What is depression?

Depressed man with counsellor People with depression feel persistently sad for weeks or months

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The low mood of depression is deeper, longer and more unpleasant than the short periods of unhappiness we all have from time to time. It can cause a loss of interest or pleasure in activities, and may interfere with everyday life.

What causes depression?

We are still not sure what causes depression but a combination of factors are thought to play a role. Major life events such as bereavement, redundancy or marital breakdown are all common triggers for depression.

Unhelpful thinking patterns such as imagining the worst - also known as over-generalising or 'catastrophising' ("I fail at everything") - can also contribute to a downward spiral into depression.

Some medical conditions, such as an underactive thyroid (hypothyroidism), can also cause depression. Depression is also a rare side-effect of certain drugs such as beta blockers, which are used to lower blood pressure, and some anti-epileptic drugs.

You can also develop the condition for no single obvious reason. It can come on gradually and you can end up exhausting yourself by trying to struggle on and keep busy rather than seeking help.

The role that brain chemicals play in depression is still poorly understood. However, most experts agree that it is not simply caused by an imbalance in the brain.

Who can get depression?

The short answer is: anyone can develop depression.

However, research suggests there may be a genetic factor involved that makes some more prone to the condition when going through a challenging period. People with a family history of depression are also more likely to experience it themselves. And certain genetic variations on chromosome 3 could play a role in severe and recurring depression - a disorder that affects up to 4% of the population.

The role of anti-depressants

Anti-depressants affect the way that chemicals in the brain work. But the exact role of these chemicals in depression is not fully understood, and anti-depressants do not work for everyone.

It is known that depression changes the balance of various neurotransmitters in the brain. These are the chemical messengers that communicate between brain cells called neurones.

Neurotransmitters send information across tiny spaces called synapses, which are received by a receptor embedded in the next neurone in the chain. The receptors may be oversensitive or insensitive to a specific neurotransmitter, causing their response to its release to be excessive or inadequate.

WHO IS AFFECTED?

  • About two in three adults have depression at some time in their life
  • One in four women and 1 in 10 men will require treatment for it at some point
  • The average length of an episode of depression is six to eight months
  • 4% of children suffer from anxiety or depression

Source: Patient.co.uk

Anti-depressants gradually increase the levels of 'mood-enhancing' neurotransmitters like serotonin, norepinephrine and dopamine in the brain. This may be why most people need to take the pills for a few weeks before they start to work.

However, according to the Royal College of Psychiatrists some of the benefit is due to the placebo effect. They found that 50 to 65% of people living with depression get better if given an anti-depressant compared to 25 to 30% of those given a 'dummy' pill.

First developed in the 1950s, there are now four main classes of anti-depressants and they affect these brain chemicals in slightly different ways.

The most commonly prescribed are SSRIs, or selective serotonin reuptake inhibitors, which raise the serotonin level in the brain. Serotonin and noradrenaline re-uptake inhibitors (SNRIs) are newer and also affect levels of norepinephrine.

Tricyclic antidepressants and monoamine-oxidase inhibitors (MAOIs) are older and less commonly used as they tend to cause more side-effects.

While anti-depressants can ease the immediate symptoms they do not tackle any root cause, and so are often used in combination with other therapies.

Other major types of depression

TYPE OF DEPRESSION

CAUSES

RISKS

Post-natal depression

A type of depression some women experience in the first few months after they have had a baby.

Can be a combination of factors including stress of life-changing event, difficult delivery, lack of support at home and illness following birth. Hormone changes may play a part.

Affects one in seven women after childbirth. A family history of depression or postnatal depression increases the risk as does having a mood disorder in the past.

Bipolar disorder

Moods swing from one extreme to another. Manic and depressive periods can last for weeks and may interfere with every day life.

Widely believed to be the result of chemical imbalances in the brain. Stressful life events can trigger episodes.

One in 100 people are bipolar in the UK. The disorder seems to run in families but no single gene is thought to be responsible.

Seasonal Affective Disorder

A type of depression that has a seasonal pattern. Episodes tend to occur during the shorter days of winter when the Sun's rays are weaker.

A lack of sunlight causes us to produce more of the hormone melatonin and less of the neurotransmitter Serotonin. These factors are thought to play some part in triggering SAD.

One in 50 people affected by SAD in the UK. One in seven people with a first degree relative with SAD will have the condition. It is more common in countries further from the equator.

For information on symptoms and treatment, visit NHS Choices

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