Babies who are breastfed are less likely to have behavioural problems by the age of five than those given formula milk, according to new research. The question of whether breastfeeding has a long-term impact on behaviour has been investigated before, but the studies have usually been small-scale and inconsistent in their findings. But a large research project carried out by the universities of Oxford, Essex and York, together with University College London, has come to a more robust conclusion. They used data from the ongoing Millennium Cohort Study, a survey of babies born in the UK during a 12-month period between 2000 and 2001. More than 10,000 mother and baby pairs of white ethnic background took part. They were interviewed when the baby was nine months old and again at two-yearly intervals. The researchers asked parents to fill in questionnaires to assess their children 's potential behavioural difficulties. These included emotional issues such as c...