BY DHANY OSMAN

Depression is caused by imbalances in the neurotransmitter levels within the brain.

Neurotransmitters are the brain chemicals that help to regulate a person's mood and emotional state.

Major depressive disorder, or clinical depression, can come in many sub-types.

Generally, women are almost twice as likely to suffer from depression than men.

Those who are suffering from multiple medical conditions - like diabetes or hypertension - are also more susceptible, like the elderly who are facing deteriorating health.

With the exception of a few cases, most types can be treated with a combination of counselling and antidepressant medication.

These are some forms of depression:

Dysthymia

What it is: Dysthymia is a low-grade depression in which a person feels depressive symptoms - like insomnia, loss of appetite and tiredness - over a long period of time, usually two years or more.

Its milder symptoms still allow a person to function, albeit less efficiently.

Psychiatrist Adrian Wang said that dysthymia sufferers appear chronically unhappy, although many may dismiss such feelings as character flaws.

Left unchecked, dysthymia can lead to severe depression, or major depressive bouts, over time.

Treatment: Psychotherapy is the preferred form of treatment.

Counselling can first be used to address feelings of hopelessness. Cognitive and behavioural therapy can then be undertaken to help patients identify, prioritise and deal with their life problems.

Given the chronic nature of dysthymia, antidepressant medication is often recommended too.

Seasonal Affective Disorder (SAD)

What it is: SAD is usually seen in temperate climates where patients experience symptoms of depression during the dark winter months.

Short days and long nights, experts suggest, can affect melatonin (a hormone) and seratonin (a neurotransmitter) levels in the brain, thus creating the biological conditions for depression.

Treatment: Beyond antidepressants and counselling, some patients have been reported to respond positively to light-exposure therapy which involves the use of light boxes to simulate dawn or day-time light conditions.

Post-partum depression

What it is: Also known as post-natal depression, it can occur in new mothers within a year of childbirth.

This is due to the combination of hormonal, physical and psychological changes undergone following delivery.

In severe cases, post-natal depression can lead to suicide or even infanticide.

Early last year, British newspapers reported how postnatal depression drove Mrs Susan Talby, 41, to murder her two sons and then hang herself.

Treatment: Psychological therapy is crucial in the treatment of depressed women as they are more in tune with their emotions and need to express them, said Dr Helen Chen, head of mental wellness service at KK Women's and Children's Hospital.

Family and marriage counselling may also be advised as it can often affect spouses and children as well.

She said that in prescribing medication, special consideration needs to be taken so as not to impact a woman's reproductive system.

Adjustment disorder with depressed mood

What it is: Often called 'reactive depression', it is characterised as depressive symptoms which arise from a specific stressor, usually a life-event like divorce, job stress or even the current economic crisis.

While symptoms may be milder compared to other forms of depression, they can still impair a person's ability to function normally.

In Singapore, Dr Wang said that it is commonly seen in young men starting on National Service and those feeling the stress of a new job.

Treatment: In counselling those with adjustment disorder, specific emphasis is usually placed on identifying and dealing with the source of the distress.

This can involve making lifestyle changes - switching jobs if work stress is the source, for instance - or finding creative solutions to deal with a problem.

Bipolar disorder

What it is: Also known as manic depression, patients can experience extreme fluctuations between abnormally elevated moods (mania) and severe depressive episodes, which can put one at risk of suicide.

Extreme manic depressives can also experience delusions and hallucinations.

Considered to be a chronic condition, it can arise in adolesence and continue through adulthood.

Research has suggested a strong genetic influence in bipolar disorder, with each sufferer going through their own unique cycle of manic depressive bouts.

Clyclothymia, on the other hand, is a milder form of bipolar disorder in which patients experience less extreme mood swings.

Treatment: Dr Wang said that bipolar treatment is generally very reliant on medication.

In such cases, mood stabilisers are used instead of antidepressants, as the latter can worsen a patient's condition.

Mood stabilisers not only help to alleviate a patient's depressive mood but also keep it from fluctuating, he said.

This article was first published in Mind Your Body, The Straits Times on Dec 11, 2008.