Effects of bright or dim light during the daytime on digestive activity in humans

Bright daylight produces negative effects on affective and cognitive outcomes in nocturnal rats

The daily light/dark cycle affects animals' learning, memory, and cognition. Exposure to insufficient daylight illumination negatively impacts emotion and cognition, leading to seasonal affective disorder characterized by depression, anxiety, low motivation, and cognitive impairment in diurnal animals. However, how this affects memory, learning, and cognition in nocturnal rodents is largely unknown. Here, we studied the effect of daytime light illuminance on memory, learning, cognition, and expression of mRNA levels in the hippocampus, thalamus, and cortex, the higher-order learning centers. Two experiments were performed. In experiment one, rats were exposed to 12 L:12D (12 h light and 12 h dark) with a 10, 100, or 1000 lx daytime light illuminance. After 30 days, various behavioral tests (novel object recognition test, hole board test, elevated plus maze test, radial arm maze, and passive avoidance test) were performed. In experiment 2, rats since birth were raised either under constant bright light (250 lx; LL) or a daily light-dark cycle (12 L:12D). After four months, behavioral tests (novel object recognition test, hole board test, elevated plus maze test, radial arm maze, passive avoidance test, Morris water maze, and Y-maze tests) were performed. At the end of experiments, rats were sampled, and mRNA expression of Brain-Derived Neurotrophic Factor (Bdnf), Tyrosine kinase (Trk), microRNA132 (miR132), Neurogranin (Ng), Growth Associated Protein 43 (Gap-43), cAMP Response Element-Binding Protein (Crebp), Glycogen synthase kinase-3β (Gsk3β), and Tumour necrosis factor-α (Tnf-α) were measured in the hippocampus, cortex, and thalamus of individual rats. Our results show that exposure to bright daylight (100 and 1000 lx; experiment 1) or constant light (experiment 2) compromises memory, learning, and cognition. Suppressed expression levels of these mRNA were also observed in the hypothalamus, cortex, and thalamus. These results suggest that light affects differently to different groups of animals.

Studying the Optimal Time for Meals to Circadian Rhythms and Body Health (Application to Hospitality Establishments)

Circadian rhythms, metabolism, and nutrition are closely linked, although the effects of meal timing on the human circadian system are poorly understood. The time factor biological of nature is an essential element for the functioning of cosmic systems. In the event of any defect, many problems come out as a result of this imbalance, and here came whether to change the timing of eating diets has to do with the occurrence of illness in the body and the emergence of diseases of this age such as obesity and diseases of the gastrointestinal tract (gallbladder - diseases of the colon, liver, and others). Hence the need to research the effect of timing, eating the three meals, and the body's system to resist disease. The study sample was withdrawn from Egyptian and foreign guests in hospitality establishments in Hurghada, Egypt with 300 forms. SPSS statistical program was used, and the research was focused on the body's sympathetic nervous system and its role in regulating the body processes related to metabolism. The timing of waking up and eating meals reached a set of findings and recommendations. The most important ones are the need to amend the healthy track of food and to increase the awareness of educational health, followed by hotels and resorts’ restaurants and room services offering those meals according to the client’s demand and the time they want to eat the meal. Therefore, it is necessary to direct the food operators in the hospitality establishments to prepare the food at the optimum time and to search for the modification of new food trends in line with the nature and the regularity of the diet to prevent diseases.

Light as a modulator of emotion and cognition: Lessons learned from studying a diurnal rodent

Light profoundly affects the behavior and physiology of almost all animals, including humans. One such effect in humans is that the level of illumination during the day positively contributes to affective well-being and cognitive function. However, the neural mechanisms underlying the effects of daytime light intensity on affect and cognition are poorly understood. One barrier for progress in this area is that almost all laboratory animal models studied are nocturnal. There are substantial differences in how light affects nocturnal and diurnal species, e.g., light induces sleep in nocturnal mammals but wakefulness in diurnal ones, like humans. Therefore, the mechanisms through which light modulates affect and cognition must differ between the chronotypes. To further understand the neural pathways mediating how ambient light modulates affect and cognition, our recent work has developed a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus), in which daytime light intensity is chronically manipulated in grass rats housed under the same 12:12 hour light/dark cycle. This simulates lighting conditions during summer-like bright sunny days vs. winter-like dim cloudy days. Our work has revealed that chronic dim daylight intensity results in higher depression- and anxiety-like behaviors, as well as impaired spatial learning and memory. Furthermore, we have found that hypothalamic orexin is a mediator of these effects. A better understanding of how changes in daytime light intensity impinge upon the neural substrates involved in affect and cognition will lead to novel preventive and therapeutic strategies for seasonal affective disorder, as well as for non-seasonal emotional or cognitive impairments associated with light deficiency.

Seasonal variation in amount of unabsorbed dietary carbohydrate from the intestine after breakfast in Japanese subjects

We previously showed that daytime dim-light exposure has a negative effect on the efficiency of dietary carbohydrate absorption in the evening, whereas evening-time dim-light exposure has a beneficial effect. These results suggest that seasonal changes in the environmental light may affect gastrointestinal activity, and that there might, therefore, be seasonal variation in the efficiency of dietary carbohydrate absorption from the intestine. In order to prove this hypothesis, we measured the amount of dietary carbohydrate unabsorbed from the intestine after a breakfast in healthy female Japanese subjects during the four seasons of the year. We estimated the amount of unabsorbed dietary carbohydrate by the breath hydrogen test, which measures the amount of hydrogen in exhaled air. A 6 g solution of lactosucrose, an indigestible trisaccharide, was used for comparison. Two groups of subjects, 12 subjects in Osaka and 14 subjects in Nagano, were studied in the winter (January to February), spring (April to May), summer (July to August), and autumn (October to November) of 2004. We found the following results: (1) In no season were there any significant differences between the two subgroups in the orocecal transit time of the breakfast and the lactosucrose solution. Nor were there any significant differences in the amount of unabsorbed dietary carbohydrate from the breakfast. (2) Using the pooled data of the total of 26 subjects, there was no significant seasonal variation in the orocecal transit time of the breakfast or the lactosucrose solution. (3) There was a significant seasonal variation in the amount of unabsorbed dietary carbohydrate from the breakfast. (4) The amount of unabsorbed dietary carbohydrate from the breakfast was largest in winter and smallest in autumn. Results in spring and in summer were similar and intermediate between those in winter and autumn. Post hoc multiple comparison tests showed that the amount of unabsorbed dietary carbohydrate in winter was significantly larger than in autumn. (5) In winter, the average ratio of the amount of unabsorbed dietary carbohydrate to the total amount of carbohydrate in the breakfast was about 12%; in autumn it was about 6%. These results clearly show that there is seasonal variation in the efficiency of intestinal dietary carbohydrate absorption among young female Japanese subjects.

Comparison of carbohydrate digestion between Japanese and Polish healthy subjects

We have revealed that light environment affects digestion and absorption of dietary carbohydrates in the gastrointestinal tract. This experimental result supposes that the efficiency of carbohydrate absorption may differ among people who live in different latitudes, such as Japanese and Polish people, at the same calendar season. In order to prove this hypothesis, we have been comparing the efficiency of carbohydrate absorption using the breath hydrogen test in Japan and Poland. Here, we report the comparison of the result obtained in the summer of 2004 as the following; (1) Orocecal transit time (OCTT) for indigestible trisaccharide of Japanese subjects was significantly longer than that in Poland (p = 0.043). (2) On the ingestion of minestrone, the amount of unabsorbed carbohydrate of Japanese subjects (which was estimated as trisaccharide equivalent) was significantly larger than that of Polish subjects (p = 0.006).

Effect of evening exposure to dim or bright light on the digestion of carbohydrate in the supper meal

In a previous study we found that daytime exposure to bright as compared to dim light exerted a beneficial effect on the digestion of the evening meal. This finding prompted us to examine whether the digestion of the evening meal is also affected by evening light intensity. Subjects lived in light of 200 lux during the daytime (08:00-17:00 h) and took their evening meal at 17:00 h under 20 lux (evening dim-light condition: 17:00-02:00 h) or 2000 lux (evening bright-light condition: 17:00-02:00 h) until retiring at 02:00 h. Assessment of carbohydrate digestion of the evening meal was accomplished by a breath hydrogen test that is indicative of the malabsorption of dietary carbohydrate. Hydrogen excretion in the breath in the evening under the dim-light condition was significantly less than under the bright-light condition (p < 0.05). This finding is the opposite to that obtained in previous experiments in which subjects were exposed to the different intensities of light during the daytime, and indicates that the exposure to dim light in the evening exerts a better effect on carbohydrate digestion in the evening meal than does the exposure to bright light.

Effects of dim or bright-light exposure during the daytime on human gastrointestinal activity

On the basis of our previous findings that bright-light exposure during the daytime has profound influence on physiological parameters such as melatonin secretion and tympanic temperature in humans, we proposed the hypothesis that bright vs. dim light-exposure during the daytime has a different influence on the activity of the digestive system via the endocrine and/or autonomic nervous system. To examine this hypothesis, we conducted a series of counterbalanced experiments in which subjects stayed the daytime (7:00 to 15:00h) under either a dim (80 lux) or bright (5,000 lux) light condition. We measured gastrointestinal activity using a breath hydrogen (indicative of carbohydrate malabsorption) and an electrogastrography (EGG, indicative of gastric myoelectric activity) test. The results showed the postprandial breath hydrogen excretion during the following nighttime period after daytime exposure to the dim-light condition was significantly higher than under the bright-light condition (p < 0.05). In addition, the spectrum total power of the EGG recorded after taking the evening meal was significantly lower for the dim than bright-light condition (p < 0.05). These results support our hypothesis and indicate that dim-light exposure during the daytime suppresses the digestion of the evening meal, resulting in malabsorption of dietary carbohydrates in it.

Effect of postprandial posture on digestion and absorption of dietary carbohydrate

The effect of postprandial body posture on digestion and absorption of dietary carbohydrate were examined through breath hydrogen test on 6 female subjects. During the experiment, the participants either sat on a chair or lay on their backs for the first 4 hr (from 08:00 to 12:00) after eating the test breakfast meal. They then remained sedentary on a sofa for 6 hr (12:00 to 18:00). Participants' end alveolar breath samples were collected for 10 hr (every 15 min from 08:00 to 12:30, and then every 30 min until 18:00). The experiment was conducted on two consecutive days using a randomized, crossover study design. The results demonstrated that in the supine position orocecal transit time of the test meal was significantly slower than in the sitting position (260 +/- 21 min and 238 +/- 20 min, respectively, p < 0.01). In addition, afternoon breath hydrogen excretion due to a partial malabsorption of dietary carbohydrate and its fermentation in the colon was significantly larger in the sitting position (144.0 +/- 24.1 ppm.hr) than in the supine position (110.0 +/- 26.1 ppm.hr, p < 0.05). These results support the hypothesis that there was a marked effect of postprandial body posture on the function of the digestive system. The present findings suggest that the postprandial supine position is preferable to the sitting position for the digestion and absorption of dietary carbohydrate.