If people want to reduce their risk of tooth decay, the amount of ‘free sugars' they eat should make up less than 10% of their total calorie intake, researchers have said.

Free sugars are sugars that are added to foods by the cook, consumer or manufacturer. They are also the sugars naturally present in fruit juices, fruit concentrates, honey and syrups.

Since 1990, the World Health Organisation (WHO) has recommended that the consumption of free sugars should not exceed 10% of daily calorie intake. It recently commissioned UK researchers to review these guidelines.

The team from Newcastle University found that this 10% threshold is beneficial, as people who stay under it have much lower levels of tooth decay. The team also found that lowering the threshold to 5% - around five teaspoons of sugar per day - protects teeth even more.

"People now expect to keep their teeth into old age and given that the effects of sugars on our teeth are lifelong, then limiting sugars to less than 5% of the calories we eat would minimise the risk of dental caries (cavities) throughout life," explained Prof Paula Moynihan of Newcastle University.

She noted that while sugary foods used to be an occasional treat, they are ‘now staples in many people's diets'.

"In the past, judgements on recommended levels of free sugars intake were made based on levels associated with an average of three or fewer decayed teeth in 12-year-olds. However, tooth decay is a progressive disease. By looking at patterns of tooth decay in populations over time, we now know that children with less than three cavities at age 12, go on to develop a high number of cavities in adulthood," Prof Moynihan noted.

As part of the research, 55 studies dating back as far as 1950 were analysed.

Prof Moynihan emphasised that the public needs better information on the health risks associated with sugary foods and drinks.

"We need to make it easier for people to make healthier choices when it comes to sugars by ensuring that options lower in added sugars are made widely available in schools, shops and the workplace," she added.

Details of these findings are published in the Journal of Dental Research.