Babies who are breast-fed until the age of six months are better behaved as children, researchers have found.
Experts monitored the behaviour of 1,500 children aged between seven and 11.
They found those who had only been breastfed for the first month of their life, or less, were twice as likely to display behavioural problems than those who were breastfed until six months.
The research, led by Glasgow University experts and carried out among children in South Africa, suggests breastfeeding has benefits that extend beyond physical health.
Experts have long advised that babies are fed with breast milk for at least six months, where possible, with proven benefits including a stronger immune system, improved digestive system, and lower risk of certain forms of cancer.
But experts are beginning to realise that breastfeeding also has benefits for IQ, cognitive skills, and behaviour.
The NHS suggests women should feed their babies exclusively with breast milk until they are at least six months old, and then continue breastfeeding while gradually introducing other food.
Women are advised by the NHS: ‘The longer you breastfeed, the longer the protection lasts and the greater the benefits.’
But most mothers in the UK abandon breast milk very early in their child’s life, turning instead to formula.
Only 34 per cent of British children are breastfed until six months, compared to 49 per cent in the US, 50 per cent in Germany and 62 per cent in Switzerland.
Researcher Dr Tamsen Rochat, of the Human Science Research Council in South Africa, whose work is published in the journal PLOS Medicine, said: ‘The duration of exclusive breastfeeding of an infant has greater importance than previously realised in several areas of development.
‘For example, childhood onset conduct disorders can lead to aggressive or disruptive behaviours, which interfere with learning and peer relationships, in turn leading to low self-esteem and further behavioural problems.
‘Conduct disorders that start in childhood and persist into the teen years are associated with an increase in antisocial (and potentially violent or criminal) behaviours, poor long-term mental health and low academic achievement in later life.’
It is estimated that the annual cost of crime related to people who had conduct disorders in childhood was £79 billion.
Dr Ruth Bland, of Glasgow University, added: ‘Evidence from studies in high-income countries suggests that the economic cost of conduct disorders is enormous.’
She cited previous research which suggests that the crime caused by people who had conduct disorders as children costs £60billion a year globally.
Dr Peter Singer, chief executive of Grand Challenges Canada which funded the study, said: ‘This study shows how who parents can help develop smart, social kids who make good decisions: breastfeed babies.’
The World Health Organisation warned in January that rates of breastfeeding in Britain are the lowest in the world.
Only one in every 200 children in the UK – just 0.5 per cent – are breastfed until the age of 12 months.
In comparison, 27 per cent of children in the US, 35 per cent in Norway, 44 per cent in New Zealand and 92 per cent in India are breastfed until they are one.
Unicef warns that child obesity, diabetes and infections could all be significantly reduced if more mothers could be persuaded to breastfeed.
Women themselves would also benefit, with breast cancer rates reduced among mothers who had breastfed their children.