There’s no evidence that nighttime nursing itself causes cavities.1 Dr. Brian Palmer studied children’s skulls that were thousands of years old—way older than toothpaste or sealants—and he found almost no cavities.2 Makes sense. Nearly all mammals nurse at night. Most of them have teeth right from birth and never get cavities. Night-weaning your baby is almost certainly not necessary and can lead to early weaning, with everything that means to your and your baby’s health and relationship.
How your baby gets your milk matters, though. Breastfeeding doesn’t allow milk to pool around the teeth; the milk is pulled right to the back of the throat and swallowed. Expressed milk given by bottle can pool around the teeth and expose them to milk sugars for longer than normal.
The type of milk matters. Formula lacks the lactoferrin, sIgA (secretory immunoglobulin A), IgG (immunoglobulin G), and the high pH level of human milk that help inhibit cavity formation.3 It has only 1/100th the cavity-inhibiting lysozyme of human milk!4 And unlike your milk, it doesn’t deposit tooth-strengthening calcium and phosphorus.5
Anatomy matters. If your child has a tight, thick attachment of the skin that stretches between his upper lip and gum (the kind that can cause a space between the front teeth later on), it may cause milk to get trapped and grow bacteria.6
The main problem is our modern diet, not our milk.7 The prehistoric children whose teeth Palmer examined had a diet that was low in sugar. Today’s dried fruits and candy can trap sugar against tiny teeth. And processed foods like crackers and cereals may not start out as sugar, but adding saliva changes some of their starches to sugar.
There can be other reasons for modern cavities, even in children whose diets include no problem foods. Smoking and diet during pregnancy, and certain illnesses in pregnancy can make a baby’s first teeth more prone to cavities.8 (In those rare cases, their permanent teeth are almost always fine.) Streptococcus mutans, a particularly nasty mouth bacterium that some parents and children have, interacts with sugars and is especially hard on tooth enamel. Babies can pick up this bacterium from adult carriers who share food, utensils, or mouth kisses with them.
The best way to avoid cavities is to wipe or brush your child’s teeth thoroughly at least twice a day and limit sugars and sticky foods. Swishing or sipping water after eating also helps. It makes sense not to offer anything other than water or your milk after bedtime teeth cleaning. And ask your dentist about using xylitol to help fight harmful mouth bacteria.
In extreme cases, some dentists recommend wiping a child’s teeth after each nursing, including during the night (which, as you can imagine, neither mother nor baby enjoys). We haven’t found any studies, but some mothers who have done it think it made a difference.
Bottom line: Under normal circumstances, night nursing does not cause cavities unless another type of carbohydrate is present. Good oral hygiene can reduce the mouth bacteria that can cause cavities.
All citations reference La Leche League International’s new book, Sweet Sleep.