Researchers from the University of California, Berkeley, studied a link between longer-term breastfeeding and cavities in 458 babies in Porto Alegre, Brazil. They found that the more frequently a mother breastfeeds her child after the age of two, the more likely the child is to have rotting teeth.
One of the reasons for this could be that breast milk contains excess sugar from modern refined foods, the scientists said.
For the study, the researchers checked in on babies when they were six, 12 and 38 months old.
At six months, the study team gathered data on the number of breast milk bottles the baby drank the day before and any other liquids, like juice.
At the 12-month mark, parents reported whether they fed their babies any of 29 specific foods, including fruits, vegetables, beans, organ meat, candy chips, chocolate milk, cookies, honey, soft drinks or sweet biscuits.
Two trained dentists examined all of the babies at each of the visits. Nearly half of the children had consumed a prepared infant formula drink by six months, but very few still drank formula by their first birthday.
The researchers, who revealed their findings in the Annals of Epidemiology, found that about 40.
Lead researcher Benjamin Chaffee told Reuters: "The No. 1 priority for the breastfeeding mother is to make sure that her child is getting optimal nutrition.
"(And) our study does not suggest that breastfeeding causes dental caries. It is possible that breast milk in conjunction with excess refined sugar in modern foods may be contributing to the greater tooth decay seen in babies breastfed the longest and most often."
The report said more research is needed to determine what's going on, but the findings are in keeping with professional dental guidelines that suggest avoiding on-demand breastfeeding after a baby's teeth come through.
William Bowen, professor emeritus in the Center for Oral Biology at the University of Rochester Medical Center in New York said it's very easy to clean an infant's teeth.
He said a simple wipe in the mouth with a water-dampened cloth or Q-tip can effectively remove food before the baby's first teeth.
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