Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Takafumi Maeda Last modified date:2019.06.10

Professor / Physiological Anthropology / Department of Human Science / Faculty of Design


Papers
1. Daijiro Abe, Yoshiyuki Fukuoka, Takafumi Maeda, Masahiro Horiuchi, Energy cost and lower leg muscle activities during erect bipedal locomotion under hyperoxia, Journal of Physiological Anthropology, 10.1186/s40101-018-0177-7, 37, 18, 2018.06.
2. Takafumi Maeda, Relationship between maximum oxygen uptake and peripheral vasoconstriction in a cold environment, Journal of Physiological Anthropology, https://doi.org/10.1186/s40101-017-0158-2, 36, 42, 2017.12, Various individual characteristics affect environmental adaptability of a human. The present study evaluates the relationship between physical fitness and peripheral vasoconstriction in a cold environment.
Seven healthy male students (aged 22.0 years) participated in this study. Cold exposure tests consisted of supine rest for 60 min at 28 °C followed by 90 min at 10 °C. Rectal and skin temperatures at seven sites, oxygen consumption, and the diameter of a finger vein were measured during the experiment. Metabolic heat production, skin heat conductance, and the rate of vasoconstriction were calculated. Individual maximum oxygen consumption, a direct index of aerobic fitness, was measured on the day following the cold exposure test.
Decreases in temperature of the hand negatively correlated with the changes in rectal temperature. Maximum oxygen consumption and the rate of vasoconstriction are positively correlated. Furthermore, pairs of the following three factors are also significantly correlated: rate of metabolic heat production, skin heat conductance, and the rate of vasoconstriction.
The results of this study suggested that the capacity for peripheral vasoconstriction can be improved by physical exercise. Furthermore, when exposed to a cold environment, fitter individuals could maintain metabolic heat production at the resting metabolic level of a thermoneutral condition, as they correspondingly lost less heat..
3. Takafumi Maeda, Tetsuhito Fukushima, Keita Ishibashi, Shigekazu Higuchi, Involvement of Basal Metabolic Rate in Determination of Type of Cold Tolerance, Journal of Physiological Anthropology, http://doi.org/10.2114/jpa2.26.415, 26, 3, 415-418, 2007.07, This study aimed to assess the relationship between basal metabolic rate (BMR) and metabolic heat production, and to clarify the involvement of BMR in determining the phenotype of cold tolerance. Measurements of BMR, maximum oxygen uptake, and cold exposure test were conducted on ten males. In the cold exposure test, rectal (Trec) and mean skin temperatures (Tms), oxygen uptake, and blood flow at forearm (BFarm) were measured during exposure to cold (10°C) for 90 min. Significant correlations were observed between BMR and increasing rate of oxygen uptake, as well as between decreasing rate of BFarm and increasing rate of oxygen uptake at the end of cold exposure. These findings suggested that individuals with a lower BMR were required to increase their metabolic heat production during cold exposure, and that those with a higher BMR were able to moderate increased metabolic heat production during cold exposure because they were able to reduce heat loss. This study showed that BMR is an important factor in determining the phenotype of cold tolerance, and that individuals with a low BMR showed calorigenic-type cold adaptation, whereas subjects with a high BMR exhibited adiabatic-type cold adaptation by peripheral vasoconstriction..
4. Takafumi Maeda, Mitsuhiro Ohta, Shin-Ya Kaneko, Hideyuki Kanda, Tetsuhito Fukushima, Relationships between heatstroke symptoms and lifestyles in Japanese forestry workers, Journal of the Human-Environment System, http://doi.org/10.1618/jhes.13.1, 13, 1, 1-6, 2011.03, Several risk factors for heatstroke among forestry workers were previously reported, but the effects of lifestyles of the workers on heatstroke symptoms remain unknown. This study examines the effects of lifestyles on heatstroke symptoms among Japanese forestry workers during the summer. We distributed a questionnaire to 97 forestry workers about heatstroke symptoms, hydration, hotness in workplace, lifestyles including food consumption, sleep duration, exercise, alcohol consumption, and smoking, age, and years of forestry service, and measured physical characteristics. The total health score was used as an index of healthy habits. Thirty-seven workers (38.1%) experienced heatstroke symptoms. Heatstroke and asymptomatic groups significantly differed in terms of age, years of forestry service, frequency and volume of hydration, frequency of urination, and perceived hotness. Logistic regression analysis selected the following key variables associated with the development of heatstroke symptoms: years of forestry service, frequency of hydration adjusted by frequency of urination, and total health score. In conclusion, the present study revealed that one third of forestry workers develop some early symptoms of heatstroke during work, and healthy habits reduce the risk of heatstroke in forestry workers..
5. Takafumi Maeda, Shin-Ya Kaneko, Mitsuhiro Ohta, Kazuko Tanaka, Akihiko Sasaki, Tetsuhito Fukushima, Risk factors for heatstroke in Japanese forestry workers, Journal of Occupational Health, http://doi.org/10.1539/joh.48.223, 48, 4, 223-229, 2006.08, We examined the risk factors for heatstroke among forestry workers in Japan during the summer. We distributed a questionnaire to 124 forestry workers to determine heatstroke symptoms, degree of sweating and hydration, as well as perceived hotness and amount of sunlight at work sites. Forty of the workers (32.3%) reported experiencing heatstroke symptoms. Thirteen and 21 of them reported such symptoms during July and August, respectively. Eleven workers experienced heatstroke at around 14:00; 5 and 4 developed symptoms at around 11:00 and 10:00, respectively. Groups with and without heatstroke symptoms significantly differed in terms of perceived hotness (p<0.05), sunlight (p<0.05), degree of sweating (p<0.01) and frequency of hydration (p<0.05) while working. Heatstroke symptoms developed in 60.6% of workers aged up to 50 yr, but in only 22.0% of those over the age of 51 (p<0.01). Multiple regression analysis selected the following key variables associated with the development of heatstroke symptoms (R2=0.236 and p=0.006): frequency of urination, hotness, BMI and years of forestry work (standard coefficients: +0.229, +0.194, +0.280 and -0.162, respectively). The results of the present study showed that one third of forestry workers developed some symptoms of early heatstroke during summer forestry work. Furthermore, the results indicate that a short duration of forestry service was one of the risk factors contributing to the onset of heatstroke, in addition to heat stress, loss of body water and electrolytes, and obesity..
6. Takafumi Maeda, Akiko Sugawara, Tetsuhito Fukushima, Shigekazu Higuchi, Keita Ishibashi, Effects of Lifestyle, Body Composition, and Physical Fitness on Cold Tolerance in Humans, Journal of Physiological Anthropology and Applied Human Science, http://doi.org/10.2114/jpa.24.439, 24, 4, 439-443, 2005.08, [URL], In the present study, we attempted to clarify the effects of lifestyle and body compositions on basal metabolism and to clarify the effects of physical training on thermoregulatory responses to cold. Basal metabolism, body compositions, and questionnaires regarding lifestyle were evaluated in 37 students. From multiple linear regression analysis, sex, muscle weight, fat intake, and diurnal temperature were selected as significant explanatory variables. In a second experiment, rectal and the skin temperature at 7 different points as well as the oxygen uptake of eight males were measured at 10°C for 90 min before and after training. The decline in rectal temperature that was observed before training was not observed after training. In addition, rectal temperature was significantly higher at post-training than at pre-training. These results suggest that some lifestyle factors affect cold tolerance; in particular, daily activity might improve our ability to control heat radiation and basal heat production..
7. Takafumi Maeda, Perspectives on Environmental Adaptability and Physiological Polymorphism in Thermoregulation, Journal of Physiological Anthropology and Applied Human Science, http://doi.org/10.2114/jpa.24.237, 24, 3, 237-240, 2005.06, [URL].
8. Masatoshi Tanaka, Anne-Virginie Desruelle, Hayet Sari, Victor Candas, Kazuko Tanaka, Takafumi Maeda, Effects of decreasing air temperature on peripheral thermal reactions in males and females, Environmental Health and Preventive Medicine , http://doi.org/10.1007/BF02897912, 8, 5, 178-183, 2003.11, [URL], Objectives: This study was performed to determine the effects of decreasing ambient temperature on peripheral blood flow and body temperature of males and females in a thermal neutral zone for references to the thermal standard of office workers. Methods: Peripheral blood flows of the hand and feet, and body temperatures and so on of male and female subjects were measured in a climatic chamber. Air temperature was maintained at 28.5°C at the beginning. After this, air temperature was decreased linearly to 21.0°C over a period of 60 minutes. Finally, air temperature was maintained at 21.0°C. Results: Blood flows and skin temperatures of male and female subjects became similar or showed no significant difference at beginning and the end of the experiment. Skin blood flow of the hand and skin temperatures of the hand and fingers decreased, and these values in females were lower than in males, when air temperature was decreased linearly in a thermal neutral zone. However, there were no remarkable differences between males and females in sublingual and mean skin temperatures during the experiment. Conclusion: Minimum air temperature at the thermal standard for offices in Japan is 17°C, which may be too low to be comfortable or neutral. Even in a neutral thermal condition, it is better that office workers are provided some protection such as a blanket or clothing, to protect peripheral body parts from cooling in winter, as there are individual differences in physiological thermal reactions..
9. Shin-Ya Kaneko, Takafumi Maeda, Akihiko Sasaki, Akihiko Sato, Kazuko Tanaka, Toshio Kobayashi, Masatoshi Tanaka, Tetsuhito Fukushima, Changes in Health Habits of Female Shift Workers, Journal of Occupational Health, http://doi.org/10.1539/joh.46.192, 46, 3, 192-198, 2004.06, [URL], This paper examines the effects of shift work on the lifestyles of female factory workers. As an indicator of healthy lifestyle habits, we used a scoring system (referred to below as the ‘health score’) based on Lester Breslow’s health habits. The ‘health score’ of the women was higher than that of the men, but the shift workers’ score was lower than that of the non-shift workers (p<0.01). In addition, the score of workers who had changed from non-shift work to double-shift work was remarkably low (p<0.01). These results suggest that, while the female shift workers manage to maintain relatively healthy lifestyles in comparison with the males, they have more difficulty maintaining these habits than do female workers who do not perform shift work. It can be concluded that, in addition to heightening women’s consciousness of their own health, surrounding entities such as the work environment, the home, and the community in general need to pay due care to Japan’s female shift workers. .
10. Shin-Ya Kaneko, Takafumi Maeda, Akihiko Sasaki, Akihiko Sato, Kazuko Tanaka, Toshio Kobayashi, Masatoshi Tanaka, Tetsuhito Fukushima, Effect of Shift Work on Mental State of Factory Workers, Fukushima Journal of Medical Science, http://doi.org/10.5387/fms.50.1, 50, 1, 1-9, 2003.10, This paper examines the effects of shift work on the mental state of factory workers. As an indicator of the workers' mental condition, the authors used a scoring system (referred to below as the ‘ depression tendency score') based on the SRQ-D investigative report. The depression tendency score of the men was higher among the shift worker group than among the regular day worker group (p<0.01). The depression tendency score of the male back-to-back shift workers was higher than that of the male regular day workers among skilled workers (p<0.05). Among the women, no notable difference in depression tendency score was observed between the regular day worker group and the shift worker group. However, the depression tendency score of the female two-shift workers was higher than that of the female regular day workers among skilled workers (p<0.05). We conclude that the mental health of men is easily affected by back-to-back shift work and that of women is affected by two-shift work because of the difference in modern societal/home role between man and woman..
11. Kazuko Tanaka, Takafumi Maeda, Toshio Kobayashi, Masatoshi Tanaka, Tetsuhito Fukushima, A survey of urinary hippuric acid and subjective symptoms among occupational low toluene exposed workers, Fukushima Journal of Medical Science, http://doi.org/10.5387/fms.49.129, 49, 2, 129-139, 2003.10.
12. Akiko Sugawara, Hiroko Yokoyama, Mitsuhiro Ohta, Takafumi Maeda, Kazuko Tanaka, Tetsuhito Fukushima, The effect of heavy metals on nicotinamide N-methyltransferase activity in vitro relating to Parkinson’s disease, Environmental Health and Preventive Medicine, http://doi.org/10.1007/BF02897708, 10, 4, 180-183, 2005.07, Objective: The aims of this study were to determine the effects of heavy metals such as manganese on nicotinamideN-methyltransferase (EC 2.1.1.1) (NNMT) activity and to consider the possibility of involvement of NNMT activation in the pathogenesis of heavy metal induced Parkinson’s disease. Methods: NNMT activity in supernatants separated from brain, liver and kidney homogenates of 5 elderly male Wistar rats by centrifugation were measured by high performance liquid chromatography system with fluorescence. NNMT activity under the conditon of 0.5 or 5.0 mM Mn2+, Fe2+, Cu2+ or Cd2+ was compared with control (no metal ion existence). Results: NNMT activities in rat brain, liver and kidneys were significantly decreased by Cu2+, and those in the liver and kidneys were significantly decreased by Cd2+. Mn2+ reduced NNMT activity only in the liver. Fe2+ had no effect on NNMT activity. Conclusions: No metal increased NNMT activity in this study, contrary to our hypothesis. Further study is needed to clarify the reason why the effects of Mn2+ and Fe2+ which have a high relevance to Parkinson’s disease on NNMT activity differ from those of Cu2+ and Cd2+.
13. Takafumi Maeda, Akira Yasukouchi, Blood Lactate Disappearance during Breathing Hyperoxic Gas after Exercise in Two Different Physical Fitness Groups: on The Work Load Fixed at 70%VO2max, Applied Human Science, http://doi.org/10.2114/jpa.16.249, 16, 6, 249-256, 1997.10, The purpose of this study is to evaluate effects of breathing hyperoxic gas on blood lactate disappearance after submaximal exercise in two different physical fitness groups and to clarify the most effective oxygen concentration in each group. Fourteen healthy male students participated as subjects in this study. They were divided in two groups by difference in their anaerobic threshold (AT). Seven males were treated as Higher AT group and the others as Lower AT group. Subjects wore a T-shirt, short pants and sports shoes and performed three sessions; each consisting of five minutes of exercise and six minutes of rest, at a workload of 70% VO2max On a bicycle ergometer. Hyperoxic gas was breathed only during recovery periods. Oxygen rates of 21, 30, 40, 60, 80 and 100% in inspired gas were employed. According to the results of blood lactate (BLA), the most effective oxygen condition on BLA disappearance was obtained over 60% in Higher AT group and at 30% oxygen in Lower AT group. Thus, it was especially noteworthy that the effects of hyperoxic gas in Higher AT group were different from those of Lower AT group. It is thought that the effects of breathing hyperoxic gas were dependent on physical fitness, which have caused many reports to be in conflict hitherto..
14. Takafumi Maeda, Akira Yasukouchi, Blood Lactate Disappearance during Breathing Hyperoxic Gas after Exercise in Two Different Physical Fitness Groups: on The Work Load Fixed at 130%AT, Applied Human Science, http://doi.org/10.2114/jpa.17.33, 17, 2, 33-40, 1998.02, This study aimed to investigate the effects of hyperoxic gas breathing on the disappearance of blood lactate after exercise in two groups having different physical fitness and to determine the most effective O2 concentration in consideration of workload. Our previous study has demonstrated that hyperoxic gas breathing brought out different effects among subjects. In respect of these effects, it was thought necessary to pay attention to exercise intensity. Therefore, the exercise intensity of this study was set by using relative workload of anaerobic threshold (AT) from the aspect of blood lactate. Ten healthy male students participated as subjects and were divided into 2 groups; a group consisting of 5 active students whose mean AT was 60.4% VO2max (Higher AT group) and the other group consisting of 5 inactive students having the mean AT of 48.8% VO2max (Lower AT group). All subjects underwent three cycles of ergometer exercise on a bicycle (workload; 130% AT) for 5 min and recovery session for 6 min. The hyperoxic gas breathing was given only for the recovery session. The conditions of breathing were air, 30, 40, 60 or 80% O2. Blood for determination of the blood lactate level was taken only in the recovery session. When compared with air-breathing, the blood lactate level was significantly reduced in the condition of more than about 60% O2 breathing in Higher AT group, but not in Lower AT one. Together with the previous findings, it was found that the blood lactate level was markedly reduced by more than 60% O2 breathing in Higher AT group without relation to the workload in the range of about 70 to 80% VO2max. In Lower AT group, however, the effects of hyperoxic gas breathing were dependent on the exercise intensity; 30% and 40% O2 breathings were effective for the subjects with more than about 65% VO2max, but not in a lower intensity than it. These results indicate that the effects of hyperoxic gas breathing on the disappearance of blood lactate are dependent on the exercise intensity and the physical capacity..
15. Keita Ishibashi, Takafumi Maeda, Shigekazu Higuchi, Akira Yasukouchi, Error and Individual Difference in Cardiovascular Responses to Orthostatic Stress, Journal of Physiological Anthropology and Applied Human Science, http://doi.org/10.2114/jpa.24.339, 24, 4, 339-434, 2005.08, Variations in cardiovascular responses to orthostatic stress were investigated in terms of physiological polymorphism. Variations of physiological measurements are subdivided into individual differences and measurement errors. However, individual differences are often considered to be an error in statistical analysis due to its limitations in experimental design. In order to discuss about the relative contribution of individual difference in cardiovascular responses to postural changes, percent contribution (PC) was estimated using the Taguchi method. Six healthy male adults (age range: 21–27) were subjected to orthostatic stress by inducing a postural inclination of 60° head-up-tilting to the horizontal, and the responses were measured thrice in each subject on different days. The respective changes of heart rate (HR) and stroke volume (SV) in the period from the resting supine to the head-up-tilt position were significantly increased (p<0.01) and decreased (p<0.01) without affecting the mean blood pressure (MBP). The PC of individual difference in HR showed a significantly higher ratio of individual difference during the head-up-tilt (71.4–76.2%) compared with supine rest (0.0–50.4%). While the main variations of HR during supine rest were not the individual differences between the subjects, the day-to-day differences within the subject were significant. The PC of individual differences in MBP and SV constantly displayed a significant difference between the subjects. These results suggest that the strategy for maintaining stable cardiovascular regulation may be different even in normal subjects. In the perspective of physiological parameters, PC monitoring may serve as an empirical approach to evaluate physiological polymorphism..
16. Ishibashi K, Maeda T, Higuch S, Iwanaga K and Yasukouchi A, Comparison of cardiovascular response to sinusoidal and constant lower body negative pressure with reference to very mild whole-body heating, Journal of Physiological Anthropology, http://doi.org/10.1186/1880-6805-31-30, 31, 30, 2012.11, Background: The purpose of the present study was to compare sinusoidal versus constant lower body negative pressure (LBNP) with reference to very mild whole-body heating. Sinusoidal LBNP has a periodic load component (PLC) and a constant load component (CLC) of orthostatic stress, whereas constant LBNP has only a CLC. We tested two sinusoidal patterns (30-s and 180-s periods with 25 mmHg amplitude) of LBNP and a constant LBNP with −25 mmHg in 12 adult male subjects. Results: Although the CLC of all three LBNP conditions were configured with −25 mmHg, the mean arterial pressure (MAP) results showed a significantly large decrease from baseline in the 30-s period condition (P <0.01). In contrast, the other cardiovascular indices (heart rate (HR), stroke volume (SV), cardiac output (CO), basal thoracic impedance (Z0), total peripheral resistance (TPR), the natural logarithmic of the HF component (lnHF), and LF/HF (ln(LF/HF))) of heart rate variability (HRV) showed relatively small variations from baseline in the 30-s period condition (P <0.01). The result of the gain and phase of transfer function at the sinusoidal period of LBNP showed that the very mild whole-body heating augmented the orthostatic responses. Conclusion: These results revealed that the effect of the CLC of LBNP on cardiovascular adjustability was attenuated by the addition of the PLC to LBNP. Based on the results of suppressed HRV response from baseline in the 30-s period condition, we suggest that the attenuation may be caused by the suppression of the vagal responsiveness to LBNP..
17. Yoko Takagi, Hajime Harada, Takafumi Maeda, Masahiko Sato, Physiological Anthropology Design: a comparative study between Germany and Japan, Journal of Physiological Anthropology, http://doi.org/10.2114/jpa2.25.55, 25, 1, 55-57, 2006.02, With the recent globalization of industrial products, there is doubt as to whether the methodology of Physiological Anthropology has also been standardized. The purpose of this study is to assess signs of standardization through a comparative analysis of Physiological Anthropology design in Germany and Japan. This survey investigates its characteristics through four factors: comfort, usability, sensation and aesthetics. Both nations regard the first three indicators as important. The difference in assessment is, however, considerable. While German physiological anthropologists use subjective evaluation by means of questionnaires, somatometry and biomechanical analysis, their Japanese counterparts apply physiological measurements of the higher nervous system and the autonomic nervous system. Polymorphism and improving functional potentiality have recently gained increasing respect in Japan. Notions of aesthetics are not consciously analyzed in both countries. If the sense of beauty of product design relates to a physical and mental response, developing a systematic analysis on this factor would be a useful task for Physiological Anthropology..
18. Shigekazu Higuchi, Yutaka Motohashi, Keita Ishibashi, Takafumi Maeda, Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light, American Journal of Physiology, Regulatory, Integrative, and Comparative Physiology, http://dx.doi.org/10.1152/ajpregu.00355.2006, 292, 6, R2352-R2356, 2007.06, This experiment tested effects of human eye pigmentation depending on the ethnicity on suppression of nocturnal melatonin secretion by light. Ten healthy Caucasian males with blue, green, or light brown irises (light-eyed Caucasians) and 11 Asian males with dark brown irises (dark-eyed Asians) volunteered to participate in the study. The mean ages of the light-eyed Caucasians and dark-eyed Asians were 26.4 ± 3.2 and 25.3 ± 5.7 years, respectively. The subjects were exposed to light (1,000 lux) for 2 h at night. The starting time of exposure was set to 2 h before the time of peak salivary melatonin concentration of each subject, which was determined in a preliminary experiment. Salivary melatonin concentration and pupil size were measured before exposure to light and during exposure to light. The percentage of suppression of melatonin secretion by light was calculated. The percentage of suppression of melatonin secretion 2 h after the start of light exposure was significantly larger in light-eyed Caucasians (88.9 ± 4.2%) than in dark-eyed Asians (73.4 ± 20.0%) (P < 0.01). No significant difference was found between pupil sizes in light-eyed Caucasians and dark-eyed Asians. These results suggest that sensitivity of melatonin to light suppression is influenced by eye pigmentation and/or ethnicity..
19. Shigekazu Higuchi, Yutaka Motohashi, Takafumi Maeda, Keita Ishibashi, Relationship between Individual Difference in Melatonin Suppression by Light and Habitual Bedtime, Journal of Physiological Anthropology and Applied Human Science, http://doi.org/10.2114/jpa.24.419, 24, 4, 419-423, 2005.08, The purpose of this study was to determine the relationship between individual difference in melatonin suppression by exposure to light and habitual bedtime. Seventeen healthy male students (mean age: 22.6±2.4 yr) volunteered to participate in the study. The subjects were exposed to light (1000 lx) for 2 hours from 2 hours before the time of peak salivary melatonin concentration. Two hours after exposure to the light, melatonin suppression had occurred in fifteen subjects. No significant correlation was found between the rate of melatonin suppression and habitual bedtime in the fifteen subjects in whom melatonin suppression occurred. However, the habitual bedtime of the two subjects in whom melatonin suppression did not occur was earlier than that of the other subjects. These results suggest that there are some people with very low sensitivity to light and that this may affect habitual bedtime..
20. Shigekazu Higuchi, Yutaka Motohashi, Keita Ishibashi, Takafumi Maeda, Less exposure to daily ambient light in winter Increases sensitivity of melatonin to light suppression, Chronobiology International, http://dx.doi.org/10.1080/07420520601139805, 24, 1, 31-43, This study was carried out to examine the seasonal difference in the magnitude of the suppression of melatonin secretion induced by exposure to light in the late evening. The study was carried out in Akita (39° North, 140° East), in the northern part of Japan, where the duration of sunshine in winter is the shortest. Ten healthy male university students (mean age: 21.9±1.2 yrs) volunteered to participate twice in the study in winter (from January to February) and summer (from June to July) 2004. According to Japanese meteorological data, the duration of sunshine in Akita in the winter (50.5 h/month) is approximately one‐third of that in summer (159.7 h/month). Beginning one week prior to the start of the experiment, the level of daily ambient light to which each subject was exposed was recorded every minute using a small light sensor that was attached to the subject's wrist. In the first experiment, saliva samples were collected every hour over a period of 24 h in a dark experimental room (<15 lux) to determine peak salivary melatonin concentration. The second experiment was conducted after the first experiment to determine the percentage of melatonin suppression induced by exposure to light. The starting time of exposure to light was set 2 h before the time of peak salivary melatonin concentration detected in the first experiment. The subjects were exposed to light (1000 lux) for 2 h using white fluorescent lamps (4200 K). The percentage of suppression of melatonin by light was calculated on the basis of the melatonin concentration determined before the start of exposure to light. The percentage of suppression of melatonin 2 h after the start of exposure to light was significantly greater in winter (66.6±18.4%) than summer (37.2±33.2%), p<0.01). The integrated level of daily ambient light from rising time to bedtime in summer was approximately twice that in winter. The results suggest that the increase in suppression of melatonin by light in winter is caused by less exposure to daily ambient light..
21. Shintaro Yokoyama, Takafumi Maeda, Masashi Kuramae, Naoto Kakuta, Human thermal model expressing local characteristics of each segment, Journal of Human-Environmental System, http://doi.org/10.1618/jhes.10.51, 10, 2, 51-61, 2007.04.