NEW YORK (CNN) — New research suggests that the longer a child is breast-fed, the bigger the risk of developing cavities in their teeth.

The study published in the journal “Pediatrics” looked at more than 1,000 children in one Brazilian city. At age five, all of them were examined for cavities by dentists.

Researchers found that children who were breast-fed two years or longer had more than twice the risk of having severe cavities compared to kids breast-fed for less than a year.

“Severe” is defined for this study as having at least six cavities.

Researchers suggest the uptick is due to the older children likely being breast-fed on demand, making it harder to clean their teeth.

Experts say it’s vital that babies have their gums wiped down after breast-feeding, as breast milk contains sugar. In addition, children should start going to the dentist as soon as their first tooth comes in.