Seasonal affective disorder

Seasonal affective disorder is depression that follows a seasonal pattern. It arrives at roughly the same point each year, lasts for months, and lifts again. It is not a separate illness from depression, and that is the most useful thing to know about it, because it is what decides the treatment.

UK guidance is explicit: seasonal affective disorder is treated as depression is treated, with a talking therapy or an antidepressant. Light therapy — which is what almost everything written on the subject leads with — sits further down that list, on weaker evidence than its reputation suggests.

What it looks like

The core of it is the same as any depression: a low mood that persists rather than passing, loss of interest in things that normally hold it, irritability, tearfulness, low self-esteem, anxiety, reduced interest in sex, and a pulling away from other people.

Three features are more characteristic of the winter pattern specifically, and they are the ones that mislead people into thinking it is not depression at all:

• Sleeping a great deal more than usual and waking unrefreshed, rather than the broken sleep and early waking more typical of non-seasonal depression.
• Heavy, physical fatigue, along with difficulty concentrating.
• A marked craving for carbohydrates, often with weight gain — again the reverse of the appetite loss that usually accompanies depression.

Because of that, someone who is sleeping twelve hours and eating more than usual may not recognise what is happening as depression, and nor may the people around them.

What makes it seasonal rather than simply a bad winter

The pattern is the diagnosis. It is identified where depression recurs at about the same time of year across several years, with genuinely well periods in between. One difficult winter is not it. Nor is disliking winter, or feeling flat in February, which is extremely common and not an illness.

A GP will ask about mood, sleep, appetite, how much ordinary life is being affected, and whether there is a personal or family history of depression — the condition does appear to run in families. There is no test for it; the history is the evidence.

A smaller number of people have the pattern the other way round, with symptoms through the summer that ease in winter. It is less common, less well described, and treated on the same principles.

Why it happens

The cause is not settled. The leading account is that reduced daylight acts on the hypothalamus, and through it on three things: melatonin, the hormone involved in sleep, which may be produced at higher levels than usual; serotonin, which affects mood, sleep and appetite, and which may fall when there is less light; and the body clock, which daylight normally keeps aligned and which the winter light pattern may disturb.

Each of those is a plausible mechanism rather than a demonstrated one, which is worth knowing when reading confident explanations of how a particular product works.

Treatment, in the order the evidence puts it

Talking therapy. Cognitive behavioural therapy has the strongest evidence base of the talking therapies for depression and is the usual first offer. In England it can be reached without a GP appointment and without a diagnosis, by referring directly to NHS talking therapies; elsewhere in the UK the route is through a GP. Mental health sets out both, and the first therapy session covers what the first appointment involves.

Antidepressants. Used where symptoms are more severe. SSRIs are the usual choice. The evidence specific to seasonal affective disorder is limited, and the practical point is about timing: where the pattern is well established, starting at the beginning of the season and continuing into spring is thought to work better than starting once the depression has taken hold. They take four to six weeks to have a full effect, and are not stopped without medical advice.

Light therapy. Sitting near a light box for thirty to sixty minutes each morning. The evidence is genuinely mixed — NICE's position is that it is unclear whether it works, and the benefits found in trials have mostly been short-term — which is why it is not usually provided on the NHS. A good many people nonetheless find it helps them, and it is reasonable to try. It is simply not the first thing to try, and it is not a reason to delay the two above.

Light boxes, for anyone buying one

Since these are bought privately rather than supplied, nobody is checking the claims on the packaging, so a few specifics are worth having.

Ten thousand lux is the usual specification. The box is used in the morning, positioned off to one side with the eyes open but not looking into it, for half an hour to an hour. Where it works, the improvement generally appears within about a week rather than building over months — so a fortnight is a reasonable trial, and there is no point persisting for a season with something that is doing nothing.

Boxes made for this purpose filter out ultraviolet. Side effects are uncommon and mild: headache, eye strain, a feeling of agitation, disturbed sleep, tiredness, occasionally blurred vision.

Three things warrant a word with a GP first. Any existing eye condition. Anything being taken that increases sensitivity to light, which includes some antibiotics and other prescribed medicines, and St John's wort. And — the one that matters most — any history of periods of unusually elevated mood, racing energy or reduced need for sleep. A seasonal mood pattern that includes highs as well as lows is a different diagnosis requiring different treatment, and light therapy can make that pattern worse rather than better.

Dawn-simulating alarm clocks, which brighten gradually before waking, are a gentler version that some people get on with.

Two things that are not light therapy. A sunbed is not a treatment for anything — it delivers ultraviolet, which is what the light boxes are designed to exclude, and it carries a real risk of skin cancer. And the lamps used to treat acne, psoriasis and eczema are a separate ultraviolet treatment given under dermatological supervision; the two are not interchangeable in either direction.

Daylight, exercise and the rest

The ordinary measures are in UK guidance as part of the picture, and they are free. Getting outside in daylight, particularly in the morning — a walk at lunchtime is the most available of them, and a dull winter day outdoors is still far brighter than a lit room. Keeping working and living spaces light, and sitting near a window where there is a choice. Regular exercise, outdoors where that is possible. Telling the people close by that this happens, so the pattern is recognised rather than argued about.

All of that is worth doing. None of it treats depression that is more than mild, and taking it up is not a reason to put off an appointment.

On vitamin D, the UK advice is separate and often conflated with this. Everyone over the age of one is advised to consider a daily ten-microgram supplement through autumn and winter, because there is not enough ultraviolet in British sunlight during those months for the body to make its own. That is advice about bones and muscles. It is not a treatment for seasonal affective disorder and should not be taken as one.

One correction worth making

It is widely repeated that depression and suicide rise over the Christmas period. They do not. The winter holiday months are consistently among those with the lowest daily suicide rates in the year, and the higher rates fall in spring and early summer. The claim has been tracked in news coverage for decades and is still printed every December.

The reason it matters is not pedantry. A seasonal pattern that is real — winter depression — gets attached to a date that is wrong, which encourages people to wait out December and expect to feel better in January, when the months ahead are the harder ones.

When not to wait for spring

Knowing that it will lift eventually is one of the things that makes this condition easy to endure rather than treat. Several situations are worth acting on rather than sitting out:

• Where it is interfering with work, study, sleep or relationships.
• Where this year is worse than previous years, or the onset is arriving earlier each year.
• Where the pattern is known and autumn is beginning — the point at which treatment is most effective, and the reason to raise it in October rather than January.

Depression of any pattern can bring thoughts of self-harm, or of not wanting to be alive. That is a reason to get help now rather than to wait for the season to turn. Mental health lists the crisis lines, which are open at any hour, and the routes to help that do not require a GP appointment.