The findings are based on data from the ground-breaking Raine Study at the Telethon Institute for Child Health Research, that has tracked the growth and development of more than 2500 West Australian children over the past 16 years.

Researcher Dr Wendy Oddy said there was growing evidence that bioactive factors in breast milk played an important role in the rapid early brain development that occurs in the first year of life.

"Even when we adjust the results to take into account other factors such as the parents' socio-economic situation, their education, their happiness and family functioning, we see that children that were breastfed for at least six months are at lower risk of mental health problems," Dr Oddy said.

The study found that children who were breastfed for less than six months compared to six months or longer had a 52% increased risk of a mental health problem at 2 years of age, a 55% increased risk at age 6, at age 8 the increased risk was 61% while at age 10 the increased risk was 37%.

The analysis is based on a scientifically recognised checklist of child behaviour that assessed the study children's behaviour at 2, 6, 8 and 10 years of age.

Dr Oddy said that children that were breastfed had particularly lower rates of delinquent, aggressive and anti-social behaviour, and overall were less depressed, anxious or withdrawn.

"These results are powerful evidence for more support to be given to mothers to help them breastfeed for longer," she said.