When I was first starting my medical education, I did a research internship in a neuropharmacology department at my home university. The objective of my project was to assess depressive behaviour in rats. We would induce depression-like symptoms through chronic mild stress (CMS), an animal model of depression that is used to investigate the presence of depression-like syndrome by exposing the rats to various unpredictable stress sources and measuring their behaviours.
I will never forget the way those rats behaved after 36 straight hours of intense light exposure. In my eyes, food and water deprivation, isolation, and sudden tilting or wetting of the cages did not have as strong of an effect on their behaviour as the continuous light exposure. When I would come in to the lab to turn the lights off, I would find restless, aggressive rats, attacking each other and running desperately across their cages. Who would have thought that animals could be so vulnerable to changes in light?
Coming from Mexico City, where the seasonal change is almost nonexistent and the difference in daylight hours between summer and winter is less than three hours, my first November in Canada overwhelmed me.
I felt like one of these rats myself when I first arrived in Canada. Once the trees lost their beautiful autumn colours and the branches started waving naked toward the skies, dancing to the song of chilly winds, we all changed our clocks to wintertime. This meant that sunlight would be over at around 4:30 p.m.. Lights off in the middle of the afternoon. Coming from Mexico City, where the seasonal change is almost nonexistent and the difference in daylight hours between summer and winter is less than three hours, my first November in Canada overwhelmed me. After the time change, I would wake up with heavy feet; sleepiness would be my companion for the whole day. Coming home after work at 6 p.m., I would only feel like getting into my bed and letting the world around me disappear. It was as if the day was over as soon as the lights went off.
These bodily symptoms came with negative thoughts, sadness, and irritability. Everything in my life seemed darker, as if the lights in my brain had also been turned off. Obviously, the subsequent drops in temperature into the negative degrees did not help me feel better. I couldn’t fully understand this, seasonal change being a new phenomenon for me.
However, the sensations and feelings that I had that first November – that I wrote off as homesickness, loneliness, and consequences of my adaptation process – kept appearing in the following years when the days became shorter and colder. This group of symptoms, casually referred to as the “winter blues,” is called seasonal affective disorder (SAD). SAD is actually a type of depression that follows a seasonal pattern. This condition exists mostly in higher latitude countries, where there are more significant changes in daylight, temperature, and weather between seasons. According to the Centre for Addiction and Mental Health, up to 15 per cent of Canadians say they experience “winter blues” and 2 to 5 per cent suffer from severe symptoms and are actually diagnosed with SAD.
Susceptibility to SAD
Human beings, like all other mammals, have internal clocks that are sensitive to light. These internal clocks are groupings of interacting molecules in cells throughout the body. They are all coordinated by the suprachiasmatic nucleus – a “master-clock” – which is a group of neurons within the hypothalamus, located in the base of our brains. Our internal clocks generate circadian (daily) rhythms, internal endogenous (self-made) oscillations of about 24 hours that control behavioural patterns of sleep, appetite, as well as patterns of core body temperature, brain wave activity, and hormone production, among others.
Our complex biological clocks do not work on their own, but are rather modulated by the light-dark cycle. Daylight, perceived by the retina, inhibits the production of a hormone called melatonin, produced in the pineal gland. Melatonin is considered one of the main circadian hormones, because its production fits the 24-hour cycle. Its concentrations inform our body of the day-night cycle and thus help to adjust the internal biological clock. In this way, light acts as an external regulator of our circadian rhythms to help us adapt to our adapt to our environment – sleeping during the night and being awake during the day.
Considering this, it is understandable that not receiving daylight signals our bodies are used to may alter our circadian rhythms and have significant effects on our well-being. Several studies have shown that circadian cycles are more irregular in people that suffer from SAD than in people who don’t, deviating from the 24 hour-cycle, with hormones peaking at less predictable times. This is called the “phase-shift” phenomenon.
After my own experiences with SAD, I began to wonder: why are some people more vulnerable to changes in daylight and temperature? Is there a genetic predisposition to this disorder? Which population is more prone to this disorder and why? One possible explanation for is that the lack of sunlight leads to a failure in the production of the hormones we require to feel awake as well as an augmentation of the hormones like melatonin that make us feel tired and sluggish. This eventually leads to a disruption in our sleep-wake cycle and a tendency for low mood and depression. However, other factors may play a role, such as genetic predisposition to depression and the general vulnerability to mental health disorders.
Considering this, it is understandable that not receiving daylight signals our bodies are used to may alter our circadian rhythms and have significant effects on our wellbeing.
Some studies have looked at patterns of SAD in twins and families, revealing that there is a familial tendency to experience SAD. A study published in 2013 in the Journal of Affective Disorders explored SAD prevalence among the indigenous populations of Norway, Finland, Siberia, and Alaska. The research showed lower rates of SAD amongst these populations. It makes sense: residing at high northern latitudes for several generations may have adjusted the molecular mechanisms of their internal clocks, helping those groups to adapt to the reduced daylight of the Arctic Winter.
In 2002, the Norwegian Institute of Public Health conducted the Oslo Immigrants Health Study, and found that five immigrant groups that came from lower latitudes to Norway had a higher incidence of SAD than the native Norwegian and indigenous populations.
For those of us who must continue to grapple with this melancholic winter existence, there are certain ways to fight off the so-called winter blues. It could sound bizarre to say that sitting in front of a shiny box could help you with SAD – and no, I am not talking about your computer, but it works. Light therapy boxes, or phototherapy boxes are a special kind of lamp that have been proven effective in treating SAD. The therapy consists of sitting in front of the light box for 30 minutes to 2 hours – depending on the light intensity – to compensate for the lack of light on short winter days. Outside of these lamps, waking up early to catch some sun light, exercise, and the presence of plants can also help improve the mental health of those grappling with SAD. All in all, it is important that we who are dealing with SAD take care of ourselves, never ignoring symptoms that could be signs of decreasing mental health, and somehow find joy in this dark, depressing season.