Babies with a very low birth weight may have an increased risk of developing psychiatric problems as adults, a new study suggests.

However, they also have a lower risk of developing alcohol or drug problems.

Babies born prematurely usually have a low birth weight. Canadian researchers set out to investigate whether having an extremely low birth weight - less than 1,000g (2lbs, 2ozs) - affected mental health later in life.

They focused on 84 adults who were born weighing less than 1,000g between 1977 and 1982. These were compared with 90 normal weight babies.

The study found that when the participants reached their 30s, those who weighed less than 1,000g at birth were almost three times less likely to develop an alcohol or drug problem.

However, they were almost 2.5 times more likely than normal weight babies to develop a psychiatric problem by their early 30s, including anxiety, depression and ADHD (attention deficit hyperactivity disorder).

Furthermore, if the mothers of these low birth weight babies received a full course of steroids before they gave birth, the babies were almost 4.5 times more likely to go on to develop psychiatric problems in adulthood and they did not appear to be protected from alcohol or drug problems.

Steroids are often given to women if they are at risk of premature labour to help the lung development of their babies.

"Importantly, we have identified psychiatric risks that may develop for extremely low birth weight survivors as they become adults, and this understanding will help us better predict, detect and treat mental disorders in this population," commented lead study author, Dr Ryan Van Lieshout, of McMaster University in Ontario.

Details of these findings are published in the journal, Pediatrics.