Ambient temperature and prevalence of obesity in the Spanish population: The Di@bet.es study

Environmental mixtures and body mass index in two prospective US-based cohorts of female nurses

We estimated the joint effect of particulate matter ≤ 2.5 µm in diameter (PM2.5), nitrogen dioxide (NO2), seasonal temperature, noise, greenness, light at night, and neighborhood socioeconomic status (NSES) on body mass index (BMI) in a mixture context among 194,966 participants from the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII) over 30 years. BMI was calculated from self-reported weight and height. Single- and multi-exposure generalized estimating equations models were used to estimate the difference in BMI per interquartile range (IQR) increase of environmental factors, and quantile g-computation methods were used to estimate joint associations. In both cohorts, we consistently observed positive associations of BMI with PM2.5 and NO2 concentrations as well as negative associations with light at night and NSES regardless modeling approach. A positive association with noise was only observed in NHS. Negative associations with greenness and winter temperature were only observed in NHSII. Overall, the changes in BMI per quintile increase in all eight exposures were -0.11 (-0.13, -0.08) in NHS and -0.39 (-0.41, -0.37) in NHSII, which were largely driven by air pollution and nighttime noise (18-45 %) in the positive direction and NSES (>70 %) in the negative direction. Future intervention on environmental factors, especially reducing PM2.5, NO2 and noise or improving the NSES, might be helpful to lower BMI.

Review: Phenotypic and molecular evidence of inter- and trans-generational effects of heat stress in livestock mammals and humans

Internal and external factors can change an individual's phenotype. A significant external threat to humans and livestock is environmental heat load, a combination of high ambient temperatures and humidity. A heat stress response occurs when an endothermal animal is exposed to a heat load that challenges its' thermoregulation capacity. With the ongoing climate change trends, the incidence of chronically elevated temperatures causing heat stress is expected to rise, posing an even greater risk to the health and survival of all species. Heat stress is generally related to adverse effects on food intake, health, and performance in mammal livestock species and humans. Evidence from epidemiological and experimental studies of humans and livestock demonstrated that exposing pregnant females to heat stress affects the phenotype of the newborn in various ways. For instance, in utero heat stress is related to lower BW at birth and changes in metabolic and immune functions in the newborn. In cows, the effects of heat stress on the performance of the offspring last for three or four generations, suggesting intergenerational effects. The molecular mechanism orchestrating these effects of heat stress may be epigenetic regulation, as various epigenetic mechanisms control genome reprogramming. Epigenetic modifications are attached to DNA and histone proteins and can influence how specific genes are expressed, resulting in phenotypic changes. Epigenetic modifications can be triggered in response to environmental heat stress without altering the DNA sequence. Heat stress insults during critical periods of organ development (i.e., fetal exposure) can trigger epigenetic modifications that impact health and productivity across generations. Thus, epigenetic changes caused by extreme temperatures can be passed down to the offspring if the mother is exposed to the insult during pregnancy. Understanding the phenotypic and molecular consequences of maternal heat stress, including the carry-over lingering effects on the resulting progeny, is necessary to develop effective mitigation strategies and gain translational knowledge about the fundamental processes leading to intergenerational and transgenerational inheritance. This review examines the phenotypic and molecular evidence of how maternal exposure to extreme heat can affect future generations in several species, including humans, swine, sheep, goats, and cattle. The current knowledge of the molecular mechanisms involved in intergenerational and transgenerational epigenetic inheritance will also be presented and discussed.

Sex-specific associations of environmental exposures with prevalent diabetes and obesity - Results from the KORA Fit study

Promising evidence suggests a link between environmental factors, particularly air pollution, and diabetes and obesity. However, it is still unclear whether men and women are equally susceptible to environmental exposures. Therefore, we aimed to assess sex-specific long-term effects of environmental exposures on metabolic diseases. We analyzed cross-sectional data from 3,034 participants (53.7% female, aged 53-74 years) from the KORA Fit study (2018/19), a German population-based cohort. Environmental exposures, including annual averages of air pollutants [nitrogen oxides (NO2, NOx), ozone, particulate matter of different diameters (PM10, PMcoarse, PM2.5), PM2.5abs, particle number concentration], air temperature and surrounding greenness, were assessed at participants' residences. We evaluated sex-specific associations of environmental exposures with prevalent diabetes, obesity, body-mass-index (BMI) and waist circumference using logistic or linear regression models with an interaction term for sex, adjusted for age, lifestyle factors and education. Further effect modification, in particular by urbanization, was assessed in sex-stratified analyses. Higher annual averages of air pollution, air temperature and greenness at residence were associated with diabetes prevalence in men (NO2: Odds Ratio (OR) per interquartile range increase in exposure: 1.49 [95% confidence interval (CI): 1.13, 1.95], air temperature: OR: 1.48 [95%-CI: 1.15, 1.90]; greenness: OR: 0.78 [95%-CI: 0.59, 1.01]) but not in women. Conversely, higher levels of air pollution, temperature and lack of greenness were associated with lower obesity prevalence and BMI in women. After including an interaction term for urbanization, only higher greenness was associated with higher BMI in rural women, whereas higher air pollution was associated with higher BMI in urban men. To conclude, we observed sex-specific associations of environmental exposures with metabolic diseases. An additional interaction between environmental exposures and urbanization on obesity suggests a higher susceptibility to air pollution among urban men, and higher susceptibility to greenness among rural women, which needs corroboration in future studies.

Downregulated Adipose Tissue Expression of Browning Genes With Increased Environmental Temperatures

CONTEXT

Climate change and global warming have been hypothesized to influence the increased prevalence of obesity worldwide. However, the evidence is scarce.

OBJECTIVE

We aimed to investigate how outside temperature might affect adipose tissue physiology and metabolic traits.

METHODS

The expression of genes involved in thermogenesis/browning and adipogenesis were evaluated (through quantitative polymerase chain reaction) in the subcutaneous adipose tissue (SAT) from 1083 individuals recruited in 5 different regions of Spain (3 in the North and 2 in the South). Plasma biochemical variables and adiponectin (enzyme-linked immunosorbent assay) were collected through standardized protocols. Mean environmental outdoor temperatures were obtained from the National Agency of Meteorology. Univariate, multivariate, and artificial intelligence analyses (Boruta algorithm) were performed.

RESULTS

The SAT expression of genes associated with browning (UCP1, PRDM16, and CIDEA) and ADIPOQ were significantly and negatively associated with minimum, average, and maximum temperatures. The latter temperatures were also negatively associated with the expression of genes involved in adipogenesis (FASN, SLC2A4, and PLIN1). Decreased SAT expression of UCP1 and ADIPOQ messenger RNA and circulating adiponectin were observed with increasing temperatures in all individuals as a whole and within participants with obesity in univariate, multivariate, and artificial intelligence analyses. The differences remained statistically significant in individuals without type 2 diabetes and in samples collected during winter.

CONCLUSION

Decreased adipose tissue expression of genes involved in browning and adiponectin with increased environmental temperatures were observed. Given the North-South gradient of obesity prevalence in these same regions, the present observations could have implications for the relationship of the obesity pandemic with global warming.

High-fat diet feeding disrupts the coupling of thermoregulation to energy homeostasis

OBJECTIVE

Preserving core body temperature across a wide range of ambient temperatures requires adaptive changes of thermogenesis that must be offset by corresponding changes of energy intake if body fat stores are also to be preserved. Among neurons implicated in the integration of thermoregulation with energy homeostasis are those that express both neuropeptide Y (NPY) and agouti-related protein (AgRP) (referred to herein as AgRP neurons). Specifically, cold-induced activation of AgRP neurons was recently shown to be required for cold exposure to increase food intake in mice. Here, we investigated how consuming a high-fat diet (HFD) impacts various adaptive responses to cold exposure as well as the responsiveness of AgRP neurons to cold.

METHODS

To test this, we used immunohistochemistry, in vivo fiber photometry and indirect calorimetry for continuous measures of core temperature, energy expenditure, and energy intake in both chow- and HFD-fed mice housed at different ambient temperatures.

RESULTS

We show that while both core temperature and the thermogenic response to cold are maintained normally in HFD-fed mice, the increase of energy intake needed to preserve body fat stores is blunted, resulting in weight loss. Using both immunohistochemistry and in vivo fiber photometry, we show that although cold-induced AgRP neuron activation is detected regardless of diet, the number of cold-responsive neurons appears to be blunted in HFD-fed mice.

CONCLUSIONS

We conclude that HFD-feeding disrupts the integration of systems governing thermoregulation and energy homeostasis that protect body fat mass during cold exposure.

A Review of the Role of Built Environment and Temperature in the Development of Childhood Obesity

The burden of obesity is rising globally and is studied widely, yet the evidence for the association of environmental factors (both built and natural) with childhood obesity remains inconsistent. A relation with temperature as a proxy for natural environmental factors for obesity has not been reviewed previously. The purpose of this review was to assimilate updated evidence on environmental factors of childhood obesity. Three databases, MEDLINE (Medical Literature Analysis and Retrieval System Online), Web of Science, and Cochrane, were searched for articles related to the effect of built environment and temperature on childhood obesity in 6-12-year-olds published in the last five years. Twelve studies were identified: four longitudinal and eight cross-sectional. The studies were appraised using the National Institute of Health Quality (NIH) Assessment Tool. A review of included studies showed that built environmental features like higher residential and population density, higher intersection density, more playgrounds, and all park features like the presence or availability of parks, high number of parks, proximity to parks, and an increased park land area, showed a protective association against childhood obesity while land use mix showed a promoting association for the development of childhood obesity. Inconclusive evidence was observed for other built environmental features. The search strategy did not retrieve any literature published in the past five years studying the association between temperature and the development of childhood obesity. Standardization of definitions of exposure and outcome measures is recommended. Further research studying the relationship between environmental temperature and the development of childhood obesity is recommended.

The association between childhood adiposity in northeast China and anthropogenic heat flux: A new insight into the comprehensive impact of human activities

Anthropogenic heat has been reported to have significant health impacts, but research on its association with childhood adiposity is still lacking. In this study, we matched the 2008-2012 average anthropogenic heat flux, as simulated by a grid estimation model using inventory methods, with questionnaire and measurement data of 49,938 children randomly recruited from seven cities in Northeast China in 2012. After adjusting for social demographic and behavioral factors, we used generalized linear mixed-effect models to assess the association between anthropogenic heat flux and adiposity among children. We also examined the effect modification of various social demographic and behavioral confounders. We found that each 10 W/m2 increase in total anthropogenic heat flux and that from the industry source was associated with an increase of 5.82% (95% CI = 0.84%-11.05%) and 6.62% (95% CI = 0.87%-12.70%) in the odds of childhood adiposity. Similarly, the excess rate of adiposity among children were 5.26% (95% CI = -1.33%-12.29%) and 8.51% (95% CI = 2.24%-15.17%) per 1 W/m2 increase in the anthropogenic heat flux from transportation and buildings, and was 7.94% (95% CI = 2.28%-13.91%) per 0.001 W/m2 increase in the anthropogenic heat flux from human metabolism. We also found generally greater effect estimates among female children and children who were exposed to passive smoking during pregnancy, born by caesarean section, non-breastfed/mixed-fed, or lived within 20 m adjacent to the main road. The potential deleterious effect of anthropogenic heat exposure on adiposity among children may make it a new but major threat to be targeted by future mitigation strategies.

Socio-geographical disparities of obesity and excess weight in adults in Spain: insights from the ENE-COVID study

Background

In Spain, differences in the prevalence of obesity and excess weight according to sex and sociodemographic factors have been described at the national level, although current data do not allow to delve into geographical differences for these conditions. The aim was to estimate national and regional prevalences of adult obesity and excess weight in Spain by sex and sociodemographic characteristics, and to explore difference sources of inequalities in its distribution, as well as its geographical pattern.

Method

ENE-COVID study was a nationwide representative seroepidemiological survey with 57,131 participants. Residents in 35,893 households were selected from municipal rolls using a two-stage random sampling stratified by province and municipality size (April-June 2020). Participants (77.0% of contacted individuals) answered a questionnaire which collected self-reported weight and height, as well as different socioeconomic variables, that allowed estimating crude and standardized prevalences of adult obesity and excess weight.

Results

Crude prevalences of obesity and excess weight were higher in men (obesity: 19.3% vs. 18.0%; excess weight: 63.7% vs. 48.4%), while severe obesity was more prevalent in women (4.5% vs. 5.3%). These prevalences increased with age and disability, and decreased with education, census tract income and municipality size. Differences by educational level, relative census income, nationality or disability were clearly higher among women. Obesity by province ranged 13.3-27.4% in men and 11.4-28.1% in women; excess weight ranged 57.2-76.0% in men and 38.9-59.5% in women. The highest prevalences were located in the southern half of the country and some north-western provinces. Sociodemographic characteristics only explained a small part of the observed geographical variability (25.2% obesity).

Conclusion

Obesity and overweight have a high prevalence in Spain, with notable geographical and sex differences. Socioeconomic inequalities are stronger among women. The observed geographical variability suggests the need to implement regional and local interventions to effectively address this public health problem.

Challenging obesity and sex based differences in resting energy expenditure using allometric modeling, a sub-study of the DIETFITS clinical trial

BACKGROUND & AIMS

Resting energy expenditure (REE) is a major component of energy balance. While REE is usually indexed to total body weight (BW), this may introduce biases when assessing REE in obesity or during weight loss intervention. The main objective of the study was to quantify the bias introduced by ratiometric scaling of REE using BW both at baseline and following weight loss intervention.

DESIGN

Participants in the DIETFITS Study (Diet Intervention Examining The Factors Interacting with Treatment Success) who completed indirect calorimetry and dual-energy X-ray absorptiometry (DXA) were included in the study. Data were available in 438 participants at baseline, 340 at 6 months and 323 at 12 months. We used multiplicative allometric modeling based on lean body mass (LBM) and fat mass (FM) to derive body size independent scaling of REE. Longitudinal changes in indexed REE were then assessed following weight loss intervention.

RESULTS

A multiplicative model including LBM, FM, age, Black race and the double product (DP) of systolic blood pressure and heart rate explained 79% of variance in REE. REE indexed to [LBM^0.66 × FM^0.066] was body size and sex independent (p = 0.91 and p = 0.73, respectively) in contrast to BW based indexing which showed a significant inverse relationship to BW (r = -0.47 for female and r = -0.44 for male, both p < 0.001). When indexed to BW, significant baseline differences in REE were observed between male and female (p < 0.001) and between individuals who are overweight and obese (p < 0.001) while no significant differences were observed when indexed to REE/[LBM^0.66 × FM^0.066], p > 0.05). Percentage predicted REE adjusted for LBM, FM and DP remained stable following weight loss intervention (p = 0.614).

CONCLUSION

Allometric scaling of REE based on LBM and FM removes body composition-associated biases and should be considered in obesity and weight-based intervention studies.

Joint exposure to air pollution, ambient temperature and residential greenness and their association with metabolic syndrome (MetS): A large population-based study among Chinese adults

Previous studies assessing adverse health have traditionally focused on a single environmental exposure, failing to reflect the reality of various exposures present simultaneously. Air pollution, ambient temperature and greenness have been proposed as critical environmental factors associated with metabolic syndrome (MetS). However, evidence exploring their joint relationships with MetS is needed for identifying interactive factors and developing more targeted public health interventions. The baseline data was obtained from China Multi-Ethnic Cohort (CMEC). Environmental data of air pollutants (PM_2.5, O₃) and NDVI for greenness was calculated from satellites data. Ambient temperature data were obtained from European Center for Medium-Range Weather Forecasts (ECMWF). MetS was classified based on National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) using anthropometric measures and biomarkers. Logistic regression models were utilized to examine the combined relationship of MetS with three-year exposure to air pollutants, temperature and NDVI. Relative excess risk due to interaction (RERI) was calculated to evaluate interaction on an additive scale. We found associations between prevalent MetS and interquartile range (IQR) increases in PM_2.5 (OR: 1.38; 95% confidence interval [95% CI]: 1.23, 1.55) and O₃ (OR: 1.15; 95% CI: 1.09, 1.22). Additive and multiplicative interactions were observed between air pollutants and temperature exposure. Compared to low-temperature level, the relationship between PM_2.5 and MetS attenuated (RERI: 0.22, 95% CI: 0.44, -0.04) at high-temperature level, while the relationship between O₃ and MetS enhanced (RERI: 0.05, 95% CI: 0.02, 0.11). At low NDVI 250 m, the association between PM_2.5 and MetS was stronger (RERI: 0.13, 95% CI: 0.05, 0.19) with high NDVI 250 m as the reference group. Our findings showed that ambient temperature and residential greenness could affect the relationship between air pollutants and MetS.

Revisioning Obesity in Health Care Practice and Research: New Perspectives on the Role of Body Temperature

Obesity is a leading health problem in the United States and globally. Relatively few people with obesity achieve long-term weight control, suggesting that obesity and resistance to weight change represent functional adaption of energy homeostasis to the environment. The purpose of this article is to synthesize the literature regarding the relationship between environmental temperature and body weight and fat mass to provide a new explanation of obesity as a problem of maintaining core body temperature. Chronic exposure to cool environmental temperatures likely contributed to the obesity epidemic, and passive whole-body warming may be a promising intervention for weight control.

Analysis of Spatial Distribution of CVD and Multiple Environmental Factors in Urban Residents

Cardiovascular disease (CVD) poses a serious threat to urban health with the development of urbanization. There are multifaceted and comprehensive influencing factors for CVD, so clarifying the spatial distribution characteristics of CVD and multiple environmental influencing factors is conducive to improving the active health intervention of urban environment and promoting the sustainable development of cities The spatial distribution characteristics of CVD deaths in a certain district, Bengbu City, Huaihe River Basin, China, in 2019 were explored, and the correlation between multiple environmental factors and CVD mortality was investigated in this study, to reveal the action mechanism of multiple environmental factors affecting the risk of mortality. Relevant studies have shown that (1) CVD deaths are characterized as follows: male deaths are more than females; the mortality is higher in those of higher age; most of them are unemployed; cardiocerebral infarction is the main cause of death; and the deaths are mainly distributed in the central city and near the old urban area. (2) The increased CVD mortality can be attributed to the increased density of restaurants and cigarette and wine shops around the residential area, the increased traffic volume, the dense residential and spatial forms, the low green space coverage, and the distance from rivers. Therefore, appropriate urban planning and policies can improve the active health interventions in cities and reduce CVD mortality.

Postnatal exposure to ambient temperature and rapid weight gain among infants delivered at term gestations: a population-based cohort study

BACKGROUND

The global prevalence of childhood obesity has risen dramatically recently. Previous studies found an association between rapid infant weight gain and childhood overweight. Evidence suggests that exposure to high ambient air temperatures during prenatal life and during adulthood is associated with birthweight and obesity respectively.

OBJECTIVE

The objective of this study was to examine whether exposure to high ambient temperatures during infancy is associated with rapid infant weight gain in Israel.

METHODS

This is a population-based historical cohort study using data from the Israeli national public network of maternal and child health clinics between 2008 and 2013. We assessed exposure to ambient temperature in the first year of life using a high-resolution hybrid spatio-temporal model and calculated annual mean and minimum temperatures for each infant based on daily mean and minimum temperatures at the community clinic location. We defined rapid infant weight gain as a World Health Organization weight z-score difference >0.67 between birthweight and weight at age one year. We estimated these associations using log-linear and general additive models and adjusted for population group, district, maternal age, parental education, parity, sex, gestational age, birthweight, calendar year and calendar month of birth.

RESULTS

The study population included 217,310 singleton-term infants. Adjusted models demonstrated a positive association between ambient temperature exposure and rapid infant weight gain. Compared to the third quintile of minimum temperature, infants exposed to the first and second quintile had an adjusted relative risk of 0.98 (95% CI 0.96, 1.00) and 0.97 (95% CI 0.95, 0.98), respectively, while those exposed to the fourth and fifth quintiles had an adjusted relative risk of 1.06 (95% CI 1.04, 1.07) and 1.02 (95% CI 1.00, 1.04) respectively. The associations with mean temperature were similar but slightly weaker.

CONCLUSIONS

Exposure to higher ambient temperatures, of emerging importance in the climate change era, is associated with rapid infant weight gain in Israel. Future studies should use additional exposure, covariate, and outcome data to analyse the nature and the source of this association in more detail.

Arcuate proopiomelanocortin is part of a novel neural connection for short-term low-degree of high ambient temperature effects on food intake

High ambient temperature (HTa) is an important environmental factor influencing food intake (FI). We previously demonstrated that low-degree HTa exposure decreased FI earlier than activated physiological responses, and this effect was related to the median preoptic nucleus (MnPO) and arcuate nucleus (Arc) connection. The present study refines the condition of low-degree HTa exposure and focuses on the mechanism of Arc neural activation. We demonstrated in the first experiment that with the usual ambient temperature (Ta) at 23 °C, the low degree HTa condition is at a 7 °C temperature difference and with 90 min exposure. Rats exposed to this short-term low-degree HTa had significantly lower 1-h FI than those exposed to control Ta (CTa) without differences in rectal temperature and hematocrit. Under nonfeeding conditions, HTa could enhance c-Fos at the Arc without the activation of proopiomelanocortin (POMC) neurons. Under feeding conditions, HTa could enhance both c-Fos and POMC at Arc. In addition, the number of c-Fos and POMC colocalizations in the HTa group was higher than that in the CTa group. Finally, intracerebral preinfusion with a subthreshold dose of the melanocortin antagonist SHU9119 reversed the effect of low-degree HTa exposure on FI. Therefore, we conclude that the effect of short-term low-degree HTa exposure on FI in rats is mediated in part by activation of POMC neurons at the Arc. The results partially support the hypothesis that Arc is a crucial hypothalamic nucleus for the effect of low-degree HTa exposure on FI.

Oxygen in Metabolic Dysfunction and Its Therapeutic Relevance

Significance: In recent years, a number of studies have shown altered oxygen partial pressure at a tissue level in metabolic disorders, and some researchers have considered oxygen to be a (macro) nutrient. Oxygen availability may be compromised in obesity and several other metabolism-related pathological conditions, including sleep apnea-hypopnea syndrome, the metabolic syndrome (which is a set of conditions), type 2 diabetes, cardiovascular disease, and cancer. Recent Advances: Strategies designed to reduce adiposity and its accompanying disorders have been mainly centered on nutritional interventions and physical activity programs. However, novel therapies are needed since these approaches have not been sufficient to counteract the worldwide increasing rates of metabolic disorders. In this regard, intermittent hypoxia training and hyperoxia could be potential treatments through oxygen-related adaptations. Moreover, living at a high altitude may have a protective effect against the development of abnormal metabolic conditions. In addition, oxygen delivery systems may be of therapeutic value for supplying the tissue-specific oxygen requirements. Critical Issues: Precise in vivo methods to measure oxygenation are vital to disentangle some of the controversies related to this research area. Further, it is evident that there is a growing need for novel in vitro models to study the potential pathways involved in metabolic dysfunction to find appropriate therapeutic targets. Future Directions: Based on the existing evidence, it is suggested that oxygen availability has a key role in obesity and its related comorbidities. Oxygen should be considered in relation to potential therapeutic strategies in the treatment and prevention of metabolic disorders. Antioxid. Redox Signal. 35, 642-687.

A systematic review on the association between total and cardiopulmonary mortality/morbidity or cardiovascular risk factors with long-term exposure to increased or decreased ambient temperature

The health effects of acute exposure to temperature extremes are established; those of long-term exposure only recently received attention. We performed a systematic review to assess the associations of long-term (>3 months) exposure to higher or lower temperature on total and cardiopulmonary mortality and morbidity, screening 3455 studies and selecting 34. The studies were classified in those observing associations within a population over years with changing annual temperature indices and those comparing areas with a different climate. We also assessed the risk of bias, adapting appropriately an instrument developed by the World Health Organization for air pollution. Studies reported that annual temperature indices for extremes and variability were associated with annual increases in mortality, indicating that effects of temperature extremes cannot be attributed only to short-term mortality displacement. Studies on cardiovascular mortality indicated stronger associations with cold rather than hot temperature, whilst those on respiratory outcomes reported effects of both heat and cold but were few and used diverse health outcomes. Interactions with air pollution were not generally assessed. The few studies investigating effect modification showed stronger effects among the elderly and those socially deprived. Comparisons of health outcome prevalence between areas reported lower blood pressure and a tendency for higher obesity in populations living in warmer climates. Our review indicated interesting associations between long-term exposure to unusual temperature levels in specific areas and differences in health outcomes and cardiovascular risk factors between geographical locations with different climate, but the number of studies by design and health outcome was small. Risk of bias was identified because of the use of crude exposure assessment and inadequate adjustment for confounding. More and better designed studies, including the investigation of effect modifiers, are needed.

MECHANISMS IN ENDOCRINOLOGY: Human brown adipose tissue as a therapeutic target: warming up or cooling down?

Excessive accumulation of white adipose tissue leads to obesity and its associated metabolic health consequences such as type 2 diabetes and cardiovascular disease. Several approaches to treat or prevent obesity including public health interventions, surgical weight loss, and pharmacological approaches to reduce caloric intake have failed to substantially modify the increasing prevalence of obesity. The (re-)discovery of active brown adipose tissue (BAT) in adult humans approximately 15 years ago led to a resurgence in research into whether BAT activation could be a novel therapy for the treatment of obesity. Upon cold stimulus, BAT activates and generates heat to maintain body temperature, thus increasing energy expenditure. Activation of BAT may provide a unique opportunity to increase energy expenditure without the need for exercise. However, much of the underlying mechanisms surrounding BAT activation are still being elucidated and the effectiveness of BAT as a therapeutic target has not been realised. Research is ongoing to determine how best to expand BAT mass and activate existing BAT; approaches include cold exposure, pharmacological stimulation using sympathomimetics, browning agents that induce formation of thermogenic beige adipocytes in white adipose depots, and the identification of factors secreted by BAT with therapeutic potential. In this review, we discuss the caloric capacity and other metabolic benefits from BAT activation in humans and the role of metabolic tissues such as skeletal muscle in increasing energy expenditure. We discuss the potential of current approaches and the challenges of BAT activation as a novel strategy to treat obesity and metabolic disorders.

Effect of temperature and/or sweetness of beverages on body composition in rats

Sweetened beverages are mainly consumed cold and various processes are activated in response to external temperature variations. However, the effect of internal temperature variations through the ingestion of cold beverages is far from clear. Two experiments were conducted to investigate the effect of beverage temperature on body composition. Sprague-Dawley rats (5-6-week-old males) had free access to food and beverage for 8 weeks. Energy intake, body weight and body composition were monitored. In Expt 1, two groups of rats (n 9) consumed water at room temperature (NW about 22°C) or cold (CW about 4°C). In Expt 2, rats were offered room-temperature (N) or cold (C) sweetened water (10 % sucrose CSu (n 7) and NSu (n 8); or 0·05 % acesulfame K CAk (n 6) and NAk (n 8)) for 12 h, followed by plain water. Our results show that in Expt 1, CW had higher lean body mass (P < 0·001) and lower body fat gain (P = 0·004) as compared with NW. In Expt 2, body weight (P = 0·013) and fat (P ≤ 0·001) gains were higher in the non-energetic sweetened groups, while lean body mass was not affected by the type of sweeteners or temperature. In conclusion, cold water ingestion improved lean body mass gain and decreased fat gain because of increased energy expenditure, while non-energetic sweetener (acesulfame K) increased body fat gain due to improved energy efficiency. Internal cold exposure failed to increase energy intake in contrast to that of external cold exposure.

Long-term exposure to ambient PM2.5 and stroke mortality among urban residents in northern China

Evidence is still limited for the role of long-term PM_2.5 exposure in cerebrovascular diseases among residents in high pollution regions. The study is aimed to investigate the long-term effects of PM_2.5 exposure on stroke mortality, and further explore the effect modification of temperature variation on the PM_2.5-mortality association in northern China. Based on a cohort data with an average follow-up of 9.8 years among 38,435 urban adults, high-resolution estimates of PM_2.5 derived from a satellite-based model were assigned to each participant. A Cox regression model with time-varying exposures and strata of geographic regions was employed to assess the risks of stroke mortality associated with PM_2.5, after adjusting for individual risk factors. The cross-product term of PM_2.5 exposure and annual temperature range was further added into the regression model to test whether the long-term temperature variation would modify the association of PM_2.5 with stroke mortality. Among the study participants, the annual mean level of PM_2.5 concentration was 66.3 μg/m³ ranging from 39.0 μg/m³ to 100.6 μg/m³. For each 10 μg/m³ increment in PM_2.5, the hazard ratio (HR) was 1.31 (95% CI: 1.04-1.65) for stroke mortality after multivariable adjustment. In addition, the HRs of PM_2.5 decreased gradually as the increase of annual temperature range with the HRs of 1.95 (95% CI: 1.36-2.81), 1.53 (95% CI: 1.06-2.22), and 1.11 (95% CI: 0.75-1.63) in the low, middle, and high group of annual temperature range, respectively. The findings provided further evidence of long-term PM_2.5 exposure on stroke mortality in high-exposure settings such as northern China, and also highlighted the view that assessing the adverse health effects of air pollution might not ignore the role of temperature variations in the context of climate change.

Associations of Relative Humidity and Lifestyles with Metabolic Syndrome among the Ecuadorian Adult Population: Ecuador National Health and Nutrition Survey (ENSANUT-ECU) 2012

The effects of the physical environment on metabolic syndrome (MetS) are still largely unexplained. This study aimed to analyze the associations of relative humidity of residence, lifestyles, and MetS among Ecuadorian adults. Data from 6024 people aged 20 to 60 years were obtained from an Ecuador national population-based health and nutrition survey (i.e., ENSANUT-ECU, 2012) and the mean annual relative humidity (%) from the Ecuador National Institute for Meteorology and Hydrology (2012). Odds ratio (OR) with 95% confidence intervals (CI) for MetS according to groups of relative humidity were calculated using multiple logistic regression. Living in high relative humidity (>80%) increased ORs of reduced high-density lipoprotein (HDL) cholesterol (1.25; 95 % CI, 1.06–1.56) and MetS (OR = 1.20; 95 % CI,1.01–1.42) in women. Furthermore, physically active men living in high relative humidity showed lower OR of elevated triglycerides (0.56; 95 % CI,0.37–0.85) while menopausal women living in high relative humidity showed increased ORs of MetS (5.42; 95 % CI, 1.92–15.27), elevated blood pressure (3.10; 95 % CI, 1.15–8.35), and increased waist circumference (OR = 1.34; 95 % CI, 1.09–1.63). Our results show that residence in high relative humidity and menopausal status increase ORs of MetS and its components in Ecuadorian women; however, physical activity significantly reduces the OR of elevated triglycerides in men. The obtained findings may help make public health policies regarding environmental humidity management, nutritional education, menopausal care, and physical activity promotion to prevent the onset of MetS among Ecuadorian adults.

Resting Energy Expenditure and Body Composition in Overweight Men and Women Living in a Temperate Climate

This study aimed to determine whether the measured resting energy expenditure (REE) in overweight and obese patients living in a temperate climate is lower than the predicted REE; and to ascertain which equation should be used in patients living in a temperate climate. REE (indirect calorimetry) and body composition (DXA) were measured in 174 patients (88 men and 86 women; 20-68 years old) with overweight or obesity (BMI 27-45 kg m^-2). All volunteers were residents in Gran Canaria (monthly temperatures: 18-24 °C). REE was lower than predicted by most equations in our population. Age and BMI were similar in both sexes. In the whole population, the equations of Mifflin, Henry and Rees, Livingston and Owen, had similar levels of accuracy (non-significant bias of 0.7%, 1.1%, 0.6%, and -2.2%, respectively). The best equation to predict resting energy expenditure in overweight and moderately obese men and women living in a temperate climate all year round is the Mifflin equation. In men, the equations by Henry and Rees, Livingston, and by Owen had predictive accuracies comparable to that of Mifflin. The body composition-based equation of Johnston was slightly more accurate than Mifflin's in men. In women, none of the body composition-based equations outperformed Mifflin's.

Air pollution, noise exposure, and metabolic syndrome - A cohort study in elderly Mexican-Americans in Sacramento area

BACKGROUND

Previous studies suggested that air pollutants may increase the incidence of metabolic syndrome, but the potential impact from traffic sources is not well-understood. This study aimed to investigate associations between traffic-related nitrogen oxides (NOx) or noise pollution and risk of incident metabolic syndrome and its components in an elderly Mexican-American population.

METHODS

A total of 1,554 Mexican-American participants of the Sacramento Area Latino Study on Aging (SALSA) cohort were followed from 1998 to 2007. We used anthropometric measures and biomarkers to define metabolic syndrome according to the recommendations of the Third Adult Treatment Panel of the National Cholesterol Education Program (NCEP ATP III). Based on participants' residential addresses at baseline, estimates of local traffic-related NOx were generated using the California Line Source Dispersion Model version 4 (CALINE4), and of noise employing the SoundPLAN software package. We used Cox regression models with calendar time as the underlying time scale to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for associations of air pollution or noise with metabolic syndrome or its components.

RESULTS

Each per unit increase of traffic-related NOx (2.29 parts per billion (ppb)) was associated with a 15% (HR = 1.15, 95% CI: 1.04-1.28) lower level of high-density lipoprotein cholesterol (HDL-cholesterol), and each 11.6 decibels (dB) increase in noise increased the risk of developing metabolic syndrome by 17% (HR = 1.17, 95% CI: 1.01-1.35).

CONCLUSION

Policies aiming to reduce traffic-related air pollution and noise might mitigate the risk of metabolic syndrome and its components in vulnerable populations.

Ambient temperature and prevalence of diabetes and insulin resistance in the Spanish population: Di@bet.es study

Objective The activity of brown adipose tissue is sensitive to changes in ambient temperature. A lower exposure to cold could result in an increased risk of developing diabetes at population level, although this factor has not yet been sufficiently studied. Design We studied 5072 subjects, participants in a national, cross-sectional population-based study representative of the Spanish adult population (Di@bet.es study). All subjects underwent a clinical, demographic and lifestyle survey, a physical examination and blood sampling (75 g oral glucose tolerance test). Insulin resistance was estimated with the homeostasis model assessment (HOMA-IR). The mean annual temperature (°C) in each individual municipality was collected from the Spanish National Meteorology Agency. Results Linear regression analysis showed a significant positive association between mean annual temperature and fasting plasma glucose (β: 0.087, P < 0.001), 2 h plasma glucose (β: 0.049, P = 0.008) and HOMA-IR (β: 0.046, P = 0.008) in multivariate adjusted models. Logistic regression analyses controlled by multiple socio-demographic variables, lifestyle, adiposity (BMI) and geographical elevation showed increasing odds ratios for prediabetes (WHO 1999), ORs 1, 1.26 (0.95-1.66), 1.08 (0.81-1.44) and 1.37 (1.01-1.85) P for trend = 0.086, diabetes (WHO 1999) ORs 1, 1.05 (0.79-1.39), 1.20 (0.91-1.59) and 1.39 (1.02-1.90) P = 0.037, and insulin resistance (HOMA-IR ≥75th percentile of the non-diabetic population): ORs 1, 1.03 (0.82-1.30), 1.22 (0.96-1.55), 1.26 (0.98-1.63) (P for trend = 0.046) as the mean annual temperature (into quartiles) rose. Conclusions Our study reports an association between ambient temperature and the prevalence of dysglycemia and insulin resistance in Spanish adults, consistent with the hypothesis that a lower exposure to cold could be associated with a higher risk of metabolic derangements.

Inverse Association Between Metabolic Syndrome and Altitude: A Cross-Sectional Study in an Adult Population of Ecuador

Background: Metabolic syndrome (MetS) is characterized by the clustering of hyperglycemia, hypertension, hypertriglyceridemia, low high-density lipoprotein cholesterol levels and central adiposity. Altitude has been proposed as a protective factor to prevent the development of MetS and its components. Aim: To determine whether living at geographical elevation is associated with MetS and its individual components after adjustment for potential confounders in an Ecuadoran population. Methods: The study included 260 Ecuadoran university graduates over 20 years of age, from the coastal or the Andean Altiplano region. The altitude of residence was imputed with the postal code of each participant residence according to the data of the Ecuadoran Geophysical Institute of the National Polytechnic School. MetS was defined according to the harmonizing definition. Logistic regression models were fitted to assess the relationship between altitude level and the prevalence of MetS and its individual components. To test the internal validity, re-sampling techniques were used (1,000 bootstrap samples). Results: Living at high altitude was associated with less hypercholesterolemia (OR = 0.24; p < 0.001), hyperglycemia (OR = 0.25; p < 0.05) and MetS (OR = 0.24; p < 0.05), after adjusting for potential confounders. At high altitude the bootstrapped logistic regression models showed lower prevalence of hypercholesterolemia (OR = 0.30; p < 0.05), hyperglycemia (OR = 0.22; p < 0.001) and MetS (OR = 0.28; p < 0.05). The MetS score (0-5 points) showed a reduction in the number of MetS components at high altitude compared to sea level (B = -0.34; p = 0.002). A statistically significant lower self-reported energy intake was found in high altitude compared to sea level after adjustment for potential confounders (p < 0.001). Conclusion: In the present study concerning a small Ecuadoran population composed of highly educated adults living at the coast and the Andean Altiplano, living at high altitude (2,758-2,787 m) was associated with a lower prevalence of MetS, hypercholesterolemia and hyperglycemia, compared to the participants at sea level (4-6 m). In addition, an inverse association between altitude and self-reported energy intake was found after adjusting for covariates, suggesting a physiological role of appetite at high altitude even in acclimated subjects.

Cold-induced epigenetic programming of the sperm enhances brown adipose tissue activity in the offspring

Recent research has focused on environmental effects that control tissue functionality and systemic metabolism. However, whether such stimuli affect human thermogenesis and body mass index (BMI) has not been explored. Here we show retrospectively that the presence of brown adipose tissue (BAT) and the season of conception are linked to BMI in humans. In mice, we demonstrate that cold exposure (CE) of males, but not females, before mating results in improved systemic metabolism and protection from diet-induced obesity of the male offspring. Integrated analyses of the DNA methylome and RNA sequencing of the sperm from male mice revealed several clusters of co-regulated differentially methylated regions (DMRs) and differentially expressed genes (DEGs), suggesting that the improved metabolic health of the offspring was due to enhanced BAT formation and increased neurogenesis. The conclusions are supported by cell-autonomous studies in the offspring that demonstrate an enhanced capacity to form mature active brown adipocytes, improved neuronal density and more norepinephrine release in BAT in response to cold stimulation. Taken together, our results indicate that in humans and in mice, seasonal or experimental CE induces an epigenetic programming of the sperm such that the offspring harbor hyperactive BAT and an improved adaptation to overnutrition and hypothermia.

Longer-Term Outdoor Temperatures and Health Effects: A Review

PURPOSE OF REVIEW

Our goal was to assess current literature and knowledge on associations between characteristics (mean, variability, extremes) of ambient temperatures and human health. We were motivated by concerns that climate change, which operates on a time frame of decades or longer, may influence not only shorter-term associations between weather and health (daily/weekly) but also have enduring implications for population health. We reviewed papers published between 2010 and 2017 on the health effects of longer-term (3 weeks to years) exposures to ambient temperature. We sought to answer: 'What health outcomes have been associated with longer-term exposures?' We included studies on a diverse range of health outcomes, with the exception of vector borne diseases such as malaria. Longer-term exposures were considered to be exposures to annual and seasonal temperatures and temperature variability.

RECENT FINDINGS

We found 26 papers meeting inclusion criteria, which addressed mortality, morbidity, respiratory disease, obesity, suicide, infectious diseases and allergies among various age groups. In general, most studies found associations between longer-term temperature metrics and health outcomes. Effects varied by population subgroup. For example, associations with suicide differed by sex and underlying chronic illness modified effects of heat on mortality among the elderly.

SUMMARY

We found that regional and local temperatures, and changing conditions in weather due to climate change, were associated with a diversity of health outcomes through multiple mechanisms. Future research should focus on evidence for particular mechanistic pathways in order to inform adaptation responses to climate change.

Living at a Geographically Higher Elevation Is Associated with Lower Risk of Metabolic Syndrome: Prospective Analysis of the SUN Cohort

Living in a geographically higher altitude affects oxygen availability. The possible connection between environmental factors and the development of metabolic syndrome (MetS) feature is not fully understood, being the available epidemiological evidence still very limited. The aim of the present study was to evaluate the longitudinal association between altitude and incidence of MetS and each of its components in a prospective Spanish cohort, The Seguimiento Universidad de Navarra (SUN) project. Our study included 6860 highly educated subjects (university graduates) free from any MetS criteria at baseline. The altitude of residence was imputed with the postal code of each individual subject residence according to the data of the Spanish National Cartographic Institute and participants were categorized into tertiles. MetS was defined according to the harmonized definition. Cox proportional hazards models were used to assess the association between the altitude of residence and the risk of MetS during follow-up. After a median follow-up period of 10 years, 462 incident cases of MetS were identified. When adjusting for potential confounders, subjects in the highest category of altitude (>456 m) exhibited a significantly lower risk of developing MetS compared to those in the lowest tertile (<122 m) of altitude of residence [Model 2: Hazard ratio = 0.75 (95% Confidence interval: 0.58–0.97); p for trend = 0.029]. Living at geographically higher altitude was associated with a lower risk of developing MetS in the SUN project. Our findings suggest that geographical elevation may be an important factor linked to metabolic diseases.

Ambient Fine Particulate Matter, Outdoor Temperature, and Risk of Metabolic Syndrome

Ambient air pollution and temperature have been linked with cardiovascular morbidity and mortality. Metabolic syndrome and its components-abdominal obesity, elevated fasting blood glucose concentration, low high-density lipoprotein cholesterol concentration, hypertension, and hypertriglyceridemia-predict cardiovascular disease, but the environmental causes are understudied. In this study, we prospectively examined the long-term associations of air pollution, defined as particulate matter with an aerodynamic diameter less than or equal to 2.5 µm (PM_2.5), and temperature with the development of metabolic syndrome and its components. Using covariate-adjustment Cox proportional hazards models, we estimated associations of mean annual PM_2.5 concentration and temperature with risk of incident metabolic dysfunctions between 1993 and 2011 in 587 elderly (mean = 70 (standard deviation, 7) years of age) male participants in the Normative Aging Study. A 1-μg/m³ increase in mean annual PM_2.5 concentration was associated with a higher risk of developing metabolic syndrome (hazard ratio (HR) = 1.27, 95% confidence interval (CI): 1.06, 1.52), an elevated fasting blood glucose level (HR = 1.20, 95% CI: 1.03, 1.39), and hypertriglyceridemia (HR = 1.14, 95% CI: 1.00, 1.30). Our findings for metabolic syndrome and high fasting blood glucose remained significant for PM_2.5 levels below the Environmental Protection Agency's health-safety limit (12 μg/m³). A 1°C increase in mean annual temperature was associated with a higher risk of developing elevated fasting blood glucose (HR = 1.33, 95% CI: 1.14, 1.56). Men living in neighborhoods with worse air quality-with higher PM_2.5 levels and/or temperatures than average-showed increased risk of developing metabolic dysfunctions.

Oxidative Priority, Meal Frequency, and the Energy Economy of Food and Activity: Implications for Longevity, Obesity, and Cardiometabolic Disease

In most modern societies, the relationship that many individuals have with food has fundamentally changed from previous generations. People have shifted away from viewing food as primarily sustenance, and rather now seek out foods based on pure palatability or specific nutrition. However, it is far from clear what optimal nutrition is for the general population or specific individuals. We previously described the Food Triangle as a way to organize food based on an increasing energy density paradigm, and now expand on this model to predict the impact of oxidative priority and both nutrient and fiber density in relation to caloric load. When combined with meal frequency, integrated energy expenditure, macronutrient oxidative priority, and fuel partitioning expressed by the respiratory quotient, our model also offers a novel explanation for chronic overnutrition and the cause of excess body fat accumulation. Herein, we not only review how metabolism is a dynamic process subject to many regulators that mediate the fate of ingested calories but also discuss how the Food Triangle predicts the oxidative priority of ingested foods and provides a conceptual paradigm for healthy eating supported by health and longevity research.

Type 2 diabetes, but not obesity, prevalence is positively associated with ambient temperature

Cold exposure stimulates energy expenditure and glucose disposal. If these factors play a significant role in whole body energy balance, and glucose homeostasis, it is predicted that both obesity and type 2 diabetes prevalence would be lower where it is colder. Previous studies have noted connections between ambient temperature and obesity, but the direction of the effect is confused. No previous studies have explored the link of type 2 diabetes to ambient temperature. We used county level data for obesity and diabetes prevalence across the mainland USA and matched this to county level ambient temperature data. Average ambient temperature explained 5.7% of the spatial variation in obesity and 29.6% of the spatial variation in type 2 diabetes prevalence. Correcting the type 2 diabetes data for the effect of obesity reduced the explained variation to 26.8%. Even when correcting for obesity, poverty and race, ambient temperature explained 12.4% of the variation in the prevalence of type 2 diabetes, and this significant effect remained when latitude was entered into the model as a predictor. When obesity prevalence was corrected for poverty and race the significant effect of temperature disappeared. Enhancing energy expenditure by cold exposure will likely not impact obesity significantly, but may be useful to combat type 2 diabetes.

The effects of indoor and outdoor temperature on metabolic rate and adipose tissue - the Mississippi perspective on the obesity epidemic

Global warming, primarily caused by emissions of too much carbon dioxide, and climate change is a reality. This will lead to more extreme weather events with heatwaves and flooding. Some studies propose an association between thermal exposures and the prevalence of obesity with an increasing trend towards time spent in the thermal comfort zone. Longterm exposure to the thermal comfort zone can lead to a reduction of brown adipose tissue activity with an impact on energy expenditure and thermogenesis. Reduced seasonal cold exposure in combination with reduced diet-induced thermogenesis by a highly palatable high-fat and high-sugar diet and reduced physical activity contribute to the prevalence of obesity and the metabolic syndrome.

Ambient Temperature and Prevalence of Obesity: A Nationwide Population-Based Study in Korea

Background

Recent studies have suggested a possible association between outdoor or indoor temperature and obesity. We aimed to examine whether ambient temperature is associated with the prevalence of obesity or abdominal obesity in the Korean population.

Methods

Data on anthropometric, socio-demographic, laboratory and lifestyle factors were retrieved from National Health Insurance System data obtained in 2009–2010. Thirty years (1981 to 2010) of meteorological parameters for 71 observation areas were acquired from the Korea Meteorological Administration. Included in this analysis were 124,354 individuals. A body mass index (BMI) ≥ 25 kg/m² and a waist circumference (WC) ≥ 90 cm (men) or 85 cm (women) were considered to represent obesity and abdominal obesity, respectively.

Results

The mean annual temperature (MAT) ranged from 6.6°C to 16.6°C, and BMI was positively correlated with MAT (r = 0.0078, P = 0.0065). WC was positively correlated with MAT (r = 0.0165, P < 0.0001) and negatively correlated with the number of days with mean temperature < 0°C (DMT0; r = –0.0129, P = 0.0002). After adjusting for age, sex, smoking status, alcohol consumption, exercise, income, residential area and altitude, the odds ratios (95% CI) for obesity and abdominal obesity in the highest quintile MAT group were 1.045 (1.010, 1.081) and 1.082 (1.042, 1.124), respectively, compared with the lower four quintiles of the MAT group. Similarly, subjects in the area of the lowest quintile of DMT0 had significantly higher odds of abdominal obesity compared with the higher four quintile groups of DMT0.

Conclusion

This study finds an association between ambient temperature and prevalence of obesity in the Korean population when controlling for several confounding factors. Adaptive thermogenesis might be a possible explanation for this phenomenon.