The winter solstice has arrived. Effects of dark days on the human body

Our bodies are ready to celebrate the return of the sun

Written by Gary Stix Edited by Dean Visser

This year’s December solstice, the moment when Earth’s northern hemisphere is furthest from the sun, is on the 21st, but it’s more than just a landmark on the calendar. It is also defined by how our body reacts to the event. The dimming of our daily intake of natural light leading up to the winter solstice causes a series of notable physiological changes.

These changes are related to circadian rhythms. The word circadian comes from the Latin word “circadian”.Around the 2nd day,It means “about 1 day”. It describes how animals, plants, fungi, and bacteria respond to environmental signals, such as light input, on a daily and seasonal basis.

Sophia Axelrod is a chronobiologist at Rockefeller University who studies circadian rhythms and their effects on physiology and behavior. Her research on circadian rhythms, sleep, and lifespan in the laboratory of Nobel Prize-winning author Michael Young led her to discover how the summer solstice and the dark days leading up to it affect fruit flies (the animal she began studying). This made him an ideal candidate to ask about his impact. ) to humans.

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(An edited transcript of the interview follows:)

In high latitude regions, what happens to our body rhythms on the shortest day of the year?

Our body rhythms are determined by light. For example, if you travel from east to west and the light changes, your body clock may become out of sync with real time. The same thing happens during the shortest days of the year, as there are four to eight hours of daylight earlier in summer than in winter. In my hometown of Berlin, the sun rises at 3:45 a.m. on June 21st and 8:15 a.m. on December 21st. This means that at the moment I don’t get a sunrise signal until several hours later when I have to get up to go to school. Or work makes you feel bad and unhealthy for your circadian rhythm. So, the onset of circadian stimulation should be delayed to signal to the body, through the eyes and specialized brain structures, that it is time to start activating (transcribing and translating) a set of so-called clock genes. It is the secretary of every cell and tells other cells what to do and when.

In addition, it gets dark very early in Berlin, at 3:56 pm, so there isn’t enough sunlight throughout the day. There is a dark period before falling asleep, which can have a negative impact on people’s mood, energy levels and sleep, worsening ‘sunset’ in older people with dementia and causing confusion, agitation and sleep disturbances. .

How do people with sleep disorders react?

What we see in winter is that when people are left to their own devices, they are slower to get out of bed because they don’t have the light stimulation to start the day. Additionally, in modern society, the influence of indoor lighting has caused significant changes in sleep/wake times.

We all go through this. It’s very difficult to get out of bed when it’s pitch black, and conversely, in the summer, if you’re in a very bright room and are exposed to a lot of early morning sunlight at 4 a.m., it’s difficult to sleep. Are all of these good for your health? Isn’t it healthy? What I have just described does not suggest either method.

However, sensitivity to light varies from person to person. Generally this is fine as long as it doesn’t interfere with functionality in some way. Without light, many people have difficulty getting out of bed and have difficulty with daytime activities. The problem is complicated by the fact that lack of sunlight in winter causes seasonal affective disorder, a phenomenon in which circadian rhythms are disrupted and people become really depressed. And it is a reality completely caused by a lack of light.

It’s not just the shortest day of the year in terms of the time the sun rises. This is also the overall light level at high latitudes. Where I am in New York City, some days can be very dim. Light levels never reach the amount or dose needed to direct circadian rhythms. If such an environment persists for a long period of time, the circadian clock becomes severely disrupted and basically no longer plays its role in organizing cellular functions. And one of the consequences is depression.

Are effects such as depression particularly severe during the period around the winter solstice?

Yes, especially for those who get up early, go to work in basically the dark, sit in a windowless office with indoor lighting and no circadian stimulation, and then come home after dark again. Basically, they potentially week In complete circadian darkness. And, of course, all this is most severe around the summer solstice, when the days are the shortest of the year, but then it gets better again. Some people in some cultures describe this as a reawakening, but it is actually a reawakening of the circadian clock.

Are there other effects besides depression? How does the summer solstice affect resistance to infectious diseases?

All cells have circadian rhythms. Even though it’s winter, if you don’t get enough light, your immune system will be weakened. The production of immune cells (T cells and macrophages) needed to fight infections is stopped at certain times of the day. Less light reduces immune system function and reduces resistance to infection.

There are discussions about abolishing daylight saving time, including from the next presidential administration. Is that a good thing?

You change your body twice a year due to daylight saving time, which causes jet lag. This may not be a big deal for a particular individual, but statistically it’s a big deal at the population level. The next day, heart attacks and traffic accidents skyrocket. It’s an unnecessary thing that we control the whole country and we need to get rid of it.