A woman breastfeeds her daughter at a restaurant in 2008. (Mark Blinch/Reuters)

Prolonged, exclusive breastfeeding appears to give children a cognitive advantage over formula-fed kids, increasing IQ by three to four points on average and boosting later academic performance, a Canadian study suggests.

The research by McGill University is not the first to link the method of infant feeding to brain development, but the size and design of the study lends weight to the idea that breastfeeding actually causes an increase in intelligence.

"Our study provides the strongest evidence to date that prolonged and exclusive breastfeeding makes kids smarter," said lead investigator Dr. Michael Kramer, a professor of pediatrics and epidemiology at McGill.

Kramer and his team evaluated about 14,000 children in 31 hospitals and clinics in Belarus starting in 1996, following their progress until they were 6 1/2 years old. Half the mothers were exposed to an intervention that encouraged prolonged and exclusive breastfeeding (experimental group), while the other half continued usual maternity hospital and out-patient pediatric care (control group).

Mothers who visited a facility promoting breastfeeding in the former Soviet country were more likely to feed their infants only breast milk at age three months (43.3 per cent versus 6.4 per cent in the control group) and at all ages through 12 months.

By the time children reached an average age of 6½, those in the breastfeeding group scored higher on tests measuring verbal intelligence, non-verbal intelligence and overall intelligence.

An achievable goal for most mothers: professor

Breastfed children also performed significantly higher academically than formula-fed children, found the study, published in the May issue of Archives of General Psychiatry.

The children's cognitive ability was assessed by IQ tests administered by their pediatricians and by their teachers' ratings of their performance in reading, writing, mathematics and other subjects.

"I think that what this says is your average mother in a developed country like Canada who succeeds in breastfeeding for the duration and the degree of exclusivity achieved by the women in our experimental group … can expect her child to be a few points higher in IQ."

The average jump in IQ is not so crucial when it comes to the individual child, Kramer said. "But if you consider for the whole population shifting the mean (IQ score) up three or four points, that means fewer difficulties for kids at the lower end and more Einsteins and Mozarts at the high end."

Still, Kramer stressed that women who are unable to breastfeed or choose not to for a variety of reasons should not feel guilty or worry their child will be less intelligent as a result of being formula-fed.

"I think this [prolonged, exclusive breastfeeding] is a goal that's achievable by the vast majority of mothers," he said.

"Those who cannot — and there are some who cannot — and there are some who could but don't want to, have other ways of stimulating their children and improving their IQ, like reading and playing with their children.

"And it might even be that the effect that we're seeing is not something in the [breast] milk but has something to do with the nature of the contact, the physical contact or with what transpires between the mother and the baby verbally or emotionally at the time of the feeding, and that maybe is transposable to other feeding modes."

Other factors could cause higher IQ

Putting the study's findings into context for parents, Kramer said "the difference of three or four IQ points is not going to make a difference between a child finishing school or being a success or a failure.

"This is not the difference between mental retardation and a genius."

Commenting on the study, Dr. Jack Newman said that while the research does not prove without a doubt that breastfeeding raises intelligence levels in children, there are sound reasons for believing it could.

For one, breast milk contains naturally occurring omega 3 and 6 fatty acids and a compound known as IGF-1, all of which have been linked to increased cognitive ability.

"It may be the breast milk itself, although it could be all the things that are associated with it," he said, referring to the physical and emotional contact inherent in breastfeeding.

The co-founder of the Newman Breastfeeding Clinic and Institute in Toronto also said many women who are unable to breastfeed feel terrible guilt, but he believes too often they have been failed by the medical system.

"Whether every mother can successfully breastfeed is an issue, but in fact most of the mothers who have difficulty with breastfeeding shouldn't have problems with breastfeeding," he said.

"Most mothers produce plenty of milk and if they got the help and the advice that they should be getting they would not 'fail.' "

The Canadian Paediatric Society recommends exclusive breastfeeding for the first six months, although a mother can continue to breastfeed along with giving solid foods until the child is two years or more.