“Sugar intake should be halved to just five teaspoons a day,” reports The Daily Telegraph, while somewhat confusingly the Mail Online website says we should be eating less than seven teaspoons of sugar a day.
Both reports are based on a large review that looked at the link between sugar intake and tooth decay. It found that the incidence of tooth decay is lower when sugar makes up less than 10% of the total recommended calorie intake. As a very rough equivalent, that would correspond to a standard can of cola.
There was also some poor quality evidence that showed that dental decay could be further reduced if sugar made up less than 5% of calorie intake.
The references to “spoonfuls” of sugar in the papers is potentially misleading and unhelpful, as people could think this only refers to sugar added to hot drinks.
Sugar is consumed not just in the form of table sugar, but in high-sugar foods such as cakes, biscuits and fizzy drinks. It can also be found in foods you might assume are sugar-free, such as tinned chilli and ready-meal noodles, so it is always a good idea to check the label.
The current advice is to limit your added sugar intake to 10% or less of your daily calories. That’s about 70g of sugar for men and 50g for women, although this will vary according to factors such as size, age and how active people are.
Where did the story come from?
The study was carried out by researchers from Newcastle University and the University of Cambridge. It was funded by Newcastle University’s Centre for Oral Health Research and published in the peer-reviewed Journal of Dental Research.
The quality of the reporting on this study was mixed. The Telegraph reported that researchers recommend halving the current 10% threshold to 5%, when the study clearly says that evidence for doing this is “very low quality”.
The Mail made a similar mistake, although it did say later in its story that the evidence for doing this was unreliable.
Both papers also issued conflicting messages about the recommended number of teaspoons of sugar people should have a day – five teaspoons in the Telegraph and seven teaspoons in the Mail.
It is possible that this confusion arose because of a failure to realise that the recommended daily sugar intakes vary by gender. Halving the current 10% recommendation of 70g for men and 50g for women would lead to a drop (roughly) of 14 teaspoons to seven for men, and 10 teaspoons to five for women.
What kind of research was this?
This was a systematic review looking at the link between sugar intake and dental caries (cavities caused by tooth decay) undertaken on behalf of the World Health Organization (WHO). WHO sets guidelines on sugar intake as a percentage of total calorie consumption. It currently recommends that sugar intake should not be more than 10% of total calories.
The researchers say that it is widely accepted that sugar is the most important dietary factor in the development of dental caries. WHO commissioned a systematic review of evidence on this issue in 2010 to inform and update its guidelines on sugar intake.
In particular, WHO wanted to know whether increasing or decreasing sugar intake affected measures of dental caries, and whether the evidence supports a threshold for sugar intake.
Sugar comes in many different forms, including fructose, sucrose (table sugar), dextrose and glucose. It is added to lots of foods, such as sweets, chocolate, cakes and some fizzy and juice drinks.
A systematic review is the “gold standard” of assessing a body of previously published clinical evidence. It uses rigorous methods that enable researchers to identify and assess all relevant evidence on the issue.
What did the research involve?
The researchers set out to identify the association between the amount of sugar consumed and the level of dental decay. In particular, they searched for studies looking at the effect of, or link between, restricting sugar intake to:
- less than 10% of total calorie intake, compared with more than 10%
- less than 5% of total calorie intake, compared with 5-10%
The review covers what are called “free sugars”. These are sugars added to foods by the manufacturer or consumer, plus those naturally present in honey, syrup, fruit juices and fruit concentrates.
The researchers searched various literature databases for relevant studies published since 1950 in any language. They included clinical trials that looked at the effect on dental caries of diets containing different sugar content that had a timescale of at least one year.
They also included observational studies that reported changes in sugar intake and information about dental decay. Participants in the studies were from all over the world and in all age groups.
The papers were assessed twice to see if they met review criteria. Researchers graded the quality of the studies as high, moderate, low or very low using an internationally accepted and validated system called GRADE. GRADE takes into account factors such as the consistency of results across available studies, the size of the effect, the evidence of a dose response and the strength of the association.
From 5,990 papers identified, the researchers included 55 studies that met the study criteria, 50 of them conducted in children. They did not identify any randomised controlled trials (RCTs). This is probably because randomising an individual to consume levels of sugar that could potentially be harmful would be considered unethical by most research institutes.
What were the basic results?
The full results of each of the identified studies are extensive and cannot be summarised here.
The overall results were:
- 42 out of 50 of the studies in children, and 5 out of 5 in adults, reported at least one positive association between sugars and dental decay
- there was “moderate quality” evidence showing a lower risk of dental decay when sugar intake is less than 10% of calorie intake, compared with more than 10%
- there was “very low quality” evidence showing a lower risk of dental decay when sugar intake is less than 5%, compared with 5-10% of calorie intake
How did the researchers interpret the results?
The researchers say that dental decay progresses with age and the effects of sugars are lifelong. Even low levels of decay in children are of significance throughout life, they add.
While the evidence for a limit of 10% less sugar intake is moderate, they suggest there “may be benefit in limiting sugars to less than 5% to minimise the risk of dental caries throughout the life course”.
They also point out that while fluoride has a protective role, the association between sugar and dental caries remains.
In an accompanying press release, one of the study’s authors, Paula Moynihan, Professor of Nutrition and Oral Health at Newcastle University, said: “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 throughout life.
“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.
“Part of the problem is that sugary foods and drinks are now staples in many people’s diet in industrialised countries, whereas once they were an occasional treat for a birthday or Christmas. We need to reverse this trend.”
This was a systematic review that considered all the evidence on the relationship between dental decay and sugar intake dating back more than 60 years.
It is worth noting that the researchers did not identify any randomised controlled trials – the gold standard of clinical evidence – on the issue.
However, given the detrimental effect that a high sugar intake is known to have on health, there are likely to be practical and ethical issues around randomising people to long-term intakes of high or low added sugar purely to look at who was more likely to develop tooth decay.
That said, the review is a timely reminder that sugar intake is associated with dental decay and that this association remains despite the introduction of fluoride toothpaste and, in some countries, fluoridated water. It would not be safe to assume that access to a fluoridated water supply means you can have your fill of sweet foods.
The evidence for lowering sugar intake to less than 5% of calorie intake came from three population surveys carried out in Japan in 1959 and 1960, and is considered very low quality. It is therefore debatable whether current advice will be altered.
Sugary foods and drinks not only cause tooth decay, they are high in calories and can contribute to people’s risk of diabetes and being overweight or obese.
The current advice is to limit your added sugar intake to 10% or less of calories a day. That’s about 70g of sugar for men and 50g for women, although this will vary according to factors such as size, age and how active people are.
Foods and drinks high in sugar should only be consumed in small amounts. For more advice about sugar intake, see How much sugar is good for me?