Abstract
Metabolic rate has been used in thermophysiological models for predicting the thermal response of humans. However, only a few studies have investigated the association between an individual’s trait-like thermal sensitivity and resting energy expenditure (REE), which resulted in inconsistent results. This study aimed to explore the association between REE and perceived thermal sensitivity. The REE of healthy adults was measured using an indirect calorimeter, and perceived thermal intolerance and sensation in the body were evaluated using a self-administered questionnaire. In total, 1567 individuals were included in the analysis (women = 68.9%, age = 41.1 ± 13.2 years, body mass index = 23.3 ± 3.3 kg/m2, REE = 1532.1 ± 362.4 kcal/d). More women had high cold intolerance (31.8%) than men (12.7%), and more men had high heat intolerance (23.6%) than women (16.1%). In contrast, more women experienced both cold (53.8%) and heat (40.6%) sensations in the body than men (cold, 29.1%; heat, 27.9%). After adjusting for age, fat-free mass, and fat mass, lower cold intolerance, higher heat intolerance, and heat sensation were associated with increased REE only in men (cold intolerance, P for trend = .001; heat intolerance, P for trend = .037; heat sensation, P = .046), whereas cold sensation was associated with decreased REE only in women (P = .023). These findings suggest a link between the perceived thermal sensitivity and REE levels in healthy individuals.
Keywords: metabolism, resting energy expenditure, thermal intolerance, thermal sensation, thermal sensitivity
1. Introduction
The thermal sensitivity of an individual is affected by various physiological factors.[1] In thermophysiological models for the prediction of the thermal response of humans, physiological parameters, including height, weight, body fat percentage, metabolic rate, blood flow rate, sex, and body surface area, serve as model inputs to predict the thermal response of humans including thermal comfort, sensation, and preferences under different environmental conditions.[1,2] Among these, the metabolic rate represents the heat generated within the body and is considered a major determinant of thermal response.[3] The metabolic rate generally refers to resting energy expenditure (REE), which is the energy required for the conservation of basic bodily functions, such as respiration, circulation, and body temperature, that constitute the largest fraction of total energy expenditure.[4]
Although REE, as a source of endogenous heat production,[5] might affect an individual’s level of thermal sensitivity and has been widely utilized in thermophysiological models,[1,6,7] only a few studies have investigated the association between an individual’s trait-like thermal sensitivity and REE, which resulted in inconsistent results. One study reported that women complaining of unusual coldness had lower REE than women without it when the REE was normalized for body surface area.[8] Another study reported that individuals who answered that their hands, legs, and abdomen were generally cold had lower REE than those with warm body parts, but the differences were not significant after adjusting for age, sex, and body mass index.[9] Cold sensation in extremities and aversion to cold are representative symptoms of Flammer syndrome (also known as vasospastic syndrome or primary vascular dysregulation[10]), and reduced heat production has been hypothesized as one of its underlying pathophysiological mechanisms.[11] However, 1 study reported a different result that women with Flammer syndrome had higher REE after adjusting for fat-free mass (FFM) and body core temperature.[12] Hypersensitivity to cold or heat is also a prominent component of cold or heat syndrome,[13] respectively (which are types of syndrome differentiations according to traditional East Asian medicine); 2 studies reported a significant association between these syndromes and REE after adjusting for age, sex, and FFM.[14,15] The inconsistencies might be due to the differences in the study design, such as a detailed definition of thermal sensitivity, accompanying symptoms that were considered in some studies on syndromes, potential confounding factors considered in the analyses, and small sample sizes.
Thermal sensitivity can be assessed objectively by defining the thermoneutral zone, which refers to the range of ambient temperature without regulatory changes in metabolic heat production or evaporative heat loss, or measuring the cutaneous thermal threshold, which refers to the limit that participants respond to a stimulus once they feel a temperature change. However, it is practically difficult to define the thermoneutral zone or thermal threshold individually, especially when the sample size is large. Thus, a questionnaire-based assessment of perceived thermal sensitivity has been used in various studies[16–19] and it has been useful in predicting physiological responses to thermal exposure.[8,20]
In this study, we hypothesized that thermal sensitivity is associated with REE in healthy individuals and aimed to investigate the association independently of possible covariates including age, sex, and body composition. We evaluated the level of thermal intolerance and sensation in the body as distinct components of perceived thermal sensitivity and explored their association with REE in each sex after adjusting for age, FFM, and fat mass (FM), which can influence REE.
2. Methods
2.1. Data and study population
This study analyzed data from the Korea Medicine Examination (KME) study, which aimed to build a large data infrastructure based on Korean Medicine. The KME study included 14 clinical questionnaires and physical examinations using 20 medical devices based on a previous feasibility study.[21] This study was conducted at the following 5 sites: Naju Dongshin University Korean Medicine Hospital, Pusan National University Korean Medicine Hospital, Gachon University Gil Medical Center, Dongguk University Ilsan Oriental Hospital, and Dunsan Korean Medicine Hospital of Daejeon University.
All participants were adults aged ≥19 years and had no cognitive impairment. The exclusion criteria were as follows: participants’ inability to move by themselves and a current diagnosis of cardiovascular diseases (e.g., myocardial infarction, congestive heart failure, angina, and arrhythmia), cerebrovascular diseases (e.g., cerebral infarction and paralysis), malignant neoplasms (e.g., cancer), mental illnesses (e.g., depression and anxiety disorder), rheumatoid arthritis, and thyroid diseases (e.g., hyperthyroidism and hypothyroidism). Participants were recruited from July 2020 to April 2021.
For this study, adults aged ≥70 years were excluded to reduce the heterogeneity of the sample. Those who were taking medication for diabetes or high blood pressure were excluded to avoid possible confounding effects of those diseases and medications on REE or thermal sensitivity.[22–24] Additionally, those who had 2 strong values within each thermal sensitivity category (i.e., “both cold intolerance ≥4 and heat intolerance ≥4 within an individual” or “cold sensation ≥4 and heat sensation ≥4 within an individual”) were excluded. Because our preliminary analysis (not shown) suggested that cold and heat sensitivity had an opposite relationship to REE, we speculated that the association between thermal sensitivity and REE in the participants with both strong cold and heat sensitivity within each category might be unclear or the characteristics of the association might be different from others, and thus, they need to be excluded in the investigation for the general association of thermal sensitivity and REE and should be investigated separately in future studies. Exclusion of those individuals improved the results of our previous work that investigated the association between thermal sensitivity and metabolic syndrome.[25] Moreover, those with missing or evidently erroneous values in the variables used in the analyses were excluded.
2.2. Ethical approval
The study was conducted following the Declaration of Helsinki and approved by the Institutional Review Board from each of the 5 hospitals assessed (Institutional Review Board of the Dongshin University Naju Korean Medicine Hospital: NJ-IRB-003, Pusan National University Korean Medicine Hospital, Institutional Review Board: PNUKHIRB-2020005, Institutional Review Board of Gil Medical Center, Gachon University: GIRB-20-113, Institutional Review Board of Dongguk University Ilsan Hospital: DUIOH 2020-04-002, and Institutional Review Board of Daejeon Korean Medicine Hospital of Daejeon University: DJDSKH-20-BM-07). Informed consent was obtained from all participants involved in this study.
2.3. Data collection
2.3.1. Perceived thermal sensitivity
Participants were instructed to complete questionnaires about perceived thermal sensitivity within the past month. Perceived thermal sensitivity is divided into 2 categories (thermal intolerance and thermal sensation) and each category has 2 dimensions (thermal intolerance: cold intolerance, heat intolerance; thermal sensation: cold sensation, heat sensation) (Table 1). Cold or heat intolerance was measured by asking the following question: “Do you feel cold (or hot) easily?” Responses were collected on a 5-point Likert scale (1 = never, 2 = hardly ever, 3 = moderate, 4 = severe, and 5 = very severe). These responses were classified into 3 categories: low (never and hardly ever), middle (moderate), and high (severe and very severe).
Table 1.
Dimensions of perceived thermal sensitivity and questions used for evaluation.
| Category | Dimension of perceived thermal sensitivity | Question |
|---|---|---|
| Thermal intolerance | Cold intolerance | Do you feel cold easily? |
| Heat intolerance | Do you feel hot easily? | |
| Thermal sensation | Cold sensation | How often do you experience a cold sensation in your body, regardless of the temperature around you? |
| Heat sensation | How often do you experience a heat sensation in your body, regardless of the temperature around you? |
Cold or heat sensation was measured by asking the following question: “How often do you experience a cold sensation (or a heat sensation) in your body, regardless of the temperature around you?” Respondents answered the question on a 5-point Likert scale (1 = never, 2 = rarely, 3 = sometimes, 4 = often, and 5 = always). The answers were dichotomized: no cold (or heat) sensation (never) and cold (or heat) sensation (rarely, sometimes, often, and always).
2.3.2. Resting energy expenditure measurements
REE was measured using a Quark RMR indirect calorimeter with a breath-by-breath gas exchange analysis (COSMED, Rome, Italy). The clinical research coordinators at each site received standard training and conducted measurements according to the standard operating procedure. Participants were advised to fast for at least 4 hours and have a small meal before the fast, not to smoke or consume caffeine for at least 24 hours, and abstain from drinking alcohol for 3 days before the examination. They were also instructed to avoid physical exercises that could have caused breathlessness or sweating on the day of measurement. After participants rested for 15 minutes, REE was measured for 15 minutes using a face mask while participants were awake and sitting on a chair. To maintain the steady state of the participants, measurements began when the respiratory quotient was below 0.85, and the first 5 minutes of measurements were discarded. Oxygen consumption and carbon dioxide production were measured via breath-by-breath analysis.
2.3.3. Body composition measurements
FM and FFM were measured with a multifrequency bioelectrical impedance analysis using BWA 2.0 (InBody, Seoul, South Korea). In addition, body height, weight, and body mass index were measured using BSM 370 (InBody).
2.4. Statistical analyses
The Chi-squared test and t test were used to compare the prevalence or means of characteristics between the sexes. The estimated marginal mean was calculated to compare the differences between groups, and an analysis of covariance was performed, controlling for age, FFM, and FM. Post hoc test comparisons were performed using the Tukey honest significant difference test. The P value for trend was estimated using multiple linear regression after adjusting for covariates. The normality of the data was checked using the Shapiro–Wilk test. All statistical analyses were performed using R version 4.1.2 (R Foundation for Statistical Computing, Vienna, Austria).
3. Results
3.1. Characteristics of study participants
From a total of 2198 participants, 20 were excluded due to refusal to undergo physical examination. Subsequently, an additional 611 individuals were excluded from this study for the following reasons: age ≥70 years (n = 31), current medication use for diabetes or hypertension (n = 161), presence of 2 strong values within each thermal sensitivity category (n = 202), and missing or evidently erroneous data in the variables utilized in the analyses (n = 217). Consequently, a total of 1567 participants were included in the final analysis (Fig. 1).
Figure 1.
Flowchart for the selection of the study population.
The demographic, anthropometric, body composition, metabolic, and thermal sensitivity characteristics of the study participants are shown in Table 2. Among the participants, 31.1% (n = 488) and 68.9% (n = 1079) were men and women, respectively. All characteristics, except FM, showed statistical differences between the sexes. The prevalence of high cold intolerance was 12.7% for men and 31.8% for women, and the prevalence of high heat intolerance was 23.6% for men and 16.1% for women. The prevalence of those experiencing cold sensations was 29.1% for men and 53.8% for women, and the prevalence of those experiencing heat sensations was 27.9% for men and 40.6% for women.
Table 2.
Characteristics of study participants by sex (n = 1567).
| Variable | Total | Men | Women | P value* |
|---|---|---|---|---|
| n (%) | 1567 (100.0%) | 488 (31.1%) | 1079 (68.9%) | |
| Age, yr, mean ± SD | 41.1 ± 13.2 | 39.5 ± 13.8 | 41.8 ± 12.9 | .002 |
| Height, cm, mean ± SD | 164.2 ± 8.3 | 173.5 ± 5.8 | 160.1 ± 5.4 | <.001 |
| Weight, kg, mean ± SD | 63.3 ± 12.2 | 75.1 ± 10.5 | 57.9 ± 8.7 | <.001 |
| BMI, kg/m2, mean ± SD | 23.3 ± 3.3 | 24.8 ± 3.0 | 22.5 ± 3.2 | <.001 |
| FFM, kg, mean ± SD | 43.9 ± 9.7 | 56.1 ± 6.6 | 38.3 ± 4.3 | <.001 |
| FM, kg, mean ± SD | 19.4 ± 6.1 | 19.0 ± 6.3 | 19.6 ± 6.0 | .072 |
| REE, kcal/d, mean ± SD | 1532.1 ± 362.4 | 1891.2 ± 322.3 | 1369.7 ± 243.0 | <.001 |
| Cold intolerance, n (%) | <.001 | |||
| Low | 243 (15.5%) | 131 (26.8%) | 112 (10.4%) | |
| Medium | 919 (58.6%) | 295 (60.5%) | 624 (57.8%) | |
| High | 405 (25.8%) | 62 (12.7%) | 343 (31.8%) | |
| Heat intolerance, n (%) | .002 | |||
| Low | 336 (21.4%) | 97 (19.9%) | 239 (22.2%) | |
| Medium | 942 (60.1%) | 276 (56.6%) | 666 (61.7%) | |
| High | 289 (18.4%) | 115 (23.6%) | 174 (16.1%) | |
| Cold sensation, n (%) | <.001 | |||
| No | 844 (53.9%) | 346 (70.9%) | 498 (46.2%) | |
| Yes | 723 (46.1%) | 142 (29.1%) | 581 (53.8%) | |
| Heat sensation, n (%) | <.001 | |||
| No | 993 (63.4%) | 352 (72.1%) | 641 (59.4%) | |
| Yes | 574 (36.6%) | 136 (27.9%) | 438 (40.6%) |
Data are presented as mean ± SD or numbers (percentages).
BMI = body mass index, FFM = fat-free mass, FM = fat mass, REE = resting energy expenditure, SD = standard deviation.
P values were calculated using the t test or Chi-squared test.
3.2. Association between resting energy expenditure and thermal intolerance
Table 3 compares the mean REE across the cold/heat intolerance levels. In men, the mean REE was significantly different according to the level of cold intolerance (unadjusted: P < .001, adjusted for age and FFM: P = .001, adjusted for age, FFM, and FM: P = .003). The mean REE toward high cold intolerance decreased significantly (P value for trend; unadjusted: P < .001, adjusted for age and FFM: P < .001, adjusted for age, FFM, and FM: P = .001). Regarding heat intolerance, mean differences across the levels were significant in unadjusted (P < .001) and adjusted analyses for age and FFM (P = .028), but not in adjusted analyses for age, FFM, and FM. The mean REE toward high heat intolerance increased significantly (P for trend; unadjusted: P < .001, adjusted for age and FFM: P = .009, adjusted for age, FFM, and FM: P = .037).
Table 3.
Unadjusted and adjusted mean REEs according to the level of cold and heat intolerance stratified by sex.
| Low | Medium | High | P value* | P for trend† | |
|---|---|---|---|---|---|
| Men (n = 488) | |||||
| Cold intolerance | |||||
| Unadjusted | 1990.0 ± 27.3a | 1884.7 ± 18.2b | 1713.1 ± 39.7c | <.001 | <.001 |
| Adjusted for age and FFM | 1950.5 ± 22.9a | 1884.3 ± 15.2b | 1798.6 ± 33.7b | .001 | <.001 |
| Adjusted for age, FFM, and FM | 1942.6 ± 22.8a | 1887.2 ± 15.0ab | 1801.6 ± 33.3b | .003 | .001 |
| Heat intolerance | |||||
| Unadjusted | 1782.0 ± 31.5a | 1868.0 ± 18.7a | 2039.0 ± 29.0b | <.001 | <.001 |
| Adjusted for age and FFM | 1849.1 ± 27.1a | 1882.6 ± 15.8ab | 1947.3 ± 25.4b | .028 | .009 |
| Adjusted for age, FFM, and FM | 1857.0 ± 26.9 | 1884.5 ± 15.7 | 1936.0 ± 25.3 | .099 | .037 |
| Women (n = 1079) | |||||
| Cold intolerance | |||||
| Unadjusted | 1432.7 ± 22.8a | 1381.0 ± 9.7a | 1328.5 ± 13.0b | <.001 | <.001 |
| Adjusted for age and FFM | 1399.9 ± 20.2 | 1374.8 ± 8.5 | 1350.3 ± 11.5 | .071 | .021 |
| Adjusted for age, FFM, and FM | 1395.4 ± 20.1 | 1372.5 ± 8.4 | 1356.1 ± 11.5 | .217 | .083 |
| Heat intolerance | |||||
| Unadjusted | 1384.6 ± 15.6a | 1345.0 ± 9.3a | 1443.7 ± 18.2b | <.001 | .058 |
| Adjusted for age and FFM | 1390.2 ± 13.7ab | 1352.7 ± 8.2a | 1406.4 ± 16.2b | .003 | .761 |
| Adjusted for age, FFM, and FM | 1395.1 ± 13.6a | 1353.5 ± 8.1b | 1396.6 ± 16.2a | .006 | .697 |
Data are presented as mean ± standard error.
FFM = fat-free mass; FM = fat mass, REEs = resting energy expenditures.
P values were generated from the analysis of covariance.
P values for trend were generated from the multiple linear regression analysis.
Different letters indicate a statistically significant difference according to the level of cold and heat intolerance (P < .05).
In women, a significant mean difference in REE was found according to the level of cold intolerance in the unadjusted analysis (P < .001). A significant linear trend between cold intolerance and REE among women was also observed in unadjusted analysis (P for trend < .001) and analysis adjusted for age and FFM (P value for trend = .021). However, this association was not statistically significant after additionally adjusting for FM. Statistically significant mean differences were observed across the level of heat intolerance in women (unadjusted: P < .001, adjusted for age and FFM: P = .003, adjusted for age, FFM, and FM: P = .006), whereas the test for linear trend was not significant.
3.3. Association between resting energy expenditure and thermal sensation
The association between REE and thermal sensation is shown in Table 4. The adjusted mean REE of men who experienced cold sensation was significantly lower than that of those who experienced no cold sensations in the unadjusted analysis (P = .026) but not in the adjusted analysis. Significant mean differences according to the level of heat sensation were observed in men (unadjusted: P = .029, adjusted for age and FFM: P = .032, adjusted for age, FFM, and FM: P = .046). Cold sensation was significantly associated with REE among women (unadjusted: P = .009, adjusted for age and FFM: P = .032, adjusted for age, FFM, and FM: P = .023). A significant association between heat sensation and REE was not found in women.
Table 4.
Unadjusted and adjusted mean REEs according to the level of cold and heat sensation stratified by sex.
| No | Yes | P value* | |
|---|---|---|---|
| Men (n = 488) | |||
| Cold sensation | |||
| Unadjusted | 1912.0 ± 17.3 | 1840.5 ± 26.9 | .026 |
| Adjusted for age and FFM | 1892.4 ± 14.3 | 1888.2 ± 22.6 | .875 |
| Adjusted for age, FFM, and FM | 1890.9 ± 14.1 | 1891.9 ± 22.3 | .968 |
| Heat sensation | |||
| Unadjusted | 1871.4 ± 17.1 | 1942.5 ± 27.5 | .029 |
| Adjusted for age and FFM | 1875.2 ± 14.0 | 1932.4 ± 22.6 | .032 |
| Adjusted for age, FFM, and FM | 1876.5 ± 13.8 | 1929.2 ± 22.3 | .046 |
| Women (n = 1079) | |||
| Cold sensation | |||
| Unadjusted | 1390.5 ± 10.9 | 1351.8 ± 10.1 | .009 |
| Adjusted for age and FFM | 1384.7 ± 9.5 | 1356.8 ± 8.8 | .032 |
| Adjusted for age, FFM, and FM | 1385.5 ± 9.4 | 1356.1 ± 8.7 | .023 |
| Heat sensation | |||
| Unadjusted | 1373.9 ± 9.6 | 1363.4 ± 11.6 | .486 |
| Adjusted for age and FFM | 1371.3 ± 8.4 | 1367.3 ± 10.2 | .760 |
| Adjusted for age, FFM, and FM | 1372.2 ± 8.3 | 1365.9 ± 10.1 | .634 |
Data are presented as mean ± standard error.
FFM = fat-free mass; FM = fat mass, REEs = resting energy expenditures.
P values were generated from the analysis of covariance.
4. Discussion
This study aimed to explore the association between perceived thermal sensitivity and REE. Our findings suggest that the association between thermal sensitivity and REE differed according to sex and the dimensions of thermal sensitivity (i.e., cold intolerance, heat intolerance, cold sensation, and heat sensation). After adjusting for age, FFM, and FM, the association between cold sensation in the body and REE was significant in women, and the associations between the other dimensions of thermal sensitivity (cold/heat intolerance and heat sensation) were significant in men.
In this study, the proportion of women who had high cold intolerance was higher than that in men, whereas the proportion of men who had high heat intolerance was higher than that in women. In previous studies, women were found to be more sensitive to low temperatures and preferred slightly warmer conditions than men,[26] which is consistent with our results. However, the results of previous studies on sex differences in heat intolerance are inconsistent. Although some studies have reported that, compared to men, women are less tolerant to deviation from the optimal temperature and complain more about the ambient low and high temperatures[26]; some studies have reported that compared to women, more men experienced heat and felt uncomfortable at high temperatures.[27,28] Studies on the thermoneutral zone have also reported that lower critical temperature (the ambient temperature below which the rate of metabolic heat production increases) is higher in women than in men, whereas it is unclear whether the upper critical temperature (the ambient temperature above which the rate of evaporative heat loss increases) is also higher in women than that in men.[29]
Regarding thermal sensation, in this study, more women experienced both cold and heat sensations in the body than men. This result seems partially contradictory to the previous report that the proportion of women with cold sensations in their body was larger than that of men, and the proportion of women with warm sensations in their body was smaller than that of men when they were instructed to select whether their hands, legs, and abdomen are generally cold or warm.[9] Previous studies that investigated a cutaneous thermal sensitivity to a cold and warm stimulus reported that women are more sensitive to both cold and warm stimulations than men, and women are more sensitive to cold stimulation compared to warm stimulation.[30,31] Moreover, women have more complaints of discomfort from cold hands and feet[32,33] and have a lower distal skin temperature at least in the cold than men,[34,35] but they have higher upper body skin temperatures than men.[36] Some studies have reported that women may have a greater skin blood flow during passive body heating, as they depend more on cutaneous vasodilation for heat loss during passive body heating than on sweating, men,[37] which might induce increased perceived heat sensations in the body at high temperatures. Taken together, women might tend to experience higher cold and heat sensations than men; however, a relatively greater magnitude of cold sensation than heat sensation in women sometimes seems to cause heat sensation to be neglected in women.[9]
Thermal sensation in the body is a crucial factor that might affect thermal intolerance. However, our results suggest the need to distinguish the 4 different dimensions of perceived thermal sensitivity (i.e., cold intolerance, heat intolerance, cold sensation, and heat sensation) in their relationship with REE in each sex.
Men with higher cold intolerance tended to have lower REE, whereas men with higher heat intolerance tended to have higher REE. When exposed to cold, protective mechanisms against hypothermia, including muscle shivering and cutaneous vasoconstriction, occur to produce heat or increase insulation. However, muscle shivering and cold sensation in body parts impede coordinated movements and cause discomfort.[38] As lower REE means lower endogenous heat production,[5] individuals with lower REE who are exposed to cold might experience these responses earlier or stronger than others to compensate for their lower heat production, which might lead to higher cold intolerance. Conversely, individuals with higher endogenous heat production (i.e., higher REE) might be more vulnerable in a hot environment to reach heat balance in the body, which might lead to a higher heat intolerance. In women, the trend of the association between cold intolerance and REE was similar and significant when unadjusted or adjusted for age and FFM. However, it was only marginally significant when additionally adjusted for FM, which means that the significantly lower REE in women with high cold intolerance when adjusted for age and FFM, might be mediated by reduced insulation due to their smaller FM.
The differences in the association between cold/heat intolerance and REE with respect to sex might be due to the different thermoregulatory responses to cold or heat stress according to sex. Compared to women, men tend to use the strategy of shivering thermogenesis in cold stress[39] and evaporative heat loss via sweating during heat stress to reach their thermal balance rather than controlling cutaneous blood perfusion.[37] Shivering and sweating might be directly related to the level of perceived feeling of intolerance to cold and heat.[38] This might lead to a stronger association between cold/heat intolerance and REE in men than women.
Regarding cold/heat sensation, women with cold sensation in their bodies had lower REE than women without it, and men with increased heat sensation in their bodies had higher REE than men without it. It could be hypothesized that women with lower REE might compensate for their lower heat production in cold stress with increased insulation by cutaneous vasoconstriction to reach a thermal balance in their body and men with higher REE might compensate for their higher heat production in heat stress with increased convective heat loss through vasodilation. In cold stress, women tend to use the strategy of increased insulative response through vasoconstriction rather than shivering thermogenesis compared to men[39] which might result in a stronger association between cold sensation and REE in women than that in men. The reason for the stronger association between heat sensation and REE in men than that in women is unclear as men tend to use the strategy of increased sweating rather than vasodilation in heat stress when compared to women.[37] This might be related to the fact that previous reports on sex differences regarding heat sensation have revealed mixed results as mentioned above.[9,30,31] This needs to be further clarified in future studies.
Thermal sensitivity has been related to several disorders, including Raynaud phenomenon, perimenopausal syndrome, and thyroid disorders.[40–42] However, the possible utility of individual differences in thermal sensitivity for assessing risks or stratifying patients in a wider scope of diseases, such as ocular diseases, metabolic syndrome, functional dyspepsia, multiple sclerosis, breast cancer, insomnia, and affective disorders[11,32,33,43–46] has recently been reported. Several mechanisms have been suggested concerning the association between thermal sensitivity and diseases, including deficiencies in vascular regulation, brain function in comfort sensing, sympathovagal balance, or changes in adiponectin level.[10,43,47,48] As our results suggest that thermal sensitivity is associated with REE level, REE could also be considered when exploring the underlying mechanism of the association between thermal sensitivity and diseases.
One strength of our study lies in its comprehensive coverage of multiple domains of perceived thermal sensitivity, encompassing both thermal intolerance and sensation within each sense (cold and heat). This allows for a thorough examination of their respective relationships with REE. Previous studies have often focused solely on 1 dimension, such as cold sensation, or on syndromes diagnosed by various symptoms, not limited to those related to thermal sensitivity (e.g., Heat syndrome of traditional East Asian medicine).[8,15] Additionally, our study benefits from a large sample size comprising both men and women, facilitating comparative analyses between sexes.
Some limitations should be considered while interpreting our results. First, due to the cross-sectional nature of this study design, causal inferences cannot be considered. Second, sample size calculation could not be conducted before the study, since we have extracted relevant data from the KME study, which aimed to build a large data infrastructure based on Korean Medicine. Third, we used a face mask as a gas collection device. The face mask may cause discomfort to the participant, leading to the overestimation of the REE than that by the canopy method[49]; however, other studies have also reported that the face mask method attains comparable stability and reliability to the canopy method.[50] Fourth, our study did not investigate the menstrual cycles of women, changes in weight, and thyroid hormone levels. The menstrual cycle, changes in body weight, and subclinical changes in thyroid function might affect the REE, although this study excluded individuals diagnosed with thyroid diseases. Therefore, consideration of the menstrual cycle of women, changes in body weight, and thyroid function is recommended in future studies. Fifth, the reliance on self-reported measures of perceived thermal sensitivity introduces inherent limitations, including potential reporting biases and susceptibility to psychological influences. Despite these limitations, perceived thermal sensitivity has demonstrated its value in predicting physiological responses to thermal exposure,[8,20] and has facilitated large-scale studies due to the impracticality of objective measures. Sixth, our analysis did not account for the potential effects of medications, other than those for diabetes and hypertension, on REE or thermal sensitivity. Nevertheless, our study focused on healthy individuals, excluding patients diagnosed with various conditions such as cardiovascular diseases, mental illnesses, and thyroid diseases, as well as individuals on medication for diabetes or hypertension. These exclusions were made as these conditions and medications are prevalent and may significantly influence REE.[22–24,51] Lastly, the findings cannot be generalized to patients with diseases or people with 2 strong values within each thermal sensitivity category that were not included in this study. The association between thermal sensitivity and REE in them should be investigated separately in future studies.
5. Conclusion
Although lower REE was generally related to higher cold sensitivity and lower heat sensitivity in both sexes and vice versa, after adjusting for confounders, the significance differed according to sex and the 4 dimensions of thermal sensitivity (i.e., cold intolerance, heat intolerance, cold sensation, and heat sensation). The association between cold sensation and REE was significant in women, and the association between the other 3 dimensions and REE was significant in men.
Acknowledgments
The authors thank Naju Dongshin University Korean Medicine Hospital, Pusan National University Korean Medicine Hospital, Gachon University Gil Medical Center, Dongguk University Ilsan Oriental Hospital, and Dunsan Korean Medicine Hospital of Daejeon University for their support.
Author contributions
Conceptualization: Sujeong Mun, Junghun Yoo, Jeong Hwan Park.
Methodology: Sujeong Mun, Junghun Yoo, Mi Hong Yim.
Validation: Sujeong Mun, Mi Hong Yim.
Writing—original draft: Sujeong Mun, Junghun Yoo.
Data curation: Junghun Yoo, Soyoung Kim, Daehyeok Kim, Min-Ji Kim.
Formal analysis: Junghun Yoo.
Funding acquisition: Sanghun Lee.
Project administration: Sanghun Lee, Youngseop Lee, Jeong Hwan Park.
Supervision: Sanghun Lee, Youngseop Lee.
Writing—review & editing: Sanghun Lee, Youngseop Lee, Jeong Hwan Park.
Investigation: Soyoung Kim, Daehyeok Kim, Min-Ji Kim, Jeong Hwan Park.
Resources: Soyoung Kim, Daehyeok Kim, Min-Ji Kim.
Abbreviations:
- BMI
- body mass index
- FFM
- fat-free mass
- FM
- fat mass
- KME
- Korea Medicine Examination
- REE
- resting energy expenditure
This research was funded by the Collection of Clinical Big Data and Construction of Service Platform for Developing Korean Medicine Doctor with Artificial Intelligence (grant number KSN2021110) and Development of Korean Medicine Original Technology for Preventive Treatment based on Integrative Big Data (grant number KSN2023120) from the Korea Institute of Oriental Medicine.
The authors have no conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
How to cite this article: Mun S, Yoo J, Lee S, Yim MH, Kim S, Kim D, Kim M-J, Lee Y, Park JH. Resting energy expenditure differs among individuals with different levels of perceived thermal sensitivity: A cross-sectional study. Medicine 2024;103:21(e38293).
SM and JY contributed equally to this work.
Contributor Information
Sujeong Mun, Email: azrain@kiom.re.kr.
Junghun Yoo, Email: yoojh4@kihasa.re.kr.
Sanghun Lee, Email: rheey119@kiom.re.kr.
Mi Hong Yim, Email: mh.yim@kiom.re.kr.
Soyoung Kim, Email: hohomin12@kiom.re.kr.
Daehyeok Kim, Email: hohomin12@kiom.re.kr.
Min-Ji Kim, Email: hohomin12@kiom.re.kr.
Youngseop Lee, Email: rheey119@kiom.re.kr.
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