Hi Silia
I would have to look at this paper in its entirety to be sure but I don't think it 'disproves' - or proves - anything.  Cohort studies, however well designed, don't prove or disprove anything. They do provide evidence - a piece of the puzzle - but one study does not constitute an body of evidence and it certainly doesn't offer a proof.
The evidence around the influence of artificial feeding on cognitive development is complex and some would say contradictory.  What it is important to notice about this study is that it compares children for whom breast milk or DHA-fortified formula was the main method of feeding throughout the first 6 months with those fed unfortified infant formula.  It does not appear to compare children who were exclusively breastfed from birth with those who were fed infant formula, fortified or otherwise.  
It concludes that DHA intake does not appear to influence neuropsychological function in preschoolers ... and appears to make no distinction between children fed commercially derived DHA and those fed breastmilk ... it also appears to fail to take account of maternal DHA intake, which is known to alter the fat profile of her milk.
It further concludes that 'advantages' in cognitive development previously attributed to breastfeeding may to due to confounding by maternal and family characteristics.  It does not appear to entertain the notion that breastfeeding is more than the milk ... and that the hormonal changes in the mother that make her more responsive to the baby and less responsive to stressful stimuli, the increased proximity required by breastfeeding, the increased interaction between mother and baby necessitated by breastfeeding might account for the differences in cognitive development between breastfed and formula fed babies.  None of these things would be confounders because they are integral to breastfeeding.
Regards
Nina Berry
Centre for Health Initiatives
University of Wollongong
Australia

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