Cortisol, known also as the 'stress hormone,' is a cortico-steroid hormone produced by the adrenal cortex. It follows a diurnal pattern with high values during the day and low values at night (Hollwich, 1979; Scheer and Buijs, 1999). It also exhibits a seasonal variation, with more stress hormones produced in summer than in winter (Erikson and Kuller, 1983; Kuller and Lindsten, 1992).
Abnormally high levels of cortisol increase blood pressure and blood sugar levels, may cause infertility in women, and suppress the immune system. At normal levels cortisol is involved in proper glucose metabolism, regulation of blood pressure, insulin release for blood sugar maintenance, and a healthy functioning immune system. Too much or too little cortisol has been implicated in numerous illnesses ranging from depression, cancer, and AIDS, to Alzheimer's disease (Sapse, 1997). Our body needs cortisol but only in the right amount.
Awakening is a strong stimulus to cortisol secretion and this awakening is influenced by light (Scheer and Buijs, 1999; Leproult et al., 2001). Office personnel working close to a window were found to have higher levels of morning cortisol during summer than during winter because daylight suppresses the production of melatonin and stimulates the secretion of cortisol, making people feel more alert and active, according to a study by Erikson and Kuller (1983). Daylight intensities found in the morning produce optimal levels of serotonin to engender a state of high alertness but not stress. Year-long observation of school children by Kuller and Lindsten (1992) indicated that high values of cortisol during winter correlated with low rates of absence because of illness. Moreover, high values of morning cortisol were associated with an inclination towards sociability and alertness. These findings explain why students with adequate exposure to daylight performed better than students with less exposure, as will be seen in Chapter 5.
Clearly, light acts on the production of cortisol, serotonin, and melatonin, three important hormones that affect our internal clock and our mood states, among many other effects. It is important to keep these hormones in proper balance. Low levels of serotonin (the daylight hormone) together with a low level of norepinephrine cause depression. Sluggish serotonin secretion may also account for the emotional, appetite, libido, and sleep disturbances associated with depression. Light therapy, be it artificial or natural, has been found to be an effective antidepressant but only when the light is bright enough. A proportional relationship exists between the intensity of light and the effectiveness of the therapy: 10 000 lux worked three times faster than 2500 lux in alleviating winter depression. Researchers now speculate that by using light as a therapeutic agent, 80% of SAD sufferers can be cured. Studies, as we have noted, have also found that the effectiveness of light therapy depends not only on the intensity of light but also on the duration of exposure and its spectral quality. One can conclude that because of its numerous positive attributes, natural light is one of the best antidepressant agents available, one that is more efficient than electric light. It is almost impossible to illuminate a building with light at levels of 2500 lux or even 10 000 lux, that combat depression. Such illumination, however, can be achieved with natural light. On a sunny day, the illuminance outside can be as high as 100 000 lux and on a cloudy day it may reach 20 000 lux. What is interesting to point out to architects is that we spend the majority of our lifetime indoors because of weather and the necessities of work. It is, therefore, all the more important for architects to design buildings that provide therapeutic light levels, preferably with daylight. Buildings should be designed not only as places for shelter and to house necessary activities but also as places for healing.
Traditional daylighting solutions relying on windows in the walls only, the solution adopted nowadays by builders of most multistory buildings, are very limited when it comes to alleviating SAD. The high levels of daylight that people require are confined to the peripheral area that is barely a few feet deep, normally not exceeding one and half times the height of the window. Daylight levels drop precipitously as one moves away from the window. Other more innovative solutions are needed to bring high levels of daylight to the central areas of the building and to the areas where the majority of workers are located most of the day. Light levels can drop by 50% or more by simply moving a few feet away from the window. Of course, it is possible to supplement the high light levels needed to combat SAD by using electric light, but with concerns about the depletion of fossil fuels and global warming, that solution may prove too costly. It falls, therefore, on architects to design buildings where daylight is plentiful throughout the building interior, not just the periphery. These high light levels should fall on the occupant's eyes, the first receptor in the light therapy process. Architects should concern themselves with furniture layouts that encourage building occupants to face windows instead of walls to maximize the effectiveness of light therapy.
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