A brilliant scientist friend of mine found himself totally depressed. In fact his depression was so intense he couldn't leave his house. He would sit by himself all day in a room and not speak a word. Yet when I was able to talk to him, his amazing mind was still active and capable of handling all the intellectual rigor of his research.

However there was a sadness, a forlornness which had invaded his life which he just couldn't get rid of, despite his every attempt. It was totally debilitating.

I can remember thinking at the time how odd it was to have all that ability and yet not have the capacity to deal with the depression. How could such a great mind have no control over itself?

After many difficult conversations with my friend, I became much more aware of the battle he was facing. Not only was he dealing with an illness which he didn't want, he was deeply concerned about the impact it was having on his family and his work. And to add to his burden, he had to deal with the stigma associated with depression.

Depression is generally understood as lowness and anxiety, which we can all face from time to time. Up to 1 in 10 people however will suffer from deep depression and twice as many women. It is that common.

Severe depression is more than deep sadness or melancholy. It is an invasive overwhelming condition which affects every level of our life. But what causes it?

Do traumatic events early in our lives, such as loss of a parent, create a depressive state? Is it how we have been parented? Is it triggered by crisis events in our adult life or is it brought about by a chemical imbalance in our brains? It seems all these things can contribute.

One thing is clear. Its incidence is increasing, particularly among the younger population.

The mean age for depression is now less than 30 years. So has it something to do with changes in our society, our belief systems or even our diet? Is it due to family breakdown or greater expectations and pressures? Maybe modern life with all its new technology still leaves us feeling unsatisfied, unfulfilled and unsupported.

Unexpected crisis in our lives can certainly trigger depression. A death, a relationship breakdown, a job loss, a failure - all can bring about depression. But not for every one. For some people, major life crises have profound and disturbing results.

Does this mean that some of us are more genetically or psychologically predisposed to depressive states?

As you can see there are no ready made answers. However a great deal of research has been done on depression and current forms of treatment are certainly helping many people.

But how do we overcome the stigma associated depression and mental illnesses?

My scientist friend sometimes found the stigma almost unbearable. He felt at times 'written off' as lazy, weak, self-centered or mad. Some people suggested he should "snap out of it" or "pull up his socks". Other people didn't want to know him any more or became angry because he didn't want to socialize. While many were very supportive others were totally dismissive.

It is so easy to become judgmental and stigmatize people who suffer from depression and other mental illnesses.

Such attitudes say more about our society and ourselves than about the people suffering from these conditions.