Seasonal affective disorder: why winter pulls you under

“Every year it’s the same. In November I switch off and in March I come back on.” A woman told me this at the end of October, because she knew what was coming. She was not frightened. She was tired of being told every year to try a little harder.

Seasonal dips in mood have a particular status in Slovenia: everybody knows about them and almost nobody takes them seriously. “November is hard for everyone.” That is true, and precisely for that reason it is misleading, because there is a considerable difference between being a bit short-tempered in November and barely functioning for three months.

What seasonal affective disorder actually is

The name is slightly unfortunate, because it sounds like a disease of its own. In the diagnostic manuals it is not: it is listed as a seasonal pattern, that is, as a note attached to a depressive episode. It means the episodes recur at the same time of year for at least two consecutive years, and that outside that season there are no episodes.

The syndrome was first described in 1984 by Norman Rosenthal and colleagues at the American National Institute of Mental Health. They described a group of people who sank into depression every winter and recovered by themselves in spring, and reported that exposure to bright artificial light helped. That first paper set out almost everything we still discuss today — including the parts that later turned out to be more complicated than they looked.

What matters is that this is not a mild version of depression. When the criteria are met it is a genuine depressive episode, with everything that goes with it. I have described the difference between that and an ordinary drop in mood in my piece on why depression is not sadness.

Light is not illumination, it is a signal

The most useful shift in understanding is this: for the body, light is not primarily a means of seeing. It is a means of knowing what time it is and what season it is.

In the retina we have particular cells that do not serve vision but measure light. Their signal travels straight to a tiny nucleus in the hypothalamus called the suprachiasmatic nucleus — the internal clock. Using that information the clock sets when melatonin will be released, when cortisol will peak, when body temperature will be lowest. In winter, when morning light is scarcer and arrives later, that schedule shifts in some people. In the morning the body is still in biological night, even though the alarm has already gone off.

Why November, and why it eases in March

People often expect December to be the worst, when the day is shortest. In practice November and January are frequently worse. November because that is when the change is fastest — the body has not adjusted yet. January because the festivities stop, the days are still short and spring is nowhere in sight.

March brings not only more light but different light: morning light, strong, at the hour when it is most useful to the internal clock. That is why many people find their mood lifts within a few weeks without doing anything. It is also a trap, because every spring a person decides it will not be so bad next time, and every autumn discovers that it is.

The symptoms run the opposite way to what you expect

The classic picture of depression includes insomnia and loss of appetite. With a seasonal pattern it is often the reverse. People sleep nine or ten hours and are still tired. Appetite does not fall but rises, and specifically so — for bread, pasta, sweet things. Weight goes up in winter and down in spring.

This is not a lack of discipline. Carbohydrate craving is so consistent in this picture that it was already listed as a sign in the first description of the syndrome. One explanation is that carbohydrate-rich foods indirectly increase the availability of tryptophan in the brain, the building block for serotonin. The explanation is plausible and not definitively confirmed — I have written about why explanations through neurotransmitters are so attractive and so unreliable in my piece on the myth of chemical imbalance.

It is also interesting what does not change as much as you would expect. Many people keep the capacity to hold down a job and look after a family through the winter. What goes first is everything that is not compulsory: seeing friends, hobbies, exercise, plans. So people tell themselves everything is fine — after all, they are still going to work. What collapses from the outside is only the part nobody measures.

Another common sign is a sensation of heaviness in the arms and legs, which the literature calls leaden paralysis. People describe it exactly that way: like walking through water.

How much light you actually get in winter

Here is the biggest surprise for most people. We are convinced the office is bright. With a light meter it is not.

Light therapy: what we know

The standard is a 10,000 lux device, half an hour in the morning as soon as possible after waking, at a distance of roughly half a metre, looking past the device rather than into it. A 2005 meta-analysis found an effect in seasonal depression comparable to that of antidepressants in similar studies.

What people often overlook is the timing. With this method the hour is not a detail but the whole point — light in the morning moves the clock forward, light in the evening moves it back. Using it at the wrong time can worsen sleep rather than repair it. If your sleep is already falling apart, I have written about the mechanisms in my piece on insomnia and the nervous system.

The device is not suitable for everyone. With retinal disease, with certain medications that increase sensitivity to light, and with bipolar disorder, where it can trigger a switch into elevated mood, it is worth speaking to a doctor first. A sun in a box is still an intervention in biology.

In practice people abandon the device for entirely non-medical reasons: because it stands in a room they never enter in the morning, because half an undisturbed hour at breakfast with small children is fiction, or because they bought it in January when it was already late for that winter. If you decide to try one, first agree with yourself where it will stand and what you will do beside it — breakfast, email, reading. A device you have to go looking for does not get used.

Why talking therapy is not second division here

Because the explanation is so neatly biological, it seems logical that the solution must be biological too. The data do not confirm that so simply. Kelly Rohan and colleagues compared cognitive behavioural therapy adapted specifically for winter depression with light therapy. In the first winter the two approaches were roughly equally effective. Two winters later, however, the group that had received therapy was doing better: fewer recurrences and a milder course.

The explanation makes sense. A device works for as long as you use it. Therapy changes what you build around winter: the pattern of cancelling arrangements, the thought that “winter is a write-off anyway”, the withdrawal that starts in October and lasts until March. In the work I do, most of what happens takes place exactly there — not in a discussion about light, but in the question of how much a person hands over to winter because they believe they must.

It often turns out that winter has become a kind of exemption from a person’s own life. Relationships wait, conversations wait, decisions wait. Then in March everything returns at once, along with the sense of having missed four months. That feeling is not caused by light. It is caused by an agreement the person made with themselves in October.

Where this story does not hold

Now the honest side. The story of winter and light is neat, tidy and at least partly contested.

In 2016 a group of researchers tested the seasonal pattern in a large American sample of more than thirty thousand people and did not find the expected relationship between depressive symptoms and season, latitude or sunlight exposure. If the link were as strong as we usually assume, it should have shown up in a sample like that. It did not.

This does not mean people invent winter distress. It probably means two things: that there are fewer seasonally sensitive people than we thought, and that the differences among them are larger. Prevalence estimates vary greatly between studies, which is in itself a sign that the criteria are not solid. Part of the discrepancy also comes from the fact that seasonality is often established with retrospective self-report questionnaires, and we all like to arrange our past moods into a convincing story.

And one more thing: if every winter is worse for you, that is not necessarily a seasonal pattern. Other factors also cluster in winter — less movement, more alcohol, anniversaries of losses, family holidays, end-of-year work pressure, vitamin D deficiency, thyroid disease that can appear at any time. Before attributing everything to light it makes sense to check your blood work and talk to a doctor — I have described when that step comes first in my piece on when to see a doctor first.

What I do before winter arrives

With people who know they get this every year, I prefer to talk in September rather than January. There is still enough momentum then to set something up.

The most reliable thing is morning light, not evening light. Fifteen to thirty minutes outdoors within the first hour or two of waking, even when it is overcast and even if it is only the walk to the shop. The second is a steady waking time — more important than bedtime, because waking sets the clock’s reference point. The third is filling December and January in advance with small things already arranged, rather than things you will “sort out when you feel like it”, because you will not feel like it.

And a fourth, less popular one: write down in advance how you will know this is no longer just winter. If thoughts appear that it would not matter if you were not here, that is no longer a question of light and not something to be put off until March.

What to remember

A seasonal pattern of depression is not a disease of its own but the way depressive episodes arrange themselves across the year in some people. When the criteria are met it is a genuine episode, not a bad mood. The picture is often the reverse of the classic one: too much sleep, increased appetite, carbohydrate craving and a sense of lead in the limbs.

The best supported explanation concerns morning light and the internal clock rather than the amount of light in general, which is why light in the first hours of the day matters most. Light therapy has research support but depends on correct timing and is not for everyone; talking therapy makes at least as much long-term sense, because it also addresses what we build around winter.

At the same time it is worth staying modest: large studies do not confirm the seasonal link as clearly as one would expect, which suggests the phenomenon is narrower and more individual. If the same thing repeats every year, prepare in September rather than January — and if thoughts of death appear, do not wait for spring.