Examining the science behind the winter blues

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TORONTO — As winter approaches, many people will notice a change in their mood. In fact, seasonal changes in mood and behavior have been shown to occur in just about all of us.

On one end of that spectrum is what we call Seasonal Affective Disorder, or SAD, which refers to a mood disorder such as depression or bipolar disease which occurs in a seasonal pattern.

This affects six to 10 percent of North Americans, while a milder and more common form called Subsyndromal SAD, which doesn’t meet the medical criteria for depression, can affect up to 20 per cent of us.

READ MORE: Tips for staying active, healthy and beating the winter blues

The typical symptoms of SAD are sleepiness, increased appetite and particularly cravings for carbs, and weight gain.

People also describe feeling like their arms and legs are heavy and hard to move (“leaden”) and that they’re often more sensitive and irritable.

So why does this happen?

Studies suggest that it has to do with the impact of light on our bodies.

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READ MORE: Light therapy benefits for non-seasonal depression as well: study

The decrease in the number of daylight hours in the fall and winter causes the brain’s biological clock to fall out of sync with the solar cycle.

This decreases brain levels of serotonin, which regulates mood, appetite, and sleep.

It also causes melatonin, which controls our sleep-wake cycle, to be produced and release at the wrong times.

This relationship with light explains why SAD is more common in countries at higher latitudes.

In addition, studies have found genetic factors which might explain why this affects some people more than others.

That being said, it’s not yet clear whether SAD is inherited as a distinct disease, or whether sensitivity to season change and depression are each inherited as separate traits, and happen to coincide in certain people.

READ MORE: Change in season causing Seasonal Affective Disorder for many

The good news is that the treatment is as simple as the cause. Since a lack of daylight causes the imbalance, exposure to light can correct it.

For milder symptoms, that might simply mean more outdoor activity and exercise, particularly on sunny days.

For full-blown SAD, most people respond to light therapy.

This involves sitting in front of a powerful light source for 30 to 45 minutes once or twice a day, or using a special morning light that simulates the dawn (a high-intensity fluorescent lighting system, tilted downward toward the head).

A review of 13 randomized controlled trials comparing light therapy to a placebo therapy (red, yellow, or white light), showed significant improvements in SAD patients’ depressive symptoms with light therapy.

Typically, the light is between 2,500 and 10,000 lux in intensity. For perspective, typical living room lighting is 50 lux, office lighting is 500 lux, and direct sunlight is up to 100,000 lux.

Such lights are readily available online for about $100.

If light therapy is ineffective or incompletely effective, other therapies can be used.

Randomized trials have found that antidepressants including fluoxetine and moclobemide are beneficial in SAD, and cognitive-behavioral therapy (a type of psychotherapy) can also be used.

So there’s a lot more to those winter blues than you might have thought.

If you are feeling down, you’re not alone, and a few simple strategies can make things better, so make sure you talk to your doctor and ask for help.