With the clocks going back, millions of British workers will be heading home this evening in the dark. Depressing? Yes, but there could be a good reason for why we get the winter blues.
When Jenny Simmonds had her first bout of SAD 20 years ago, the doctors said it was postnatal depression. But then her spirits slumped again the following winter.
"She was depressed two years after the birth," says husband Jon. "I'm no doctor, but I thought, 'this isn't postnatal'. It happened again the next year, and the next. For 10 years we were told it was a chemical imbalance."
Eventually, the couple heard about seasonal affective disorder. Jenny got a name for her condition, and began looking for ways to deal with it, that didn't involve an annual sojourn at her local hospital.
Seasonal affective disorder, or SAD, is now a recognised psychiatric condition. Miserable weather, a bunged up nose every two weeks, not forgetting a seasonal rise in household burglaries, well, it's hardly a recipe for fun,
And what the dark days do is mess with the balance of chemicals that affect a person's moods.
The lack of decent daylight leads to a drop in the body's levels of serotonin and a rise in melatonin. Put bluntly, serotonin makes us livelier, melatonin makes us sleepy.
"How do birds know when to leave the country?" asks Jon Simmonds. "In the autumn, trees change colour, animals hibernate, yet we're expected
to carry on as normal!"
It's estimated that 3% of UK adults suffer SAD to a clinically significant degree. Some of those will be affected to such an extent that
going to hospital is the only option. A further 10% will endure milder symptoms.
It all adds up to millions of Brits spending dark, moody months suffering loss of libido, anxiety, irritability and social withdrawal. But what must it be like for those who live even further north, where winter days are even shorter? Surprisingly, it's not nearly so bad.
Countries such as Iceland or Finland, which are endowed with snow and have little history of mass immigration, may not get many hours of sunlight, but chances are they'll get clear skies and plenty of light reflecting off the snow.
It helps explain why British folk find rejuvenation not only in winter holidays to far-flung sun-drenched beaches, but also from visiting a frosty mountain top for a week's skiing.
The rejuvenating effect of snow
And the immigration? One theory goes that it's all about genetic build, natural resistance developed over the centuries. Once immigrants arrive from lands closer to the equator, not used to dealing with seasonal drops in sunlight, the resistance weakens, and the winter misery rises.
Dr John Eagles, from Royal Cornhill Hospital Aberdeen believes evolution may also play its part. One indicator of this is that women of a child-bearing age are statistically at the highest risk of SAD.
In a recent paper on the condition, the consultant psychiatrist writes, "At one stage, it may have been advantageous to have been energetic and to require little sleep in the summer and to be anergic and sleepy in winter.
How to beat SAD
"This may have applied especially to women and their offspring, since it would be optimal to become pregnant in summer, resulting in childbirth in spring, when food is more plentiful and the weather is becoming warmer."
So if you've got the winter blues, and your boss will neither sanction, nor finance, your three-month break in the sun, what options are available?
At least she'll be going home in the light
For mild symptoms, exercise is a key recommendation along with a decent diet. That means trying not to over indulge those chocolate urges. But if you must, go for dark chocolate.
An increasingly popular option is to sit in front of a lightbox for an hour or so a day.
"I thought light therapy was the biggest load of cobblers", says a once sceptical Jon Simmons. "My wife used it over one winter period and didn't become ill. I thought that was psychosomatic.
"When it helped the next winter too, I thought, well, maybe it works!"
Cambridge-based company Outside In has been selling lightboxes since 1991.
"Treatment plan A is to move to the south of Spain," says founder and MD Steve Hayes. "Plan B is to introduce artificial light, when nature isn't providing. That sends a signal to part of the brain saying it's daytime now. The natural response is to stop producing melatonin and increase serotonin
Steve says demand for the lights is pretty consistent across the UK, the one possible exception being Aberdeen where sales are "extraordinarily big".
"It's north, it's cloudy and it's full of Texans who can't believe what's hit them!"