Sugar and tooth decay — what the research (and the WHO) actually say
It's not the amount of sugar that's worst for your teeth — it's how often you consume it. Here's what the WHO, Sweden's Food Agency, and dental research say about the sweetest threat to your oral health.
Sugar and tooth decay — what the research (and the WHO) actually say
We know sugar is bad for teeth. But exactly how bad, and what matters most — the amount, the frequency, the type? The answer is actually pretty clear in the research, and it could change how you eat.
How sugar damages teeth
When you eat or drink something containing sugar, mouth bacteria — especially Streptococcus mutans — convert the sugar into acid. The acid lowers the pH in your mouth, and when pH drops below about 5.5, the enamel on your teeth begins to dissolve. This is the Stephan curve, named after dentist Robert Stephan who mapped the process in the 1940s.
As long as pH stays low, mineral loss continues. Your saliva then starts to neutralise the acid and restore pH — a process that takes about 30–60 minutes. During that time, the tooth is vulnerable.
Frequency matters more than amount
This is the key insight: if you drink a whole bottle of soda in five minutes, you get one acid attack. If you sip the same amount over an hour, you get a continuous acid attack. The second version is much worse for your teeth.
That's why the classic recommendation is: eat sweet things with meals, not between them. Sweden's Food Agency emphasises the same principle in its nutrition advice.1
What the WHO says about sugar intake
The WHO's official recommendation, published in 2015 and updated since:2
- Free sugars should make up less than 10 % of total energy intake
- A further reduction to below 5 % brings additional health gains — especially for teeth
5 % of energy intake works out to about 25 grams of sugar a day for an adult — less than a standard soda can (33 cl = ~35 grams of sugar).
Free sugars — what are they?
The term "free sugars" is central. It means:
- Sugar added to food and drink (sodas, candy, baked goods, sauces)
- Naturally occurring sugar in fruit juice, honey, and syrup
It does not include:
- Sugar in whole fruit (the fibre and structure slow absorption)
- Lactose in milk and dairy
This distinction matters — eating an orange is not the same as drinking orange juice, even if the total sugar is similar.
Concrete tips from the research
- Limit the number of "sugar moments" to four a day. Breakfast, lunch, dinner, and one snack — not constant grazing.
- Eat sweets with meals — saliva flow is already high and neutralises acid faster.
- Drink water afterwards — it rinses acid and sugar off tooth surfaces.
- Don't brush right after something sweet. Wait 30 minutes so the enamel can remineralise. Brushing softened enamel wears it down.
- Xylitol gum after meals stimulates saliva and can help normalise pH faster — especially useful when brushing isn't possible.
Summary
- Sugar causes cavities because bacteria convert it into acid that dissolves enamel
- Frequency matters more than amount — grazing is worse than a big portion
- The WHO recommends under 10 % free sugars of total energy intake, ideally under 5 %
- Eat sweets with meals, drink water after, don't brush immediately