After focusing on the reduction of intake of mainly saturated fatty acids for several decades, contemporary dietary advice also includes the reduction of added and free sugars for the prevention of obesity, diabetes, and related cardiovascular diseases. The most recent World Health Organization (WHO) guideline1 advocates to reduce free sugar consumption to below 10% of the energy intake (10 E%) or even below 5 E% of the diet. Free sugars are defined as all monosaccharides and disaccharides added to foods by the manufacturer, cook, or consumer, and sugars naturally present in honey, syrups, fruit juices, and fruit juice concentrates (Fig 4-1).1 Sugars in whole fruits and vegetables are excluded from this list probably due to the health benefits of the structure and bite, and other beneficial constituents. These benefits may be limited if the fruit or vegetables are crushed or squeezed. It is beyond debate that the consumption of sugar-containing foods imposes a risk on the integrity of our teeth. The WHO guideline to use less sugar may thus be an opportunity, and support dentistry, in collaboration with other health and nutrition authorities, in its goal to get the message across to the public of using less sugar in lower frequencies. As these are national collaborations, a prerequisite is that the national health and nutrition authorities are clear on their goals, and for the present in many countries the WHO guidelines are not (yet) adopted or translated exactly into the national recommendations. The Dutch dietary guidelines for the sensible use of sugars simply advise not to use products to which sugars are added, or products with free sugars as a result of processing. Furthermore, it is advised to drink as little as possible sugar-sweetened beverages (SSB) and to use whole grain products instead of refined grains.2,3 For combined general health and dental health strategies, the oral health benefits of these strategies should be guaranteed.
The actual oral health risk of a certain food is modulated by many factors, and these are divided into food-related factors and consumer-related factors. Food-related factors involve the release of the sugars, the stickiness of the product (although this may be less important at tooth sites where food is impacted), and, to a lesser extent, the type and concentration of the sugar. Consumer-related factors are the frequency of the consumption, the drinking and chewing habits, the chewing and swallowing efficiency, salivary flow and composition, the presence of cariogenic dental plaque, and the use of fluorides. It is a common observation that with a comparable number or amount of sugar-containing products, some people are able to manage the risk and will not develop caries, while others will develop significant amounts of dental caries. Advice aimed at some of the modulating factors may have a great impact on oral health without necessarily creating a reduction in the total sugar intake; for instance, suggestions to combine eating and drinking moments, avoid nightly consumption, or clean the mouth after consumption. On the other hand, this advice does not obstruct additional advice to limit the energy intake from free sugars to (below) 10 E%.
The two ways (as well as all combinations of these) to achieve a reduction of sugar consumption are a reduction of the amount of sugar in products, a strategy deployed by some retailers and manufacturers, or a reduction of the number or portions of consumptions of sugar-containing products, which hopefully may result in a reduction of the frequency of consumption. The latter strategy may be a topic of health education programs but may also be targeted by selective taxation measures to make unhealthy foods more expensive and healthy foods cheaper. To answer the question of how these strategies would impact oral health, the following six issues are of importance:
- the shape of the dose-response association between sugar intake and caries
- the influence of fluoridated toothpaste usage on the association of sugar intake and caries
- the relative contribution of frequency and amount of sugar intake to caries levels4
- whether, in relation to oral health, there is a safe amount of sugar in products
- the effectiveness of selective taxation
- the effectiveness of dietary advice in the dental office.
Any strategy has to be accepted by those that add the sugars to products (retailers and manufacturers) and by consumers of the products in a way that ensures a real reduction of sugar intake is accomplished.
In the late 1970s, before fluoride was widely used and when the quality of oral hygiene was generally poor, Sreebny5 compared caries prevalence among 12-year-old and 6-year-old children in 47 and 23 nations respectively, with the availability of sugar per capita. Regression analysis with these data revealed an increase of 1 decayed, missing, or filled tooth (DMFT) at the age of 12 for every 25 g of sugar availability per day, and an increase of 1 decayed, missing, or filled surface (dmfs) in the 6-year-olds for every 50 g of sugar available per day.5 Sreebny5 suggested that 18.25 kg (approximately 10 E%) per person per year may represent an upper limit of safe, or at least “acceptable” sugar consumption for oral health. Based on the data of Sreebny5 and the effect of the wartime diets,6 Sheiham7,8 suggested that the relationship between sugar intake and caries levels is sigmoid. Sheiham7,8 claimed that below approximately 15 kg/person/year most of the population will not develop dental caries. Between 15 and 35 kg there is a steep increase in the rate of caries. Beyond 35 kg the dose-response curve flattens. In many western societies the sugar availability is around or above 40 kg/person/year.
A sigmoid relationship between sugar intake and caries would explain why the relatively small differences in sugar consumption between persons in these high-sugar societies are not necessarily reflected in differences in caries experience. No other studies, however, have confirmed the sigmoid curve. Most studies found no, a linear, or a log-linear relationship between sugar availability or consumption and caries.
In more recent studies in countries where fluoride supplements were widely used, the relationship between sugar availability and caries was less clearly observed. Woodward and Walker9 studied the relationship in 61 developing countries and 29 industrialized countries. In the developing countries, approximately 26% of the variation in the caries data was explained by sugar availability. In the industrialized countries, less than 1% was explained, while the slope of the linear regression line was estimated to be −0.013, not significantly different from zero. These data suggest that, where fluoride is available, variation in the availability of sugar may be of lesser importance as a determinant of caries prevalence and severity. Ruxton et al10 used data from Sreebny5 and Woodward and Walker9 to inventory sugar availability and dental caries in more than 60 countries in the 1970s and 1980s to assess the relation between caries rates and the sugar supply. In 18 countries, both DMFT and the sugar supply declined, whereas in 25 countries DMFT declined and sugar supply increased. In another 18 countries, the incidence of caries and the sugar supply increased. The authors concluded that the relationship between sugar reduction and caries on a nationwide basis was unreliable. Downer et al11 reported that dental caries experience (DMFT) of 12-year-old children in 29 countries of Europe yielded a strong negative correlation with sugar disappearance (r = −0.561, P < .01). The authors suggested the possible explanation that the extensive use of (mainly fluoride-containing) toothpaste neutralizes the potential damage from high sugar consumption.11 A recent global evaluation confirmed that amongst high income countries there is a negative correlation between sugar disappearance (kg/capita/year) and dental caries level, while in low income countries this correlation is a positive one.12 In the ensuing discussion Masood et al12 explained their findings also by the accessibility of fluoride.
Burt and Pai13 reported that, of the 69 studies on diet and caries published between January 1980 and July 2000, only two showed a strong diet-caries relation. Of the other studies, 16 showed a moderate relation and 18 showed a weak relation. They emphasized that the findings of their review differed from sugar-caries studies published in the decades before fluoride use. They concluded that sugar consumption is still likely to be a more powerful indicator for risk of caries infection in persons that don’t have regular exposure to fluoride.
Out of 10 epidemiologic studies published between 1995 and 2006, five found no association, one a positive association, and four a complex association meaning statistically significant association in certain subgroups between the use of sugars and caries.14 The subgroups in which the association was demonstrated were the groups who brushed their teeth once a day or less. An example of a study with a complex outcome was the cross-sectional National Diet and Nutrition Survey of children aged 1.5 to 4.5 years.15 Caries was associated with sugar confectionary (amount and frequency) but only in children of nonmanual-labor households whose teeth were brushed less than twice a day.
The importance of fluoride use on the relationship between sugar intake and caries is also confirmed by the fact that in spite of the dramatic decline in dental caries prevalence that occurred in the 1970s to 1990s in most Western industrialized countries, sugar consumption remained virtually unchanged.16,17
The low correlation between sugar consumption (disappearance, calculated according to production and sales) and caries prevalence when fluoride is used, indicates that proper use of fluoridated toothpaste has a major preventive effect on caries prevalence, although this protection is not easily achieved by everyone or at every site in the mouth. The low correlation is no license to disregard reduction of sugar intake as a caries preventive measure, but during dietary counselling, the paramount importance of fluoride should always be stressed.
Rugg-Gunn et al18 showed that the bivariate correlations with caries were higher when the sugar variables were calculated for snacks alone than for all intakes. Burt et al19 showed the energy from total sugars and meal sugars was not significantly different between low caries children and high caries children, but the energy from snacks, snack carbohydrate, and snack sugars were different. Both studies may confirm the conclusions of the Vipeholm study that in-between meal snacking is a great risk for caries development, while as much as 300 g additional sugar during the mean meals is not.20
Bernabé et al4 showed in Finnish adults that DMFT increased over a period of 4 to 11 years by 0.15 and 0.1 units for every additional occasion of sugar consumption and every additional 10 g of sugars consumed, respectively. In the mutually adjusted model, only the amount of sugar remained significantly associated with DMFT levels although the coefficient was reduced to 0.09. When the population was divided in those who used fluoride daily vs those who used it less frequently, the coefficient for amount was 0.08 and for frequency 0.12 for the frequent fluoride users, and 0.26 and 0.43 at infrequent fluoride use.
Dusseldorp et al21 dichotomized the number of eating moments as more than 7 a day vs less than 7 a day, which is the nationally recommended maximum frequency of food and drinks consumption per day in the Netherlands. With this dichotomization the number of foods and drinks consumed per day had impact on caries prevalence in the primary teeth of 9-year-olds (odds ratio [OR] 2.78, 95% confidence interval [CI] 1.21 to 6.40), but not on the caries experience in the permanent teeth of 9-year-olds (OR 0.97, 95% CI 0.65 to 1.44) or prevalence and experience in the permanent dentition of 15- or 21-year-olds. The authors concluded that the used number of eating moments is an appropriate cut-off point for recommendation.
A study conducted in nursery homes showed that 3-year-old low socioeconomic schoolchildren with the highest frequency of sugar consumption (4 ± 5 times per day) at the nursery were 4.7 times more likely to have a high caries increment over 1 year, compared to those with the lowest frequency (1 ± 2.9 times per day) (OR 4.7, 95% CI 2.7 ± 8.2, P < .001). Daily frequency of sugar intake at the nursery showed a dose-response trend with the risk of having high caries increment.22 Feldens et al23 studied the relationship between feeding practices in the first year of the life and the occurrence of severe early childhood caries (S-ECC) at 4 years of age. A total of 340 children were examined. The multivariable model showed a higher adjusted risk of S-ECC for the following dietary practices at 12 months: daily breastfeeding frequency at 12 months 0 to 2, 3 to 6, or ≥ 7 times showed relative risk (RR) values of 1.00, 2.04 (95% CI 1.22 to 3.39), and 1.97 (95% CI 1.45 to 2.68, P < .001), respectively; number of daily meals and snacks at 12 months < 7, 7 to 8, > 8 showed RR values of 1.00, 0.99 (95% CI 0.70 to 1.39), and 1.42 (95% CI 1.02 to 1.97, P = .025); bottle use for fruit juices/soft drinks at 12 months “no/yes” demonstrated a RR of 1.41 (95% CI 1.08 to 1.86) for the users (P = .025); high-density sugar foods at 12 months (> 50% of simple carbohydrates in unit of food) “no/yes” gave a RR of 1.43 (95% CI 1.08 to 1.89, P = .003); bottle use for liquids other than milk showed a RR of 1.41 (95% CI 1.08 to 1.86).
The studies of Rodrigues and Sheiham22 and Feldens et al23 strongly indicated that the increased frequency of sugary foods imposed caries risk in the low socioeconomic populations studied. Thus, all these data still support the scientific basis for dental health professionals to focus their dietary advice on reducing the frequency of intake of sugars.
Also, the type of products, SSB, and fruit drinks, sweets, and candy, and sugared dairy products contributing to the intake of sugar24 lend themselves to skiping, combining, or reducing the moments of intake.