Dark nights getting you down? You may be suffering from SAD syndrome - Seasonal Affective Disorder. An estimated two million people in the UK are hit by SAD syndrome from November to March - symptoms are grumpiness, fatigue and feeling down.
What many don't realise is the part that sugar plays in SAD syndrome - and how even a little bit of exercise can make a big difference.
Here's what's going on inside us: our bodies produce a natural "happy drug" called serotonin, a hormone which makes us cheerful and lively. During the summer, daylight triggers serotonin, as does exercise.
So on a warm sunny evening that's why we come home from walking the dog (or the husband) and feel great! As winter draws on, it all this changes.
Look how daylight varies through the year: May 15 hours, July 16 hours+, September 14 hours - but in December and January we see barely eight hours. Classic SAD syndrome conditions.
Now here's where it all goes pear-shaped in winter (and so do we if we're not careful).
Because there's so much less daylight to stimulate the release of serotonin, and because we feel much less inclined to exercise in the dark, we need to get our fix of the happy drug from somewhere else.
Guess what else produces great bursts of serotonin? Sugar! So a doughnut or a bar of chocolate can make us feel good, too. That's why many of us get cravings in the winter.
But there's a big difference in the happy hit we get from sugar - it doesn't last long.
That's because the sugar also stimulates the release of another hormone called insulin, which is designed to help drive sugar out of the blood and into cells, where it can be use to produce energy.
What happens then is that the insulin then drives down the blood sugar level and can produce low blood sugar, what doctors call "reactive hypoglycemia."
The symptoms are fatigue, irritability, depression (SAD syndrome in fact) - plus more sugar cravings. So someone with SAD syndrome often reaches for sugar again for another quick fix.
You can see that they're caught in a particularly vicious cycle. The research on how what we eat affects our mood is overwhelming.
Is there any way out of SAD syndrome? Happily, there is. Research shows that eating a balanced diet, getting some exercise and cutting down on caffeine can fight the effects of SAD syndrome.
Serotonin can be found in a variety of foods. The highest concentrations are found in walnuts, plantains, pineapples, bananas, kiwis, plums and tomatoes.
Studies have shown that ingesting carbohydrates boosts serotonin synthesis and levels because they contain the essential amino acid tryptophan, which is used by the brain to produce serotonin.
Particularly tryptophan-rich foods include turkey, bananas, milk, yoghurt, eggs, meat, nuts, pineapples, plums, beans, fish, and a variety of cheeses including Swiss and Cheddar.
In numerous studies exercise has been shown to increase serotonin production and release. In particular, aerobic exercises, like running and biking, are the most likely to boost serotonin. However, yoga works too.
Interestingly, if you try to do too much exercise, or feel forced into doing it, it may not have the right effect. Recognising that you're choosing to exercise alters its neurochemical effect.
Make exercise an essential part of your routine. The biggest problem with exercise is that when people don't feel like doing it, they don't do it.
But sometimes the reason they don't feel like doing it is because their serotonin activity is low, and they'd rather comfort eat junk food in front of the TV. So it's important to overcome your feelings and remember what's important to you - your wellbeing.
NHS Choices recommends that managing your stress (easier said than done with Christmas racing up on us) can play a major part in fighting SAD syndrome.
Stress makes the body release the hormone cortisol, which makes you want something that's comforting (sound familiar?).
If your brain has learnt to reach for food as a response to negative feelings - what experts call a "trigger" - this can result in craving sugary things to take away stress...and put on the pounds.
How often do we hear "I desperately need sugar because I'm tired"? Research shows that sleep deprivation plays havoc with the mind/body connection and our hormones. That's when the hunger hormone ghrelin raises its ugly head!
So make a good night's sleep a priority and during the day, grab a power nap instead of doing anything else.
Healthier choices, getting out more, being more active, sleeping well, reducing your stress...now that's a virtuous cycle guaranteed to put a smile on any face.