By Amy Norton
New York - Though breastfeeding is sometimes seen as a way to protect against early cavities, a new study using rats suggests that breast milk may cause more cavities than cow's milk does.
However, researchers stress, breast milk appears no more likely to contribute to cavities than commonly used infant formulas - and the animal findings should not be seen as a strike against breastfeeding.
Cavities can form when certain decay-causing bacteria in the mouth turn sugar into acids that damage the protective enamel on the teeth.
Not surprisingly, the study found that sweet liquids like soda and honey or sugar-sweetened water promoted dental erosion and cavities in baby rats.
But while animals fed human milk showed far less tooth decay than those given such sugary drinks, they did develop more cavities than rats fed cow's milk.
"Breast milk has been presumed to be protective against cavities," said study co-author Dr Ruth A Lawrence of the University of Rochester in New York.
But the current findings suggest this is not the case, she said, and they point to a potential problem in allowing older babies to breastfeed throughout the night.
Lawrence and colleague Dr William H Bowen report their findings in the October issue of the journal Pediatrics.
In general, experts recommend that babies be fed only breast milk for about the first six months of life, and that breastfeeding continue after the introduction of solid foods, until at least the age of 12 months.
Breastfeeding throughout the night before the age of six months - when babies need to feed more frequently, and have not yet developed their first teeth - is not a problem, according to Lawrence.
But allowing older babies to feed throughout the night might be, she said, particularly if a child is at greater risk of cavities because of a high prevalence of the problem in the family.
Parents are already advised not to put babies and toddlers to bed with a bottle, in order to protect their teeth from prolonged contact with the sugars in formula or any other liquids.
In addition, Lawrence and Bowen write, when a nipple - of the human or bottle variety - stays in a child's mouth for a long period, it may obstruct the flow of saliva, which is a natural cavity fighter.
It's not certain why breast milk was more cavity-promoting in this study than cow's milk was, but the researchers offer some possible explanations.
Human milk, they note, contains more lactose, a milk sugar, than the cow variety does, and the mineral content of cow's milk - which has more calcium and phosphorus - may be less likely to demineralise tooth enamel.
However, Lawrence pointed out, babies should not be given cow's milk before the age of one year. Moreover, based on past research on infant formulas, breast milk appears no more likely to promote cavities than commonly used formulas are, she said.
"There are many health benefits for promoting breastfeeding in infants," Bowen and Lawrence conclude in the report.
"Switching from breastfeeding to cow milk," they add, "is not being advocated here."