More than three million Canadians will experience a major bout of depression at some point in their lives, according to the Canadian Mental Health Association. Most of them will be women and most will be between the ages of 22 and 44.

In 1998, StatsCan estimated depression cost Canadian employers more than $14 billion in lost productivity. Followup research released by Statistics Canada on Jan. 12, 2007, found that half a million Canadian workers experience depression and most of them — almost 80 per cent — say the symptoms interfere with their ability to work.

The survey found that four per cent of workers between the ages of 25 and 64 had experienced depression in the 12 months before the survey. The workers most prone to depression were those who regularly worked evening or night shifts and those employed in sales or service.

Depressed workers reported an average of 32 days in the previous year when their symptoms left them either unable to carry out normal activities or totally unable to work.

A study released by Statistics Canada on Oct. 17, 2006, found that slightly more than one million adults reported a "major depressive episode" in the year before they were interviewed. Seventy per cent of those surveyed held jobs.

In September 2008, another StatsCan report found that depression was "significantly associated" with an increased risk of heart disease among women — but not men.

However, depression is a highly treatable illness: 80 per cent of people who seek help can be successfully treated. But 15 per cent of those diagnosed with a severe depressive episode commit suicide.

I'm feeling down. Am I depressed?

Not necessarily.

It's normal not to be in the best of moods all day, every day. However, you may be depressed if you're experiencing:

• A major drop in your mood that lasts most of the day and is consistently low for two weeks or more.
• A loss of interest in things you normally love to do.
• Changes in sleep patterns.
• Loss — or increase — of appetite.
• Inability to concentrate or function at work.
• Irritability at home or at work.
• Grudges against people you perceive have wronged you.
• Decreased sex drive.
• A desire to avoid other people.
• Overwhelming feelings of sadness or grief.
• Unreasonable feelings of guilt.
• Thoughts of death or suicide.

Are there different types of depression?

There are three main types:

Major depression

• Interferes with work, study, sleep, eating habits and activities.
• Depressive episodes may strike some individuals once, but more commonly occur several times in a lifetime.
• Primary symptoms include sad, anxious or "empty" moods; hopeless feelings; a sense of guilt, worthlessness or helplessness and a loss of interest in activities.
• Fatigue or insomnia may be symptoms as are changes in sleep habits or appetite.
• Thoughts of death or suicide can suggest depression, as can physical symptoms that don't respond to treatment.
• Strikes women twice as often as men.

Dysthymia

• Dysthymia lasts longer than major depression, but is less disabling.
• A dysthymia sufferer can function although depressed feelings generally prevent the individual from functioning well or feeling good. Many people with dysthymia also experience major depressive episodes at some time.
• Characterized by a lack of enjoyment in life that normally lasts at least two years.
• Over a lifetime, dysthymia can have severe effects: high rates of suicide, poor functioning at work and social isolation.
• Strikes women twice as often as men.

Bipolar disorder

• Sometimes called manic depression.
• Least common form of depression.
• Dramatic mood swings are typical.
• Symptoms include abnormal elation, decreased need for sleep, increased sexual desire, markedly increased energy, and inappropriate social behaviour.
• Left untreated, a manic episode could worsen into a psychotic state.
• Strikes men and women equally.

What causes depression?

There is no one cause of depression. It can be triggered by a specific traumatic event in your life, a biochemical imbalance in your brain or your outlook on life, if it's particularly negative.

There can also be other factors that make some people more prone to depression than others, such as a family history of the illness.

Depression could also follow prolonged stress on the job. Judith Berg, a Vancouver-based therapist, says workplace depression can result from stressors such as high demands over which you have little control.

She says enlightened employers are looking for ways to address those issues.

"In the last five years, they've moved away from the old health promotion model into looking at what can they do in the organization to reduce the stress."

How long does depression last?

It depends on the person, the depth of the depression and the help available to the person suffering from the depression.

If left untreated, depression may lift on its own after several weeks or months. With professional treatment, it could end much more quickly.

Depression is rarely permanent. But once a person has suffered an episode of depression, they are more likely to experience it again. How is depression treated?

Those who realize they are suffering from depression benefit from professional counseling and — possibly — medication. There is a wide range of anti-depressants on the market that have been approved in the treatment of depression.

Medication does not normally "cure" depression. But it can help people get through their daily routines.