People with higher IQs are more likely to live into healthy old age, according to a study.

Unfortunately, those who do not perform so well in intelligence tests could suffer a higher risk of heart disease, fatal accidents and suicide.

The discovery was made after researchers looked into the medical records of one million Swedish army conscripts.

After taking into account whether they had grown up in a safer, more affluent environment, they established the connection between IQ and mortality.

One of the researchers, Dr David Batty, said the statistics showed "a strong link between cognitive ability and the risk of death."

He added: "People with higher IQ test scores tend to be less likely to smoke or drink alcohol heavily. They also eat better diets, and they are more physically active. So they have a range of better behaviours that may partly explain their lower mortality risk."

Previous studies have suggested that pre-school education programmes and improved nourishment can raise IQ scores. They may also have "previously unforeseen health benefits, further validating government efforts to improve living conditions and education", the researchers believed.

Dr Batty, a Wellcome Trust research fellow at the Medical Research Council's Social and Public Health Sciences Unit in Glasgow, said: "If you believe the association between IQ and mortality is at least partially explained by people with a lower IQ having worse behaviours - which is plausible - then it might be that the messages used to change health behaviours are too complicated."

A second study, also co-authored by Dr Batty, used data from more than 4,000 US soldiers and followed them for 15 years. The study found the same relationship between IQ scores and mortality.