Winter depression might not actually exist

It’s not uncommon for people to think that the depression they experience in winter is caused by the season. The days are short and dark; who wouldn’t start feeling down? But Wim Winthorst hasn’t been able to find any evidence of the phenomenon.
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Door Christien Boomsma

18 February om 16:45 uur.
Laatst gewijzigd op 22 November 2020
om 16:15 uur.
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By Christien Boomsma

February 18 at 16:45 PM.
Last modified on November 22, 2020
at 16:15 PM.
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Christien Boomsma

Achtergrondcoördinator en wetenschapsredacteur Volledig bio »
Background coordinator and science editor Full bio »

Some explanations sound so good that they simply must be true. Like how working out makes you sleep better. Or that sugar makes children hyperactive. Or that more people suffer from depression in winter.

Approximately 8 percent of the Dutch population claims to get the winter blues. When the days get shorter and the rain lashes against the windows, they feel gloomy. Three percent of people even say they suffer from seasonal depression: a returning depression that gets worse in winter and clears up in spring.

‘It’s really difficult to measure’, says psychiatrist Wim Winthorst with the University Centre for Psychiatry at the UMCG. He studied the phenomenon and will receive his PhD for his findings this month. ‘Depression is a catch-all term that varies per person.’ 

To count as seasonal, a depression has to have started at least two years ago. Patients are extremely tired and don’t feel properly awake until later in the day. They eat a lot and feel downcast. If there is any other reason a person might feel sad, like unemployment because of seasonal work or the recent death of a loved one, it’s not seasonal depression.

Light therapy

Fortunately for the thousands of people suffering from these complaints, there is an effective treatment. Doctors can prescribe light therapy: patients go to the UMCG at eight in the morning to sit down in front of a daylight lamp the size of a television screen. The treatment takes thirty to forty-five minutes. 

Depression is a catch-all term that varies per person

‘The treatment lasts for about a week, after which a lot of people say they’re feeling better’, says Winthorst. Approximately 70 percent of patients improve after the treatment. ‘It’s a quick and elegant form of therapy with few side effects.’

Here’s the weird part, though: when Winthorst tried to study the phenomenon of seasonal depression, he had trouble finding any ‘real’ patients. ‘We looked at the data from people in the long-term NESDA study, the Netherlands Study of Depression and Anxiety. We also used data from the internet study HoeGekIsNL, which has been studying the mental health of the Dutch population since 2014, and a screening questionnaire, the SPAQ, for seasonal complaints. Across that whole group, there’s actually very little difference between the seasons.’

Unexpected results

He looked at the data of thousands of people in the Netherlands but found almost no cases of winter depression. ‘If you ask people whether certain seasons are more difficult for them, they’ll say yes’, Winthorst concludes. For healthy people, i.e. anyone not suffering from depression or anxiety, this number is 49 percent. The percentage increases to 65 percent as the mental problems of respondents get worse. ‘However, those people don’t actually suffer from depression in winter more than others.’ 

These results took Winthorst by surprise. ‘When I started my research, I thought it was cut and dried. I wanted to look into the biological reasons for seasonal depression – the lack of light – and see if people’s symptoms reflected this.’

He wouldn’t go so far as to say that seasonal depression doesn’t exist. Most of his measurements were only single measurements and his results might have been different if he’d followed people throughout the year. On top of that, the data he used wasn’t collected with the express intent of studying seasonal depression. 

We experience winter differently than we do summer

But it is peculiar that thousands of people claim to suffer from the phenomenon, and that the treatment for it is effective. What’s going on?

Winthorst thinks it’s partially to do with memory. ‘We experience winter differently than we do summer’, he says. ‘But the question is whether this actually leads to depression. How strong is this phenomenon?’ The theory that depression is caused by a lack of light which leads to overproduction of the sleep hormone melatonin is also an attractive one. The fact that people feel better after light therapy means there’s practically no reason to doubt the existence of this kind of depression. 

Real symptoms

Is it time to put an end to light therapy? Is it wasted money, better spent on something else? 

Winthorst shakes his head no. Absolutely not. We might not be able to definitively point to winter as the cause of feelings of depression, ‘but the symptoms are real, and they do really go away. The only problem is that the explanation for the symptoms disappearing can’t be proven’.

The same can be said for many other treatments, says Winthorst. ‘In medical science, we want to see a cause, the illness that results from that cause, and a therapy to treat it. Like the cholera bacterium for example: it causes stomach cramps and can be treated with antibiotics and fluid. But in psychiatry, it’s not that easy.’

They only ever clearly diagnose the cause of people’s symptoms in a small percentage of cases

In his field, says Winthorst, 70 percent of treatment results are due to the so-called non-specific factors. ‘Any kind of treatment can make people feel better.’ This could be due to good doctor-patient contact, the treatment structure, and the treatment rationale. ‘That’s when you and your therapist agree on the cause and that this treatment could work.’ Only 8 percent of treatment results are due to a specific therapy. 

Thinking differently

This phenomenon can also be found in other areas of healthcare. ‘Take the internal medicine clinic, for instance. They only ever clearly diagnose the cause of people’s symptoms in a small percentage of cases. But the people without a clear diagnosis are still in actual pain.’

Nevertheless, research only focuses on that 8 percent. ‘When we can’t find the answer there, we just say that it doesn’t exist’, says Winthorst. ‘But when you scraped your knee as a kid and your mother kissed it better, the pain really did go away. Does that mean the pain wasn’t real?’

Winthorst says we need to get rid of this way of thinking. ‘Someone asked me the other day: if you had a million euros, would you spend it on researching seasonal depression? But I’d rather have eight million and spend just one million on seasonal depression and the other seven on those non-specific factors. Anything I’d find would apply not just to seasonal depression, but also to treatments at the internist, the general practitioner, to medical treatment. To anything.’


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