More light and less sudden changes in time

The European Union is currently debating the desirability of eliminating the change of time. Making the most of daylight hours was what motivated the introduction of delay and advancement of the clock depending on the seasons. And the truth is that the ambient light has a special importance for the health and quality of life of people, as has been demonstrated by science. Subjecting them to abrupt changes can alter biological rhythms and health.

The daily changes in the luminous environment, in the schedules of different work shifts, in the shortening of the days in winter or in the Transmeridian air travel are often associated with mental, emotional and health problems, such as the low performance in Physical or intellectual work, mood swings, jet lagdiscomfort, depression or seasonal affective disorder.

Daily changes in the luminous environment, by shifts of work, or shortening of the days in winter are associated with mental, emotional and health problems

A very important function of the ambient light is to synchronize the internal biological clocks of our body with the solar day/night cycle. How does it work? The main of these watches is the suprachiasmatic nucleus of the hypothalamus. It is a powerful brain clock, with great functional autonomy, which synchronizes our times of sleep and wakefulness, the body temperature and the pace of production of many hormones and physiological activities with the cycle of ambient light-darkness. It contains about 10,000 neurons on each side of the brain, which permanently receive information from the outside light from the retina of each eye and through the optic nerve.

The clock in the suprachiasmatic nucleus of the brain is not perfect, because it delays. We know this because when a person is kept for several days in a constant luminous environment, where there are no cycles or changes of light, he goes to sleep every day a little later, being able to arrive a time in which he has invested the natural cycle, because he sleeps by day and is awake from Night. But that usually does not happen, because the morning light puts every day in time our inner circadian clock. It is a function that can also perform other external stimuli, such as alarm clock, garbage truck that passes at the same time every day or noise that makes the next door neighbor when you shower every morning. This function was baptized by the German scientific literature with the name of Zeitgeber (Giver of time), term which has already been adopted also in other countries. Light is the most powerful zeitgeber we know.

But how does environmental light information get to the suprachiasmatic nucleus of the brain? A long time ago there was an interesting observation that surprised the scientists: a group of blind people, although they could not detect visual images, they could detect the light. Similarly, some genetically modified mice to not have cones and canes in the retina, also detected the light of each morning. These findings led to the discovery of the existence in the human retina of a small fraction of ganglion cells, about 4% and at least 5 different subtypes. These cells synthesize the photopigment melanopsin and thus are able to receive directly the light — like cones and canes —, convert it into electrical activity and send that activity to the suprachiasmatic nucleus of the brain through the optic nerve.

Electronic devices suppress the release of melatonin and delay circadian rhythms

photosensitive ganglion cells, in addition to sending light-related information to the suprachiasmatic nucleus, also send it to other large areas of the brain involved in the regulation of sleep and wakefulness, cognition, emotions and the state of People's spirits.

To this we must add the role of melatonin, a hormone released by the pineal gland of the brain that increases at night, coinciding with the onset of sleep and is maintained throughout the period of darkness. Melatonin favors sleep with a rhythm and intensity of inverse release to light/dark (more light, less melatonin; to more darkness, more melatonin), which makes it another important internal temporal signal of the mammalian brain. Electronic devices, which are generally very rich in light, suppress the release of melatonin and delay circadian rhythms and the onset of sleep, thus increasing morning drowsiness, especially in those who abuse these devices at High hours of the day.

Thanks to these mechanisms, the brain attaches the biological rhythms of the organism's functioning to the changes in light that nature slowly establishes as the seasons of the year occur. When these changes are abrupt and artificially imposed, these mechanisms have difficulty adjusting and slow to do so, which is reflected in the mental, emotional and health alterations mentioned above.

When a person is held for several days in a constant luminous environment, he can end up reversing the natural cycle

People with seasonal affective disorder — very typical of populations living in high latitudes where the duration of the day is lower and the seasonal, stronger changes — also have altered the production and release rates of melatonin. and other types of patients, manic-depressive, have altered moods. They usually depressed at the beginning of the fall, when the ambient light decreases and they are stimulated when it rises again in the spring. They tend to work the therapeutic treatments consistent in times of exposure to bright light. The blue light (480 nm of frequency) is the one that most activates the melanopsin, the photopigmentation of the ganglion cells sensitive to the light, so it is not strange that it is also the type of light with more capacity to activate regions of the brain involved in attention , alert and emotional processes, even in blind people.

All this gives us the idea of the powerful influence that environmental light and its changes can have, not only to regulate sleep and wakefulness, but also to follow naturally and without problems the seasonal changes or modulate cognition and humour. It also explains how sudden changes in artificially-imposed luminosity can affect people's health and quality of life. It is a knowledge that, together with other considerations such as economics, governments and administrations should take into account when establishing abrupt timetable changes in their respective countries.