Effects of light transitions on measures of alertness, arousal and comfort.

Knowledge on the onset, persistence, and symmetry of effects of lighting transitions on humans is relevant when designing dynamic lighting scenarios and, additionally, can shed light on the dominance of underlying mechanisms. We examined temporal trajectories in measures of alertness, arousal and comfort after abrupt lighting transitions that were created using two strongly contrasting light conditions (warm, dim lighting vs. cool, bright lighting). In this controlled within-subjects experiment, thirtyeight healthy subjects participated in four separate sessions of 90 min. Subjective experiences (alertness, comfort and mood) and objective measures of vigilance (PVT performance), arousal (HR, HRV, SCL), and thermoregulation (skin temperature and DPG) were studied. The comparison of the temporal trajectories following the transition in light for the different variables indicates a complex interplay of underlying physiological and psychological processes driving these effects.

Exploring the human thermoneutral zone - A dynamic approach.

To date, the position and shape of the human thermoneutral zone (TNZ) remain uncertain. Indications exist that the individual TNZ might be influenced by age, body composition and level of acclimatisation. The objective of the present study was to explore the individual metabolic TNZ, using dynamic thermal conditions to assess both metabolic lower and upper critical temperatures (LCT and UCT) and, secondly, to test the effect of passive mild heat acclimation on the human metabolic TNZ. A dynamic protocol consisting of two experimental conditions was designed: starting from a thermoneutral condition (28.8 ±â€¯0.3 °C), temperature gradually increased to 37.5 ±â€¯0.6 °C during warming (UP) or decreased to 17.8 ±â€¯0.6 °C during cooling (DOWN). For six participants, temperature increased further to 41.6 ±â€¯1.0 °C during UP. Eleven healthy men (19-31 y) underwent UP and DOWN twice, i.e. before and after passive mild heat acclimation (PMHA, 7 days at ~33 °C for 6 h/day). Energy expenditure, body temperatures and heart rate were measured during UP and DOWN. We show that the generally assumed LCT of approximately 28 °C for an average male person does not match the dynamically assessed LCTs in this study, as those were considerably lower in most cases (23.3 ±â€¯3.2 °C pre-acclimation; 23.4 ±â€¯2.0 °C post-acclimation). Distinct inter-individual variation of the dynamic LCT was evident (range pre-PMHA:9.7 °C; post-PMHA:5.4 °C). Regarding the metabolic response to increasing temperatures, only minor or no increases in energy metabolism occurred. PMHA did not significantly change the positioning of the LCTs, but lowered Tcore (pre-PMHA: -0.13 ±â€¯0.13 °C, P = 0.011; post-PMHA: -0.14 ±â€¯0.15 °C, P = 0.026) and affected skin temperature distribution. The applied method allowed for the determination of individual dynamic LCTs, however, distinct metabolic UCTs were not evident in humans. For a better understanding of the human UCT, future studies should incorporate individualised temperature ranges and also a measurement of evaporative heat loss, to allow for a two-factor analysis of both metabolic and evaporative human UCT.

Modulation of thermogenesis and metabolic health: a built environment perspective.

Lifestyle interventions, obviating the increasing prevalence of the metabolic syndrome, generally focus on nutrition and physical activity. Environmental factors are hardly covered. Because we spend on average more that 90% of our time indoors, it is, however, relevant to address these factors. In the built environment, the attention has been limited to the (assessment and optimization of) building performance and occupant thermal comfort for a long time. Only recently well-being and health of building occupants are also considered to some extent, but actual metabolic health aspects are not generally covered. In this review, we draw attention to the potential of the commonly neglected lifestyle factor 'indoor environment'. More specifically, we review current knowledge and the developments of new insights into the effects of ambient temperature, light and the interaction of the two on metabolic health. The literature shows that the effects of indoor environmental factors are important additional factors for a healthy lifestyle and have an impact on metabolic health.

Thermophysiological adaptations to passive mild heat acclimation.

Passive mild heat acclimation (PMHA) reflects realistic temperature challenges encountered in everyday life. Active heat acclimation, combining heat exposure and exercise, influences several important thermophysiological parameters; for example, it decreases core temperature and enhances heat exchange via the skin. However, it is unclear whether PMHA elicits comparable adaptations. Therefore, this study investigated the effect of PMHA on thermophysiological parameters. Participants were exposed to slightly increased temperatures (∼33°C/22% RH) for 6 h/d over 7 consecutive days. To study physiologic responses before and after PMHA, participants underwent a temperature ramp (UP), where ambient temperature increased from a thermoneutral value (28.8 ± 0.3°C) to 37.5 ± 0.6°C. During UP, core and skin temperature, water loss, cardiovascular parameters, skin blood flow and energy expenditure were measured. Three intervals were selected to compare data before and after PMHA: baseline (minutes 30-55: 28.44 ± 0.21°C), T1 (minutes 105-115: 33.29 ± 0.4°C) and T2 (minutes 130-140: 35.68 ± 0.61°C). After 7 d of PMHA, core (T1: -0.13 ± 0.13°C, P = 0.011; T2: -0.14 ± 0.15°C, P = 0.026) and proximal skin temperature (T1: -0.22 ± 0.29°C, P = 0.029) were lower during UP, whereas distal skin temperature was higher in a thermoneutral state (baseline: +0.74 ± 0.77°C, P = 0.009) and during UP (T1: +0.49 ± 0.76°C, P = .057 (not significant), T2:+0.51 ± 0.63°C, P = .022). Moreover, water loss was reduced (-30.5 ± 33.3 ml, P = 0.012) and both systolic (-7.7 ± 7.7 mmHg, P = 0.015) and diastolic (-4.4 ± 4.8 mmHg, P = 0.001) blood pressures were lowered in a thermoneutral state. During UP, only systolic blood pressure was decreased (T2: -6.1 ± 4.4 mmHg, P = 0.003). Skin blood flow was significantly decreased at T1 (-28.35 ± 38.96%, P = 0.037), yet energy expenditure remained unchanged. In conclusion, despite the mild heat stimulus, we show that PMHA induces distinct thermophysiological adaptations leading to increased resilience to heat.

The influence of light on thermal responses.

Light is essential for vision and plays an important role in non-visual responses, thus affecting alertness, mood and circadian rhythms. Furthermore, light influences physiological processes, such as thermoregulation, and therefore may be expected to play a role in thermal comfort (TC) as well. A systematic literature search was performed for human studies exploring the relation between ocular light exposure, thermophysiology and TC. Experimental results show that light in the evening can reduce melatonin secretion, delay the natural decline in core body temperature (CBT) and slow down the increase in distal skin temperature. In the morning though, bright light can result in a faster decline in melatonin levels, thus enabling a faster increase in CBT. Moreover, the colour of light can affect temperature perception of the environment. Light with colour tones towards the red end of the visual spectrum leads to a warmer perception compared to more bluish light tones. It should be noted, however, that many results of light on thermal responses are inconclusive, and a theoretical framework is largely lacking. In conclusion, light is capable of evoking thermophysiological responses and visual input can alter perception of the thermal environment. Therefore, lighting conditions should be taken into consideration during thermophysiological research and in the design of indoor climates.

Low brown adipose tissue activity in endurance-trained compared with lean sedentary men.

BACKGROUND/OBJECTIVES: It has now been unequivocally demonstrated that humans possess functional brown adipose tissue (BAT) and that human BAT can be recruited upon chronic cold stimulation. Recruitment of BAT has been postulated as a potential strategy to counteract the current global obesity epidemic. Recently, it was shown in rodents that endurance exercise training could stimulate the recruitment of brown-like adipocytes within white adipose tissue (WAT) via exercise-induced myokines such as irisin (the cleaved circulating product of the type 1 membrane protein FNDC5) and interleukin-6 (IL-6). Our objective was to test whether endurance-trained athletes had increased cold-stimulated BAT activity and browning of subcutaneous WAT compared with lean sedentary males. SUBJECTS/METHODS: Twelve endurance-trained athletes and 12 lean sedentary males were measured during 2 h of mild cold exposure to determine cold-induced BAT activity via [(18)F]fluorodeoxyglucose-positron emission tomography-computed tomography ([(18)F]FDG-PET-CT) scanning. Skeletal muscle FNDC5 expression, as well as plasma irisin and IL-6 levels were determined. In addition, a subcutaneous abdominal WAT biopsy was taken to measure gene expression of several markers for browning of WAT. RESULTS: Cold-induced BAT activity was significantly lower in athletes, and no differences in gene expression of classical brown and beige adipocyte markers were detected in subcutaneous WAT between the groups. As expected, mRNA expression of FNDC5 in skeletal muscle was significantly higher in endurance athletes but plasma irisin and Il-6 levels were similar in both groups. CONCLUSIONS: These results indicate that chronic endurance exercise is not associated with brown and beige adipocyte recruitment; in fact endurance training appears to be linked to lower the metabolic activity of BAT in humans.

Incorporating neurophysiological concepts in mathematical thermoregulation models.

Skin blood flow (SBF) is a key player in human thermoregulation during mild thermal challenges. Various numerical models of SBF regulation exist. However, none explicitly incorporates the neurophysiology of thermal reception. This study tested a new SBF model that is in line with experimental data on thermal reception and the neurophysiological pathways involved in thermoregulatory SBF control. Additionally, a numerical thermoregulation model was used as a platform to test the function of the neurophysiological SBF model for skin temperature simulation. The prediction-error of the SBF-model was quantified by root-mean-squared-residual (RMSR) between simulations and experimental measurement data. Measurement data consisted of SBF (abdomen, forearm, hand), core and skin temperature recordings of young males during three transient thermal challenges (1 development and 2 validation). Additionally, ThermoSEM, a thermoregulation model, was used to simulate body temperatures using the new neurophysiological SBF-model. The RMSR between simulated and measured mean skin temperature was used to validate the model. The neurophysiological model predicted SBF with an accuracy of RMSR < 0.27. Tskin simulation results were within 0.37 °C of the measured mean skin temperature. This study shows that (1) thermal reception and neurophysiological pathways involved in thermoregulatory SBF control can be captured in a mathematical model, and (2) human thermoregulation models can be equipped with SBF control functions that are based on neurophysiology without loss of performance. The neurophysiological approach in modelling thermoregulation is favourable over engineering approaches because it is more in line with the underlying physiology.

The influence of local effects on thermal sensation under non-uniform environmental conditions--gender differences in thermophysiology, thermal comfort and productivity during convective and radiant cooling.

Applying high temperature cooling concepts, i.e. high temperature cooling (T(supply) is 16-20°C) HVAC systems, in the built environment allows the reduction in the use of (high quality) energy. However, application of high temperature cooling systems can result in whole body and local discomfort of the occupants. Non-uniform thermal conditions, which may occur due to application of high temperature cooling systems, can be responsible for discomfort. Contradictions in literature exist regarding the validity of the often used predicted mean vote (PMV) index for both genders, and the index is not intended for evaluating the discomfort due to non-uniform environmental conditions. In some cases, however, combinations of local and general discomfort factors, for example draught under warm conditions, may not be uncomfortable. The objective of this study was to investigate gender differences in thermophysiology, thermal comfort and productivity in response to thermal non-uniform environmental conditions. Twenty healthy subjects (10 males and 10 females, age 20-29 years) were exposed to two different experimental conditions: a convective cooling situation (CC) and a radiant cooling situation (RC). During the experiments physiological responses, thermal comfort and productivity were measured. The results show that under both experimental conditions the actual mean thermal sensation votes significantly differ from the PMV-index; the subjects are feeling colder than predicted. Furthermore, the females are more uncomfortable and dissatisfied compared to the males. For females, the local sensations and skin temperatures of the extremities have a significant influence on whole body thermal sensation and are therefore important to consider under non-uniform environmental conditions.

Increase in brown adipose tissue activity after weight loss in morbidly obese subjects.

CONTEXT: Stimulation of thermogenesis in brown adipose tissue (BAT) is a potential target to treat obesity. We earlier demonstrated that BAT activity is relatively low in obese subjects. It is unknown whether BAT can be recruited in adult humans. OBJECTIVE: To study the dynamics of BAT, we observed BAT activity in morbidly obese subjects before and after weight loss induced by bariatric surgery. DESIGN: This was an observational prospective cohort study. SETTING: The study was conducted at a referral center. PATIENTS: Ten morbidly obese subjects eligible for laparoscopic adjustable gastric banding surgery were studied before and 1 yr after bariatric surgery. MAIN OUTCOME MEASURE: The main outcome measure was BAT activity, as determined after acute cold stimulation using (18)F-fluorodeoxyglucose positron emission tomography and computed tomography. RESULTS: Before surgery, only two of 10 subjects showed active BAT. One year after surgery, the number of subjects with active BAT was increased to five. After weight loss, BAT-positive subjects had significantly higher nonshivering thermogenesis compared with BAT-negative subjects (P < 0.05). CONCLUSIONS: The results show that in humans BAT can be recruited in the regions in which it was also reported in lean subjects before. These results for the first time show recruitment of BAT in humans and may open the door for BAT-targeted treatments of obesity.

Thermal sensation: a mathematical model based on neurophysiology.

UNLABELLED: Thermal sensation has a large influence on thermal comfort, which is an important parameter for building performance. Understanding of thermal sensation may benefit from incorporating the physiology of thermal reception. The main issue is that humans do not sense temperature directly; the information is coded into neural discharge rates. This manuscript describes the development of a mathematical model of thermal sensation based on the neurophysiology of thermal reception. Experimental data from two independent studies were used to develop and validate the model. In both studies, skin and core temperature were measured. Thermal sensation votes were asked on the seven-point ASHRAE thermal sensation scale. For the development dataset, young adult males (N=12, 0.04Clo) were exposed to transient conditions; Tair 30-20-35-30°C. For validation, young adult males (N=8, 1.0Clo) were exposed to transient conditions; Tair: 17-25-17°C. The neurophysiological model significantly predicted thermal sensation for the development dataset (r2=0.89, P<0.001). Only information from warm-sensitive skin and core thermoreceptors was required. Validation revealed that the model predicted thermal sensation within acceptable range (root mean squared residual=0.38). The neurophysiological model captured the dynamics of thermal sensation. Therefore, the neurophysiological model of thermal sensation can be of great value in the design of high-performance buildings. PRACTICAL IMPLICATIONS: The presented method, based on neurophysiology, can be highly beneficial for predicting thermal sensation under complex environments with respect to transient environments.

Differences between young adults and elderly in thermal comfort, productivity, and thermal physiology in response to a moderate temperature drift and a steady-state condition.

UNLABELLED: Results from naturally ventilated buildings show that allowing the indoor temperature to drift does not necessarily result in thermal discomfort and may allow for a reduction in energy use. However, for stationary conditions, several studies indicate that the thermal neutral temperature and optimum thermal condition differ between young adults and elderly. There is a lack of studies that describe the effect of aging on thermal comfort and productivity during a moderate temperature drift. In this study, the effect of a moderate temperature drift on physiological responses, thermal comfort, and productivity of eight young adults (age 22-25 year) and eight older subjects (age 67-73 year) was investigated. They were exposed to two different conditions: S1-a control condition; constant temperature of 21.5 degrees C; duration: 8 h; and S2-a transient condition; temperature range: 17-25 degrees C, duration: 8 h, temperature drift: first 4 h: +2 K/h, last 4 h: -2 K/h. The results indicate that thermal sensation of the elderly was, in general, 0.5 scale units lower in comparison with their younger counterparts. Furthermore, the elderly showed more distal vasoconstriction during both conditions. Nevertheless, TS of the elderly was related to air temperature only, while TS of the younger adults also was related to skin temperature. During the constant temperature session, the elderly preferred a higher temperature in comparison with the young adults. PRACTICAL IMPLICATIONS: Because the stock of fossil fuels is limited, energy savings play an important role. Thermal comfort is one of the most important performance indicators to successfully apply measures to reduce the energy need in buildings. Allowing drifts in indoor temperature is one of the options to reduce the energy demand. This study contributes to the knowledge concerning the effects of a moderate temperature drift and the age of the inhabitants on their thermal comfort.

Cold-induced vasoconstriction at forearm and hand skin sites: the effect of age.

During mild cold exposure, elderly are at risk of hypothermia. In humans, glabrous skin at the hands is well adapted as a heat exchanger. Evidence exists that elderly show equal vasoconstriction due to local cooling at the ventral forearm, yet no age effects on vasoconstriction at hand skin have been studied. Here, we tested the hypotheses that at hand sites (a) elderly show equal vasoconstriction due to local cooling and (b) elderly show reduced response to noradrenergic stimuli. Skin perfusion and mean arterial pressure were measured in 16 young adults (Y: 18-28 years) and 16 elderly (E: 68-78 years). To study the effect of local vasoconstriction mechanisms local sympathetic nerve terminals were blocked by bretylium (BR). Baseline local skin temperature was clamped at 33 degrees C. Next, local temperature was reduced to 24 degrees C. After 15 min of local cooling, noradrenaline (NA) was administered to study the effect of neural vasoconstriction mechanisms. No significant age effect was observed in vasoconstriction due to local cooling at BR sites. After NA, vasoconstriction at the forearm showed a significant age effect; however, no significant age effect was found at the hand sites. [Change in CVC (% from baseline): Forearm Y: -76 +/- 3 vs. E: -60 +/- 5 (P < 0.01), dorsal hand Y: -74 +/- 4 vs. E: -72 +/- 4 (n.s.), ventral hand Y: -80 +/- 7 vs. E: -70 +/- 11 (n.s.)]. In conclusion, in contrast to results from the ventral forearm, elderly did not show a blunted response to local cooling and noradrenaline at hand skin sites. This indicates that at hand skin the noradrenergic mechanism of vasoconstriction is maintained with age.

Recent advances in adaptive thermogenesis: potential implications for the treatment of obesity.

Large inter-individual differences in cold-induced (non-shivering) and diet-induced adaptive thermogenesis exist in animals and humans. These differences in energy expenditure can have a large impact on long-term energy balance and thus body weight (when other factors remain stable). Therefore, the level of adaptive thermogenesis might relate to the susceptibility to obesity; efforts to increase adaptive thermogenesis might be used to treat obesity. In small mammals, the main process involved is mitochondrial uncoupling in brown adipose tissue (BAT), which is regulated by the sympathetic nervous system. For a long time, it was assumed that mitochondrial uncoupling is not a major physiological contributor to adaptive thermogenesis in adult humans. However, several studies conducted in recent years suggest that mitochondrial uncoupling in BAT and skeletal muscle tissue in adult humans can be physiologically significant. Other mechanisms besides mitochondrial uncoupling that might be involved are futile calcium cycling, protein turnover and substrate cycling. In conjunction with recent advances on signal transduction studies, this knowledge makes manipulation of adaptive thermogenesis a more realistic option and thus a pharmacologically interesting target to treat obesity.

Hypoxia induces no change in cutaneous thresholds for warmth and cold sensation.

Hypoxia can affect perception of temperature stimuli by impeding thermoregulation at a neural level. Whether this impact on the thermoregulatory response is solely due to affected thermoregulation is not clear, since reaction time may also be affected by hypoxia. Therefore, we studied the effect of hypoxia on thermal perception thresholds for warmth and cold. Thermal perception thresholds were determined in 11 healthy overweight adult males using two methods for small nerve fibre functioning: a reaction-time inclusive method of limits (MLI) and a reaction time exclusive method of levels (MLE). The subjects were measured under normoxic and hypoxic conditions using a cross-over design. Before the thermal threshold tests under hypoxic conditions were conducted, the subjects were acclimatized by staying 14 days overnight (8 h) in a hypoxic tent system (Colorado Altitude Training: 4,000 m). For normoxic measurements the same subjects were not acclimatized, but were used to sleep in the same tent system. Measurements were performed in the early morning in the tent. Normoxic MLI cold sensation threshold decreased significantly from 30.3 +/- 0.4 (mean +/- SD) to 29.9 +/- 0.7 degrees C when exposed to hypoxia (P < 0.05). Similarly, mean normoxic MLI warm sensation threshold increased from 34.0 +/- 0.9 to 34.5 +/- 1.1 degrees C (P < 0.05). MLE measured threshold for cutaneous cold sensation was 31.4 +/- 0.4 and 31.2 +/- 0.9 degrees C under respectively normoxic and hypoxic conditions (P > 0.05). Neither was there a significant change in MLE warm threshold comparing normoxic (32.8 +/- 0.9 degrees C) with hypoxic condition (32.9 +/- 1.0 degrees C) (P > 0.05). Exposure to normobaric hypoxia induces slowing of neural activity in the sensor-to-effector pathway and does not affect cutaneous sensation threshold for either warmth or cold detection.

A model to predict patient temperature during cardiac surgery.

A core temperature drop after cardiac surgery slows down the patient's recuperation process. In order to minimize the amount of the so-called afterdrop, more knowledge is needed about the impaired thermoregulatory system during anesthesia and the effect of different protocols on temperature distribution. Therefore, a computer model has been developed that describes heat transfer during cardiac surgery. The model consists of three parts: (1) a passive part, which gives a simplified description of the human geometry and the passive heat transfer processes, (2) an active part that takes into account the thermoregulatory system as a function of the amount of anesthesia and (3) submodels, through which it is possible to adjust the boundary conditions. The validity of the new model was tested by comparing the model results to the measurement results of three surgical procedures. A good resemblance was found between simulation results and the experiments. Next, a model application was shown. A parameter study was performed to study the effect of different temperature protocols on afterdrop. It was shown that the effectiveness of forced-air heating is larger than the benefits resulting from increased environmental temperature or usage of a circulating water mattress. Ultimately, the model could be used to develop a monitoring decision system that advises clinicians what temperature protocol will be best for the patient.

Assessment of body composition and breast milk volume in lactating mothers in pastoral communities in Pokot, Kenya, using deuterium oxide.

BACKGROUND: In sub-Saharan Africa, the practice of breast-feeding infants is common. Records documenting the intake of breast milk amongst infants are limited. This study evaluated the association between maternal body composition and the intake of breast milk in infants from the pastoral communities within Pokot, Kenya. METHODS: The study was conducted in 10 lactating mothers who were participating in a longitudinal study aimed at determining maternal body composition, iron stores and vitamin A status during the third trimester pregnancy and four months after they had given birth. Maternal and infant anthropometric measurements were made, and maternal blood samples were taken to determine serum retinol and ferritin levels. Infant milk intake and maternal fat-free mass (FFM) and percent body fat (% BF) were measured using 'the dose to the mother method'. A measured deuterium oxide ((2)H(2)O) dose was given to the mother. Urine and breast milk from the mother, and saliva samples from the infant, were collected on days 1, 8 and 14 after dosing. RESULTS: The mean (+/- SD) maternal mid upper arm circumference (MUAC) and body mass index (BMI) were 21.8 (0.9) cm and 18.6 (1.0) kg/height (m(2)), respectively. Infant weight and weight/age Z score were 4.956 (0.874) kg and -1.750 (0.77), respectively. Throughout the study, the infants gained 20 (4) g/day in body weight and had a milk intake of 555 (22) ml/day. The energy intake of the infant was 1,602 (148) kJ/day and was lower (p < 0.05) than the 2,404 (423) kJ/day estimated requirement by the FAO/WHO/UNU. The maternal FFM, %BF, Hb, Hct, ferritin and retinol were 32.8 (3.1) kg, 17.24 (7.0), 11.5 (1.3) g/dl, 33.9 (4.9), 16.2 (0.1) microg/l and 0.894 (0.16) micromol/l, respectively. Infant milk intake was significantly and positively correlated to maternal pregnancy triceps (r = 0.679) p < 0.05) and pregnancy MUAC (r = 0.725) p < 0.05). Maternal pregnancy MUAC was an important predictor of infant breast milk intake. CONCLUSION: Data on volume of breast milk consumed by the infants suggests, at least for this group of infants, that adequate growth may not be achieved. There is a possibility that lactating mothers practicing exclusive breast-feeding and living under harsh conditions may experience periods of low breast milk volume. Body composition and biochemical findings among this group of Pokot mothers indicate dietary inadequacies that require nutritional intervention.

Seasonal changes in metabolic and temperature responses to cold air in humans.

The metabolic and temperature response to mild cold were investigated in summer and winter in a moderate oceanic climate. Subjects were 10 women and 10 men, aged 19-36 years and BMI 17-32 kg/m2. Metabolic rate (MR) and body temperatures were measured continuously in a climate chamber with an ambient temperature of 22 degrees C for 1 h and subsequently 3 h of 15 degrees C. The average metabolic response during cold exposure, measured as the increase in kJ/min over time, was significantly higher in winter (11.5%) compared to summer (7.0%, P < .05). The temperature response was comparable in both seasons. The metabolic response in winter was significantly related to the response in summer (r2 = .47, P < .001). Total heat production during cold exposure was inversely related to the temperature response in both seasons (summer, r2 = .39, P < .01; winter r2 = .32, P < .05). In conclusion, the observed higher metabolic response in winter compared to summer indicates cold adaptation. The magnitude of the cold response varies, but the relative contribution of metabolic and temperature response was subject specific and consistent throughout the seasons, which can have implications for energy balance and body composition.

Serum retinol, iron status and body composition of lactating women in Nandi, Kenya.

BACKGROUND: Maternal vitamin A and iron status was investigated among lactating mothers in a rural community in Kenya. The aim of the study was to establish the prevalence and the relationship of these key nutrients to maternal body composition. METHODS: Eighty-eight mothers provided samples of breast milk and blood for determination of breast milk vitamin A, serum retinol and ferritin. Estimators of body composition were based on the mother's weight, height and skinfold measurements. RESULTS: A total of 78.1% women had breast milk retinol <1.05 micromol/l with 38 and 62% having lactated for a period of <4 and >4 months, respectively. Prevalence of severely deficient serum retinol <0.35 micromol/l and ferritin <12 microg/l was 10 and 37%, respectively. Women with serum ferritin <12 microg/l had significantly lower average hemoglobin (p < 0.01), hematocrit (p < 0.01) and serum retinol (p < 0.05). Serum retinol of mothers who had lactated for <4 months was significantly but negatively correlated with total body fat (r = -0.40; p < 0.05). With a lactation period of >4 months a close relationship was found between serum retinol and hemoglobin (r = 0.26; p <0.01), serum retinol and serum ferritin (r = 0.20; p < 0.05), and fat free mass significantly but negatively correlated with breast milk fat (r = -0.27; p < 0.05). Serum retinol in combination with hematocrit significantly affected both maternal hemoglobin (p < 0.01) and serum ferritin (p < 0.01). CONCLUSION: A high prevalence of vitamin A and iron deficiency was observed in this group of lactating women. Low levels of fat mass were directly related to these indicators of malnutrition.

The effect of mild cold exposure on UCP3 mRNA expression and UCP3 protein content in humans.

OBJECTIVE: In rodents, adaptive thermogenesis in response to cold exposure and high-fat feeding is accomplished by the activation of the brown adipose tissue specific mitochondrial uncoupling protein, UCP1. The recently discovered human uncoupling protein 3 is a possible candidate for adaptive thermogenesis in humans. In the present study we examined the effect of mild cold exposure on the mRNA and protein expression of UCP3. SUBJECTS: Ten healthy male volunteers (age 24.4 +/- 1.6 y; height 1.83 +/- 0.02 m; weight 77.3 +/- 3.0 kg; percentage body fat 19 +/- 2). DESIGN: Subjects stayed twice in the respiration chamber for 60 h (20.00-8.00 h); once at 22 degrees C (72 degrees F), and once at 16 degrees C (61 degrees F). After leaving the respiration chamber, muscle biopsies were taken and RT-competitive-PCR and Western blotting was used to measure UCP3 mRNA and protein expression respectively. RESULTS: Twenty-four-hour energy expenditure was significantly increased at 16 degrees C compared to 22 degrees C (P<0.05). At 16 degrees C, UCP3T (4.6 +/- 1.0 vs 7.7 +/- 1.5 amol/microg RNA, P=0.07), UCP3L (2.0 +/- 0.5 vs 3.5 +/- 0.9 amol/microg RNA, P=0.1) and UCP3S (2.6 +/- 0.6 vs 4.2 +/- 0.7 amol/microg RNA, P=0.07) mRNA expression tended to be lower compared with at 22 degrees C, whereas UCP3 protein content was, on average, not different. However, the individual differences in UCP3 protein content (16-22 degrees C) correlated positively with the differences in 24 h energy expenditure (r=0.86, P<0.05). CONCLUSION: The present study suggests that UCP3 protein content is related to energy metabolism in humans and might help in the metabolic adaptation to cold exposure. However, the down-regulation of UCP3 mRNA with mild cold exposure suggests that prolonged cold exposure will lead to lower UCP3 protein content. What the function of such down-regulation of UCP3 could be is presently unknown.

Energy metabolism in humans at a lowered ambient temperature.

OBJECTIVE: Assessment of the effect of a lowered ambient temperature, ie 16 degrees C (61 degrees F), compared to 22 degrees C (72 degrees F), on energy intake (EI), energy expenditure (EE) and respiratory quotient (RQ) in men. DESIGN: Randomized within-subject design in which subjects stayed in a respiration chamber three times for 60 h each, once at 22 degrees C, and twice at 16 degrees C, wearing standardized clothing, executing a standardized daily activities protocol, and were fed in energy balance (EBI): no significant difference between EE and EI over 24 h). During the last 24 h at 22 degrees C, and once during the last 24 h at 16 degrees C, they were fed ad libitum. SUBJECTS: Nine dietary unrestrained male subjects (ages 24+/-5 y, body mass index (BMI) 22.7+/-2.1 kg/m(2), body weight 76.2+/-9.4 kg, height 1.83+/-0.06 m, 18+/-5% body fat). RESULTS: At 16 degrees C (EB), EE (total 24 h EE) was increased to 12.9+/-2.0 MJ/day as compared to 12.2+/-2.2 MJ/day at 22 degrees C (P<0.01). The increase was due to increases in sleeping metabolic rate (SMR; the lowest EE during three consecutive hours with hardly any movements as indicated by radar): 7.6+/-0.7 vs 7.2+/-0.7 MJ/day (P<0.05) and diet-induced thermogenesis (DIT; EE-SMR, when activity induced energy expenditure as indicated by radar=0): 1.7+/-0.4 vs 1.0+/-0.4 MJ/day (P<0.01). Physical activity level (PAL; EE/SMR) was 1.63-1.68. At 16 degrees C compared to at 22 degrees C, rectal, proximal and distal skin temperatures had decreased (P<0.01). RQ was not different between the two ambient temperature situations. During ad libitum feeding, subjects overate by 32+/-12% (at 22 degrees C) and by 34+/-14% (at 16 degrees C). Under these circumstances, the decrease of rectal temperature at 16 degrees C was attenuated, and inversely related to percentage overeating (r(2)=0.7; P<0.01). CONCLUSION: We conclude that at 16 degrees C, compared to 22 degrees C, energy metabolism was increased, due to increases in SMR and DIT. Overeating under ad libitum circumstances at 16 degrees C attenuated the decrease in rectal core body temperature.