Children born to men in their mid to late 30s are more likely to develop the disease than those born to men in their early 30s, according to a study reported in The New Scientist.

Alzheimer's is a degenerative disease of the brain which destroys memory and eventually all other mental functions.

Previous research has shown that older mothers are more likely to give birth to babies with Down's syndrome and that people with Down's are likely to develop Alzheimer's.

They also tend to show signs of the disease at an earlier age.

Parental age

Researchers at the Technical University of Munich were intrigued by the association and investigated the link between a parent's age and the child's risk of developing Alzheimer's.

Led by Dr Lars Bertram, the team studied 206 patients with Alzheimer's disease.

Alzheimer's worsens with age

The researchers studied the incidence of the disease in each of the subjects' families to establish how likely it was that the sufferers' genes were responsible for the condition.

They then split the subjects into two groups: high risk and low risk. People who had several relatives with Alzheimer's were deemed to have a higher genetic risk of developing the disease.

Their fathers tended to be aged between 31 and 33 when they were born.

However, the fathers of those in the low genetic risk group tended to be between 35- and 37-years-old when their child was born.

DNA damage

The scientists suspect that the ageing process damages DNA.

People having children later in life are therefore more likely to pass on flawed genes.

Dr Bertram said: "There is an accumulation of environmental factors which somehow alter the genome (genetic make-up) of the father."

The Alzheimer's Disease Society welcomed the research, but was cautious about its significance when taken on its own.