Why do we suffer from Seasonal Affective Disorder (SAD)?

Hello there! I hope you’re well and getting into the swing of your light routine? Finally, here is instalment number two of my ‘who, why, what, where, when and how’ of Seasonal Affective Disorder (SAD) and Winter Blues. It’s another long one, but I hope you’ll find it interesting! 😀

In this post I’ll be covering a couple of the accepted theories of why people get SAD and Winter Blues / Winter Depression. This is my own understanding, based on what I’ve read over the years and a little background reading I’ve done for this post. It’s taken me quite a while to write, as I keep changing my mind what to put in! I don’t want to overwhelm you with too much info, but wanted to give you enough too. As always, do let me know what you think?

Do we actually know what causes SAD and Winter Blues?

In short, no. The first thing to say is that nobody seems to really know what causes SAD and Winter Blues! There’s a lot of theories, but it’s likely that there’s a complex interplay of factors that determine whether an individual develops SAD or not.

The most commonly held theory is that a lack of exposure to daylight in the late autumn to early spring months affects the brain’s production of the hormone melatonin and the neurotransmitter serotonin.

The body has an internal body clock, known as the circadian rhythm. It regulates sleep/wake cycles, appetite, digestion, mood and many other functions. This explains why SAD affects us in so many different ways.

What we have to remember is that we are animals and in evolutionary terms our bodies haven’t caught up with the lifestyles we’ve adopted as humans. Before we learned to artificially light our homes, people went to bed when it became dark and woke when the sun rose. They also spent a lot more time outdoors and had more physical jobs.

 

SAD and melatonin

The brain responds to decreased light by increasing production of the hormone melatonin, which signals to the body that it’s time to sleep. In the morning, when light reaches the eyes, melatonin levels begin to decrease and the hormone cortisol is released. This gives us the get-up-and-go that we need to start the day.

Red traditional alarm clock - these can be difficult for SAD sufferersIn the depths of winter, when many of us need to get up while it’s still dark, the body hasn’t received the correct signals to wake up. This is why it can be a real wrench to get up and you may feel shocked out of sleep by a traditional alarm clock – your body simply isn’t ready to be awake! When you think about it, this way of waking is likely to activate your fight or flight response. You wake up stressed before you’ve even started your day! A dawn simulator can help with this, waking you up in a more natural way.

But the problem isn’t only to do with waking. On very dull days, your levels of melatonin can stay high throughout the day, leading to those feelings of lethargy and sleepiness that you might recognise all-too-well. Before I was diagnosed with SAD, I would return from college and want to go straight to bed – I couldn’t keep my eyes open!

SAD and serotonin

The neurotransmitter, serotonin, is also thought to have a key role to play in SAD, as it appears to in other types of depression. Researchers have found that levels of serotonin can vary from day-to-day and across the year, with levels markedly lower in winter. People with lower levels of serotonin appear to be more likely to experience symptoms of all kinds of depression.

Reading about how to increase serotonin in the human brain without drugs (Dr. Simon N. Young, 2007), this theory makes sense to me. If you’re anything like me, in winter you’ll be less likely to go outside at lunchtime, or whenever. Often eating at my desk means I move my bones less, get less natural light and I’m probably eating stodge, too. Carb cravings are a common symptom. I mean – who really fancies a salad in the middle of winter? Certainly not me! Haha – yes, yes, I’m aware that I don’t always follow my own advice! 😀

So, if light, exercise and a healthy diet are major natural ways of increasing serotonin production, then it would seem to follow that not doing/having these things may cause you to feel rubbish. At least, that’s how I understand it! 

Some further reading

As always, if you haven’t already, I’d recommend you have a look at the following excellent articles about SAD. They explain a bit more of the why in more medical terms than I have done:
NHS
Mind

If you’re interested in doing a bit more digging around into theory, here’s a few other theories that caught my eye:

People who suffer from SAD have an ‘unhelpful’ way of controlling serotonin –
Seasonal difference in brain serotonin transporter binding predicts symptom severity in patients with Seasonal Affective Disorder – Mahon et al (2014)

People who suffer from SAD may have retinal sensitivity anomalies –
Evidence of a Biological Effect of Light Therapy on the Retina of Patients with Seasonal Affective Disorder – Marie-Pier Lavoie,Raymond W. Lam,Guylain Bouchard,Alexandre Sasseville,Marie-Claude Charron,Anne-Marie Gagné,Philippe Tremblay,Marie-Josée Filteau,Marc Hébert (2009), Biological Psychiatry, Elsevier

People who suffer from SAD have lower levels of cortisol production in winter –
Seasonal differences in the diurnal pattern of cortisol secretion in healthy participants and those with self-assessed seasonal affective disorder – Thorn, Lisa and Evans, Philip D. and Cannon, Anne and Hucklebridge, Frank and Clow, Angela (2011), Psychoneuroendocrinology

An ongoing debate…

There’s a lot of debate still ongoing, though, as many of the theories don’t give absolute or satisfactory answers. So for example, suppressing melatonin doesn’t ‘cure’ SAD. Anti-depressants don’t work for everybody. Light therapy works for around 85% of people. It really does seem that individual differences can play a big part. So you may be more at risk of developing SAD if you or your family have a history of depression, or if you’ve been under chronic or sudden stress. If you suffer from depression that isn’t seasonal, it can feel worse in the winter.

Having said that, there does seem to be strong evidence to support the theories surrounding melatonin and serotonin having a key role to play. Correspondingly, there’s also strong evidence to support light therapy. If you want to do some more reading still, have a look at Lumie’s page of research abstracts. SADA members also receive monthly e-bulletins and longer newsletters three times per year which contain scientific news on SAD and Winter Blues.

I hope that this will have been a helpful post for you. Do you think there’s anything I need to add? What other theories have you read?

Take care,

– Neens –

Image credit
Alarm clock: http://www.freeimages.com/photo/alarm-clock-1621256

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