Infants exclusively breastfed for the first three months of life or longer score nearly six points higher on IQ tests at the age of 6 than infants who weren't breastfed exclusively, a new study reports.

The findings further strengthen previous research works that concluded that children who were breast-fed as infants scored better on IQ tests and other measures of cognitive development milestones.

Though, why breast-feeding increases cognitive skills among children isn't clear, the researchers note that “It could be something in the milk or it could be the physical contact between the mother and the baby."

The findings are published in the May issue of the Archives of General Psychiatry.

For the study, the researchers took up nearly 14, 000 infants. Around 7,000 infants were randomly assigned to exclusive breastfeeding, while another 6,781 infants received the usual practice of breastfeeding plus other foods.

When the children were 6.5 years old they were given a standard IQ test. Those children who were exclusively breastfed scored, on average, 7.5 points higher in verbal intelligence, 2.9 points higher in nonverbal intelligence, and 5.9 points higher in overall intelligence, the researchers noted.

In addition, the breastfed children had significantly better academic performance in both reading and writing, compared with children who weren't breast-fed exclusively.

Certain amino acids including omega three fatty acids and DHA (Docosahexaenoic acid) and cholesterol found in mothers' milk are not found in formula feeds. These are believed to be better for infants' developing brains.

Pediatricians and health experts recommend exclusive breastfeeding for the first six months on infants’ life as the best way to improve infants' overall health and build their immune system.

According to the U.S. Food and Drug Administration, breast-fed infants have fewer hospital admissions, ear infections, diarrhea, rashes, allergies and other medical problems than bottle-fed babies.