As the days grow shorter and the crisp air of winter sets in, it’s common to feel a little less energetic, a little more sluggish.
For some, however, this seasonal shift isn’t just a minor mood change—it can trigger seasonal affective disorder (SAD), a type of depression that can be overwhelming and difficult to manage.
In exciting news for the medical world, scientists at the University of Copenhagen may have just uncovered a biological reason behind why some people experience severe winter blues, while others embrace the colder months without skipping a beat.
What they found could pave the way for more targeted treatments and a deeper understanding of how our bodies interact with the changing seasons.
So, why do some people love the winter, while others struggle with SAD?
The answer lies in the brain’s ability to process serotonin, the “feel-good” hormone linked to mood regulation.
Brain scans have revealed a startling difference between people who suffer from SAD and those who thrive in winter—specifically, it all comes down to the way the brain manages serotonin.
A Biological Insight into Winter Blues
You’ve probably heard of serotonin as the chemical responsible for making us feel happy and content.
When you’re feeling good, it’s often because serotonin is working its magic in your brain.
However, during the winter months, serotonin levels can fluctuate, and this change can trigger or exacerbate the symptoms of seasonal affective disorder.
Research from Copenhagen has provided a key biological insight into why some people feel the weight of winter far more than others.
The culprit?
Serotonin transporter (SERT).
SERT is a protein that plays a crucial role in regulating serotonin levels. It’s essentially responsible for transporting serotonin back into nerve cells, where it becomes inactive.
The issue is that when SERT levels increase, serotonin becomes less available to boost mood, leading to those dreaded feelings of sadness and fatigue.
The Winter SERT Mystery
So, what happens in winter that causes some people’s serotonin levels to dip significantly?
According to Brenda McMahon, the neurobiologist leading the study, the brain “turns a dial” to adjust serotonin production when the seasons change.
During the winter months, the serotonin transporter (SERT) is ramped up in people with SAD, meaning more serotonin gets pulled into the nerve cells, leaving less available for mood regulation.
“We believe that we have found the dial the brain turns when it has to adjust serotonin to the changing seasons,” McMahon said in an interview with the BBC.
“The serotonin transporter (SERT) carries serotonin back into the nerve cells where it is not active—so the higher the SERT activity, the lower the activity of serotonin.”
This mechanism doesn’t affect everyone the same way, though.
While some people’s brains increase the production of SERT as the days get shorter, others remain unaffected, and their serotonin levels stay high, even through the darkest days of winter.
But for those who do experience the increase in SERT production, it’s no surprise that the winter months bring about those feelings of sadness, lethargy, and irritability.
The Science Behind the SERT Discovery
To dig deeper into the relationship between SERT levels and SAD, the research team at the University of Copenhagen conducted a study using positron emission tomography (PET) brain scans.
This technology allowed them to track changes in SERT activity in the brain across different seasons.
The results were startling: People with SAD had higher levels of SERT in their brains during the winter months compared to their healthy counterparts.
In contrast, healthy volunteers exhibited similar levels of SERT throughout the year, with no noticeable seasonal fluctuation.
Interestingly, this change wasn’t observed in the summer.
Both groups—those with SAD and healthy participants—had similar amounts of SERT in their brains when the sun was shining bright and the days were long.
But as the nights grew longer, those with SAD experienced a significant uptick in SERT production, leading to lower serotonin activity during the winter months.
“Sunlight keeps this setting naturally low, but when the nights grow longer during the autumn, the SERT levels increase, resulting in diminishing active serotonin levels,” McMahon explained.
What Sets SAD Apart from Winter Enjoyment?
But why do some people experience these seasonal changes in SERT levels while others don’t?
According to McMahon and her team, the difference comes down to genetics and individual brain chemistry.
Not everyone’s brain is wired to increase SERT production during the fall and winter months, which might explain why some people experience no change in mood and energy as the season shifts.
Interestingly, the study found that those unaffected by SAD tend to maintain high serotonin levels throughout the winter, which helps them feel energized and motivated, even during the darkest days.
The takeaway is clear: the brain’s ability to regulate serotonin in response to changing seasons plays a pivotal role in whether or not a person experiences seasonal affective disorder.
A Promising Step Forward in SAD Treatment
Though this study is still in its early stages and the sample size was small, its implications are exciting.
For years, researchers have suspected that fluctuations in serotonin, and particularly the role of SERT, are connected to SAD.
This research not only confirms that belief but also offers concrete biological evidence that could lead to better treatment options.
For instance, treatments targeting SERT levels could potentially help people with SAD maintain more stable serotonin activity during the winter months.
Additionally, this study provides new insights into the role of sunlight in regulating serotonin.
We’ve long known that light therapy can alleviate symptoms of SAD, but now we have a better understanding of why it works.
Sunlight helps regulate SERT levels, keeping serotonin in an active, mood-boosting state.
However, as Sam Challis, an information manager at the British mental health charity Mind, notes:
“We don’t yet know enough about how serotonin levels can be affected by light levels, so this is quite an interesting, albeit small, study. We would welcome more research.”
Next Steps: What Lies Ahead for SAD Research?
So, where do we go from here?
As McMahon and her team continue to explore the role of SERT and serotonin in SAD, there are many exciting avenues for future research.
For one, scientists are keen to learn more about why some people’s brains ramp up SERT production in response to shorter days, while others remain unaffected.
This could lead to personalized treatments for individuals with SAD, allowing doctors to tailor interventions based on their unique brain chemistry.
As for now, 12 million people across northern Europe are estimated to experience SAD, and the results of this study could help millions of individuals better understand their symptoms and find effective treatments.
It’s clear that SAD is a multifaceted condition, and while we’re not yet ready to offer a one-size-fits-all solution, this research brings us one step closer to alleviating the burden of seasonal depression.
A Brighter Future for Winter’s Darkest Days
Though winter might always bring challenges for some, understanding the biological basis of seasonal affective disorder is the first step toward offering hope.
Whether through light therapy, targeted medications, or lifestyle changes, we now have a deeper understanding of why some of us experience those “winter blues” and, more importantly, how we can better manage them.
So, while the days may get shorter and the nights longer, this new research offers a glimmer of light at the end of the tunnel for those who feel the weight of winter the hardest.
And with more research on the horizon, the future looks bright for those seeking a cure for the winter blues.
