The majority of people who kill themselves in that age group do so because they are depressed.

But Swedish researchers, writing in the British Medical Journal, suggest there may be a stronger link between serious illness and suicide than previously thought.

They found physical illness was associated with a four-fold increase in suicide rate.

Mental illness in old age can be treated and some suicides prevented with recognition, the newer medications, and counselling

Marjorie Wallace, SANE

Suffering from sight problems, neurological disorders and potentially fatal diseases were all specifically linked to an increased suicide risk.

The study looked at records for 46 men and 39 women, aged 65 years and over, who had committed suicide.

These were compared with 84 men and 69 women of the same age, living in the same area.

The researchers also interviewed relatives of both groups.

Age discrimination

Although the connection between physical illness and suicide risk has been studied before, this is the first time it has been quantified, the researchers said.

Men with serious illness appeared to more likely than women who were as ill to commit suicide.

Mental illness was strongly linked with suicide.

The research team from Gothenburg University, led by Margda Waern, admitted the study had been small and might not be reflected in other countries where suicide rates were higher or lower than Sweden's.

Dr Waern told BBC News Online doctors were taking more notice of the mental health of elderly patients with physical illnesses.

She said: "Things are improving, but there's still a very long way to go.

"In my daily life as a psychiatrist, I meet people who say 'of course this patient is depressed, he has a serious illness, he has reason to have a psychiatric reaction'.

"This is ageist. If you had a young person in a car accident, and they developed a depression after that, you would treat the depression.

"But when an older person with a serious illness becomes depressed, it's seen as 'natural'.

"However, both illnesses need to be addressed."

'Don't overlook depression'

Marjorie Wallace, chief executive of the mental health charity SANE, said: "Mental illness in old age can be treated and some suicides prevented with recognition, the newer medications, and counselling.

"We have been concentrating so much on young people that we tend to forget older people, whose depression is often overlooked and considered inevitable although there is considerable evidence that the new anti-depressants can transform their outlook on life.

"It is also vital that warnings, from both individuals and their families, are taken seriously.

"In a study of over 10,000 people who contacted our helpline mentioning a history of mental illness and suicidal intentions, 83% had consulted a doctor or other professional within the previous four weeks."