The fact is, that SAD is real condition, and it affects 20% of us mildly and 2% of us very badly. It's a type of depression that is affected most by seasonal conditions, and winter - obviously - is when it is at its worst.
For the 20% of us who are pre-disposed to it, it tends to be a feeling of low moods, which some of us call winter blues. But for the other 2%, says the Seasonal Affective Disorder Association (SADA), it can stop you from functioning properly.
According to BUPA, SAD most affects people between 18 - 30, and it most commonly affects women.
"SAD or Seasonal Affective Disorder or 'winter blues' is a real condition," says Dr Raj Persaud, consultant psychiatrist, talking to HuffPost UK Lifestyle, "but only recently recognised by modern medicine. The key is to get the diagnosis right and it is often misdiagnosed. It's not just that you should feel significantly depressed during winter over several years (and this low mood should be accompanied by other body changes such as sleeping and eating more than usual during this time), but you should actually feel 'better than well' in the summer.
"However, just because you may not suffer from the full blown syndrome, doesn't mean you may not be experiencing from a milder form of the condition."
It isn't clear why certain people suffer from SAD and others don't, but it is thought that it may be due the lack of sunlight and the effect this has on chemicals in the brain.
BUPA suggests the theory that serotonin, the chemical our body produces to make us feel good, may be much lower in people with SAD in winter. The NHS adds that "In people with SAD, a lack of sunlight and a problem with certain brain chemicals stops the hypothalamus working properly. The lack of light is thought to affect the production of the hormone melatonin and the body's circadian rhythm (the body's internal clock, which regulates several biological processes during a 24-hour period."
Here are the symptoms below - and be warned - these can sound similar to how a lot of people feel during winter. What you're looking for is a distinct shift, and a lack of ability to mobilise.
If you do suffer from SAD, your GP will be able to diagnose it with an assessment.
Treatments range from light therapy to talking therapies and in more severe cases, anti-depressants.
"The treatment is in fact very effective," says Dr Persaud, "and often involves more exposure to high intensity light during the winter. This can be achieved by the purchase of a light box, as normal in-door lighting usually isn't intense enough. As these boxes can be quite expensive - going for a walk outside daily of at least an hour's duration may achieve the same result.
"It may not be obvious but going outside even on a cloudy winter's day achieves as much light exposure as needed as long as you are outdoors for long enough. It now appears that the timing of the light exposure might be crucial - getting exposed to high intensity light at the beginning, or the end of the day, might be particularly therapeutic. This might be because this tricks the brain into thinking the shorter days of winter have been replaced by the longer days of summer."
Lumie.com is one of our favourite websites for light therapy boxes and Bodyclock alarms.
Oily fish is the best source of the essential fats found in high concentrations in the brain. The higher your level of these omega-3 fats, the higher your level of the happiness hormone serotonin is likely to be. Eating oily fish also lowers your risk of heart disease, and gives you velvety skin and better concentration.
We have more bacteria in the gut than cells in our entire body, and they are vital for proper immunity. They also affect our mood. When you go into a state of stress, hormones communicate this to the gut, which shuts down digestion and promotes inflammation.
This can manifest as anything from a headache to an aching joint or gut pain. Probiotics (good bacteria) calm inflammation in the gut and also signal to the brain to calm down. It’s important to take the correct ‘human strains’ of probiotics identical to those inside us. The two essential types are Lactobacillus acidophilus and bifidobacteria. The most effective way to restore a healthy balance is to take supplements that feed existing healthy bacteria, such as Bimuno's Prebiotic powder, £9.99, available from Boots.
Music will help you
Anything that helps you switch off adrenalin will help you get to sleep more easily. Avoiding caffeine is a no-brainer, but you can do more by boosting the neurotransmitter GABA, a natural antidote to anxiety. In the EU, GABA supplements are only available on prescription, but there are other ways to increase it. Valerian, sometimes referred to as ‘nature’s Valium’, is the most potent GABA-promoting herb and it works well for many people. To help you sleep, take 150mg-300mg about 45 minutes before bed. Music can also help you switch off by shifting the brainwave patterns to alpha waves, associated with deep relaxation.
Go out to ward off the winter blues
Serotonin levels are lowest in winter, as the amount we produce is linked to how much sun we’re exposed to. Some people are prone to low serotonin anyway, and a lack of light can tip them into depression. But there’s another reason, and that is lack of vitamin D. This mood-boosting vitamin relies on sunlight on the skin.
So, how do you get more winter light? One way is to spend more time outdoors. And if you combine exercise with sunlight exposure, that’s all the better. Only 5% of the rays that make vitamin D get through glass so, when you can, exercise outdoors for 30 minutes a day. Supplement with Better You Vit D Spray, £6.25.