The finding mirrors a growing body of evidence suggesting that breastfeeding is beneficial for visual development; Dr. Atul Singhal of the Institute of Child Health was cited as telling Reuters.

According to Dr. Singhal and colleagues, a proposal has already been made to explain the benefit, which attributes this vision enhancing effect to a higher concentration of DHA or docosahexaenoic acid in breast milk than in formula.

DHA is an omega-3 fatty acid and some infant formula might have been fortified with it to make it more attractive to consumers.

In this study published in the January 2007 issue of American Journal of Clinical Nutrition, Dr. Singhal and team followed from birth 78 previously breast fed and 184 previously formula-fed children age 4 to 6 years.

During the first six months after birth, the formula-fed children were randomly assigned formula either with DHA or without DHA added.

The researchers found that breast fed children were significantly more likely to have better stereo-acuity than formula-fed children.   Among the formula-fed children, addition of DHA into the formula did not make any difference in stereo-acuity measurements.

Although DHA has been proposed to be the benefiting agent in breast milk, the fact that fortification of formula with DHA did not make any difference in stereo-acuity suggests that the added DHA may not work or there is something else in milk that enhances the vision.

The mechanism by which the benefit of milk can be explained remains unknown.   The early proposal that DHA may be responsible does not make sense based on what's observed in the current study.

But the researchers conclude that "these findings support the hypothesis that breast-feeding benefits long-term stereoscopic development."

Breastfeeding has been known for a battery of benefits to the infant and the mother as well.   American pedestrians recommend that infants should be breastfed for one year, if so desired by either the mother or the infant, breastfeeding can continue after one year.