed that there are differences between men and women. While in men, the calorimetry data reported energy expenditure, and the temperature rose in the morning to a greater extent than when the protocol was done at night. In women, there were no differences between the caloric expenditure induced by the cold or in the temperature between the moments of the study. (Figure 3)
(Figura 3)
Figure 3. Study results from Straat ME, et al. J Clin Endocrinol Metab. 2022
In addition, the women were more tolerant of cold in the morning than at night, and their circulating free fatty acid concentrations, triglycerides, and cholesterol levels were higher after cold exposure in the morning than at night.
Study conclusions.
Morning cold exposure may improve metabolism and burn fat more effectively than evening cold exposure in men, but perhaps not in women.
Furthermore, the authors note that this could help to understand how certain regulatory processes such as those involving brown fat could also have their circadian rhythms (Straat ME et al. 2021). This could make biological sense because heat production from food digestion and activity decreases overnight, and body temperature needs to rise in the morning.
References.
Straat ME, Hogenboom R, Boon MR, Rensen PCN, Kooijman S. Circadian control of brown adipose tissue. Biochim Biophys Acta Mol Cell Biol Lipids. 2021 Aug;1866(8):158961. doi: 10.1016/j.bbalip.2021.158961. Epub 2021 Apr 30. PMID: 33933649.
ThermoHuman has had the support of the Funds of the European Union and the Community of Madrid through the Operational Programme on Youth Employment. Likewise, ThermoHuman within the framework of the Export Initiation Program of ICEX NEXT, had the support of ICEX and the co-financing of the European Regional Development Fund (ERDF). 
