14 Breastfeeding and decay
This is the flagship example of the argument in Chapter 3, and it is also the chapter where getting the framing wrong would do the most harm.
So let me put the conclusion at the top. Nothing in this chapter is an argument against breastfeeding. The case for breastfeeding rests on a large body of evidence about infant health that has nothing to do with teeth, and it is not in question here. What is in question is a specific caries claim attached to it, and whether a Strong label on a dental guideline is the right way to carry that claim.
The advice
Breastfed babies experience less tooth decay and breastfeeding provides the best nutrition for a baby’s overall health. Support mothers to:
- breastfeed exclusively for around the first 6 months of a baby’s life
- continue breastfeeding while introducing solids from around the age of 6 months
Strength of recommendation: Strong
— Delivering Better Oral Health, chapter 2, table 1a (1)
What the guideline says its evidence is
Recommendation based on WHO guidelines, taking into account benefits of exclusive breastfeeding for first 6 months on overall health, as well as low certainty evidence of a dental caries-preventive effect. Weaning advice is from UK SACN guidelines. Some very low certainty evidence of increase in dental caries risk beyond 12 months breastfeeding, but this was observed in children experiencing high frequency of nocturnal breastfeeding and may also be influenced by confounders that the studies did not assess, for example, sugar-sweetened food and drink consumption.
— Delivering Better Oral Health, chapter 13, table 1 (1)
Read that carefully, because it is one of the most honest paragraphs in the whole guideline. It says the Strong label comes primarily from WHO guidance on overall health. It rates the caries-preventive claim low certainty. It discloses a signal in the opposite direction beyond 12 months, rates that very low, and volunteers the confounder that might explain it.
That is a panel showing its working. My complaint is not with this paragraph. It is with the fact that a reader of the summary table sees only the sentence “Breastfed babies experience less tooth decay”, stated flatly, with Strong beside it.
What the evidence actually shows
The citation is Tham and colleagues’ systematic review and meta-analysis, which included 63 papers (2).
| Comparison | Odds ratio | 95% CI | I² |
|---|---|---|---|
| More vs less breastfeeding, up to 12 months | 0.50 | 0.25 to 0.99 | 86.8% |
| Breastfed >12 months vs <12 months | 1.99 | 1.35 to 2.95 | 69.3% |
| Among those breastfed >12 months: nocturnal or more frequent feeding | 7.14 | 3.14 to 16.23 | 77.1% |
Three things jump out.
The protective estimate is fragile. OR 0.50 sounds substantial, but the confidence interval runs to 0.99. It only just excludes no effect. And I² of 86.8% is extreme heterogeneity: the studies being pooled disagree with each other profoundly. A pooled estimate with that much inconsistency is a weak summary of a scattered literature, and low certainty is the right rating.
The direction reverses after 12 months. Children breastfed beyond a year had roughly twice the odds of caries. DBOH reports this, rates it very low, and correctly notes it may be confounded.
The nocturnal figure is the one to be careful with. OR 7.14 is a large number and it will be quoted. Its interval runs from 3.14 to 16.23, which is enormously wide, I² is 77%, and it comes from five observational studies. The review’s own authors are explicit about the limitation:
There was a lack of studies on children aged >12 months simultaneously assessing caries risk in breastfed, bottle-fed and children not bottle or breastfed, alongside specific breastfeeding practices, consuming sweet drinks and foods, and oral hygiene practices limiting our ability to tease out the risks attributable to each.
— Tham and colleagues, 2015 (2)
That sentence should accompany the number every time it is used. Children who are breastfed frequently at night after their first birthday differ from other children in many ways, and the studies could not separate them.
The review’s own conclusion is deliberately modest: “Breastfeeding in infancy may protect against dental caries. Further research needed to understand the increased risk of caries in children breastfed after 12 months.”
Chapter 21 argued that a Strong recommendation with no direct evidence can be justified when a component is necessary to a well-supported pathway. Something similar, but not identical, is happening here.
The Strong label is not really being earned by the caries evidence. DBOH says so: it rests on WHO guidance about overall infant health, which is a large and separate literature that this book has not audited and is not qualified to audit. If the recommendation read “breastfeed for the reasons WHO gives; the dental evidence is weak but points the same way”, it would be unimpeachable.
Is that a legitimate borrowing? I think so, and more clearly than in the brushing bundle. The advice is correct on other grounds, following it costs nothing dentally, and the alternative, a dental guideline conspicuously declining to endorse breastfeeding, would be actively harmful and would be reported as a dental body casting doubt on infant feeding advice. There is no version of this recommendation that should be weaker.
The problem is confined to one sentence: “Breastfed babies experience less tooth decay.” Stated flatly, next to Strong, that is a stronger claim than OR 0.50 (0.25 to 0.99) with I² of 86.8% supports. “May experience less tooth decay” would cost nothing and would be true.
The part nobody says out loud
There is a real clinical issue underneath the 12-month finding, and I want to state it carefully because it is easy to weaponise.
Prolonged frequent night feeding, of anything, keeps fermentable carbohydrate against the teeth during the hours when saliva flow is lowest. That is the same mechanism as Chapter 6, and it is why the guideline elsewhere tells parents not to put babies to bed with a bottle. Whether it applies to breastmilk to the same degree as to formula or juice is genuinely disputed, and the studies that would settle it have not been done.
What a parent should take from this is not “stop breastfeeding”. It is that once teeth are present, cleaning them matters, and that is a recommendation with far better evidence behind it than anything in this chapter.
PubMed, 21 August 2026, for systematic reviews of breastfeeding and dental caries published since Tham 2015. Tham remains the review DBOH relies on. I have its full text, supplied during writing.
Limitation of this chapter. I have audited the dental claim only. The WHO guidance on exclusive breastfeeding, which is what the Strong label actually rests on, concerns infant nutrition, infection and mortality. Auditing it is outside this book’s scope and outside my competence, and I have not attempted it.
Full record in appraisals/searches/ch14-breastfeeding.md.
Verdict
- Certainty of evidence
- Low that breastfeeding up to 12 months reduces caries: one pooled estimate whose interval nearly touches no effect, with I² of 86.8%. Very low for the increased risk beyond 12 months and for the nocturnal-feeding figure. This matches DBOH’s own ratings exactly.
- Directness to the advice as worded
- Adequate on population and outcome, poor on the causal claim. These are observational studies in the right children measuring caries, and they cannot separate breastfeeding from the social and dietary factors that travel with it. The review says so.
- Is the strength label defensible?
-
Yes, for the recommendation. No, for the sentence.
The recommendation to breastfeed is correctly Strong, on grounds DBOH states plainly and which lie outside dentistry. That is legitimate borrowing, and demanding otherwise would be both wrong and harmful.
But the flat assertion “Breastfed babies experience less tooth decay”, presented in the advice column with a Strong label, outruns the low-certainty, highly heterogeneous evidence behind it. One word, “may”, would fix it.
- What would change my mind
- A cohort study following children from birth that measures breastfeeding duration and night-feeding frequency prospectively, alongside sugar intake, toothbrushing and socioeconomic position, with caries at age five. The review identifies precisely this gap. Until someone fills it, the 12-month reversal stays uninterpretable.
What this means for you
Breastfeed if you can, for the reasons your midwife and health visitor give you. Those reasons are about your baby’s overall health, they are much better established than anything in this chapter, and no dental finding should shift them.
On teeth specifically: the evidence that breastfeeding protects against decay is weak and inconsistent, and the evidence about feeding beyond a year points the other way but is weaker still and probably confounded. Neither is a reason to do anything differently.
The thing that is well established, and which applies from the moment the first tooth appears, is in Chapter 8: brush it, with fluoride toothpaste.