For some people, winter is literally depressing. In ‘Chasing the Sun’ Linda Geddes shows how we first came to recognise seasonal affective disorder (SAD) thanks to one enthusiastic mood diarist, and looks at how we might treat the condition.
The modern story of SAD as a syndrome dates to the late seventies, when a team of researchers at the National Institute of Mental Health (NIMH) in Maryland, who had been investigating how light affects biological rhythms, were approached by Herb Kern, a short, 63-year-old engineer with a crew cut.
Brimming with energy and enthusiasm, Kern had been keeping detailed records of his bipolar mood swings since 1967, and was convinced that they showed a seasonal pattern, which related to the length and intensity of sunlight. To try to validate his theory, Kern had joined the American Society of Photobiology and had already spoken with several researchers in the field about his mood swings.
Two NIMH investigators, Alfred Lewy and Sanford Markey, had recently published a report on a new method of measuring melatonin levels in human blood plasma: Kern wanted them to test his blood during spring and winter, to see if they could identify biological differences that might account for his changing moods.
Lewy and his colleagues already knew that day length dictated seasonal changes in the biology of certain animals, and that it was the duration of melatonin secretion (that biological beacon of the night) that told their bodies what time of year it was. They had also just demonstrated that melatonin secretion could be suppressed in humans if they were exposed to bright light.
Each morning, between 6am and 9am, he would be bathed in bright white light.
The researchers came back to Kern with a proposition of their own: if the long winter nights really were flooding his system with melatonin and contributing to his depressed mood, then shortening the duration of melatonin secretion, by exposing him to bright light during the morning and late afternoon, should lift him out of it.
Kern agreed to be their guinea pig, and so the following winter – during his annual low – he became the first human to undergo a course of treatment with a light box. Each morning, between 6am and 9am, he would be bathed in bright white light – just as if he’d flung open the curtains to reveal a clear spring morning. This process was repeated at 4pm, when the streets outside were already darkening. After three to four days of this, Kern’s mood began to lift; and by the tenth day he was better.
The birth of syndrome
Curious to know how many other people suffered from this strange seasonal illness, another of the researchers, Norman Rosenthal, contacted a reporter at the Washington Post, who wrote a story about it. The public response was overwhelming: thousands wrote in, providing a ready cohort of self-selected candidates on which to conduct further experiments with light.
Rosenthal was, himself, sympathetic to their struggles. A native of South Africa, he had arrived in the US in 1976, and quickly experienced a sensation that he’d never encountered before: a draining of energy and a difficulty in achieving all his tasks once the days drew short and dark. As the snow melted, he’d notice his energy returning and wonder what all the fuss had been about those past three months.
At the time, the only explanation anyone could give came from his own psychiatric patients, who’d say things like: “Do you know, everybody in the office has the ‘Christmas Crunch’ and they’re all having difficulties.”
Rosenthal came up with a new label for this seasonal lethargy and depression: seasonal affective disorder. And so a syndrome was born.
In 1984, he published a paper describing 29 patients – 27 of whom had bipolar disorder – reporting a history of depressive symptoms in winter that disappeared during spring and summer. Again, there was an enormous public response: “It was as though this something had been there all the time, but it didn’t have a diagnosis or label until then,” recalls Anna Wirz-Justice, an emeritus professor of psychiatric neurobiology at the University of Basel, who worked at NIMH at the time.
SAD was formally recognised by the American Psychiatric Association in 1987, although today most psychiatrists regard it as a subclass of general depression or bipolar disorder. In both conditions, some 10 to 20 per cent of patients report a seasonal variation in their symptoms, but the depression associated with SAD does have some unusual characteristics.
Whereas people with general depression often lose their appetite and suffer from insomnia, people with SAD often oversleep and overeat (craving carbohydrates is particularly common). Also, the onset of SAD symptoms is usually triggered by shortened daylight exposure as opposed to negative life events.
Who gets SAD?
Statistics on the prevalence of SAD vary depending on the method used to diagnose it, but most studies have used a tool called the Seasonal Pattern Assessment Questionnaire (SPAQ), which assesses seasonal variations in mood, energy, social contact, sleep, appetite and weight. Using these criteria, up to 3 per cent of Europeans, 10 per cent of North Americans and 1 per cent of Asians suffer from SAD.
Women seem to be more affected than men, and people who migrate from lower to higher latitudes also seem to be more susceptible. As you might expect, SAD prevalence varies significantly with latitude. One US study found a prevalence of 9.4 per cent in northerly New Hampshire, 4.7 per cent and 6.3 per cent in New York and Maryland respectively, and just 4 per cent in the balmy southern state of Florida.
Many more people experience a milder form of the condition called sub-syndromal SAD, or the winter blues. In the UK, one in five people claim to experience the winter blues, but only 2 per cent suffer from true SAD. However, estimating the true prevalence is difficult, given the subjective nature of symptoms such as mood and lethargy.
That said, there are measurable differences in brain chemistry across the seasons. For instance, brain levels of the mood-regulating neurotransmitter serotonin are highest in summer and lowest in winter in all of us – while availability of the amino acid L-tryptophan, which is needed to synthesise serotonin, fluctuates as well.
The causes of Seasonal Affective Disorder
So, what could be responsible for triggering such changes? There are several theories, none of them definitive. One idea is that people may have retained the same biological mechanism that certain other mammals, like sheep, use to keep track of the seasons. The animals’ bodies respond to changes in the duration of melatonin secretion at night. From an evolutionary perspective, it could have made sense to become more lethargic and depressed during the colder months as a means of conserving energy when food would have been less plentiful.
Another theory is that people with SAD are less responsive to light, so that once light levels fall below a certain threshold – particularly if sufferers are spending a lot of time indoors – they struggle to synchronise their circadian clocks with the outside world.
We tend to wake up grumpy and become more cheerful as the hours pass, then our mood falls again overnight.
However, the leading theory is the “phase-shift hypothesis”: the idea that later sunrises in winter delay our internal rhythms so that they’re no longer in tune with when we go to sleep and wake up. Exposure to artificial light at night could delay us even further. Most people’s moods follow a strong circadian rhythm: we tend to wake up grumpy and become more cheerful as the hours pass, then our mood falls again overnight. If this pattern were to become misaligned with the actual time of day, then those lows in mood might occur during the daytime instead. If our bodies were still in ‘night mode’ when we woke up, we might also feel more tired and sluggish – another common symptom of SAD.
Learning from the Sami
The traditional inhabitants of the far north, the Sami people, embrace the differences between the seasons, rather than trying to maintain the same pattern of activities and behaviour year-round. Ken Even Berg is a Sami guide in his late twenties who grew up in the village of Karasjok, some 300 km east of Tromsø, near the border with northern Finland.
For most of his life, he has led a traditional, semi-nomadic lifestyle, following the reindeer herd from their winter feeding grounds near Karasjok to their summer grazing near the coast. This takes around ten days in the spring, and ten weeks in autumn, during which time the herders sleep in tents and follow the reindeer on quad bikes. “For the Sami, it’s not so much about light and dark, as when the reindeer are moving,” he says. Because reindeer have no circadian rhythm, this can occur at any time of day or night: “They move a little bit, then they eat a little bit, then they sleep a little bit,” he says.
And so the Sami live by the seasons. In spring they often sleep during the daytime, because the snow gets slushy, making it harder for the reindeer to move. At night the ground is rock-hard, and so that’s when most travelling occurs. Summer is a time for chores, such as maintaining fences, and checking that the new calves are okay.
It’s also the season when people are at their most sociable and lively. September is the period for rounding up the calves and taking some of them to market; then it’s time to begin the migration back east, which gets harder as the days grow shorter. (Autumn also sounds like a fun time for the reindeer, when they feast on hallucinogenic mushrooms and stagger around like drunk teenagers.)
Winter is a slower time, when the reindeer herders are back in the family home, and the long dark nights make everyone sluggish and less sociable: “I just don’t feel like going out and meeting people in winter, so I stay at home,” Berg says. This fluctuation in seasonal patterns, and annual winter slow-down, is long accepted as part of the Sami’s traditional way of life.
Using CBT to combat SAD
So, could adopting a more positive, accepting attitude to winter help others who suffer from SAD or the winter blues? Kelly Rohan, a professor of psychology at the University of Vermont, is convinced it might. She has recently published several trials comparing cognitive behavioural therapy (CBT) to light therapy in the treatment of SAD, and found that the two were roughly comparable during the first year of treatment.
Longer term, CBT was even more effective than light. By addressing people’s attitudes towards winter, rather than just focusing on their symptoms, CBT breaks the patterns of negative thinking. In the case of SAD, that could be rephrasing thoughts such as: “I hate winter” to “I prefer summer to winter”, or “I can’t do anything in winter” to “it’s harder for me to do things in winter, but if I plan and put in effort I can”, Rohan explains. “I don’t argue that there’s a strong physiological component to SAD, and it’s certainly tied to the light-dark cycle,” she says. “But I do argue that the person has some control over how they respond to and cope with that. You can change your thinking and behaviour to feel a bit better at this time of year.”
Finding things to look forward to in winter – be it saunas and ice swimming, or simply cosying down in front of the fire with a good book – could therefore be an effective way of addressing winter blues. And if you can identify enjoyable winter activities that will get you outdoors to reap the alerting, mood-boosting effect of bright daylight, so much the better.
About the author
Linda Geddes is a science journalist who specialises in biology, medicine and technology. She has worked as both an editor and reporter for New Scientist magazine, and has received numerous awards for her journalism, including the Association of British Science Writers’ award for Best Investigative Journalism. She is also the author of ‘Bumpology: The Myth-Busting Pregnancy Book for Curious Parents-To-Be’.
Most recently, she is the author of Chasing the Sun: The new science of sunlight and how it shapes our bodies and minds, published by Wellcome Collection.
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