5. Population nutrient intake goals for preventing diet-related chronic diseases:
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Numerous cross-sectional epidemiological studies have compared sugars intake with dental caries levels in many countries of the world. Those conducted before the early 1990s have been summarized by Rugg-Gunn (21). Nine out of 21 studies that compared amount of sugars consumed with caries increment found significant associations, while the other 12 did not. Moreover, 23 out of 37 studies that investigated the association between frequency of sugars consumption and caries levels found significant relationships, while 14 failed to find any such associations.
A cross-sectional study in the United States of 2514 people aged 9-29 years conducted between 1968 and 1970 found that the dental caries experience of adolescents eating the highest amounts of sugars (upper 15% of the sample) was twice that of those eating the lowest amounts (lower 15% of the sample) (52). Granath et al. (53) showed that intake of sugars was the most important factor associated with caries in the primary dentition of preschool children in Sweden. When the effects of oral hygiene and fluoride were kept constant, the children with a low intake of sugars between meals had up to 86% less caries than those with high intakes of sugars. Other studies have found fluoride exposure and oral hygiene to be more strongly associated with caries than sugars consumption (54, 55). A recent study in the United Kingdom of a representative sample of children aged 4-18 years showed no significant relationship between caries experience and level of intake of free sugars; in the age group 15-18 years, however, the upper band of free sugars consumers were more likely to have decay than the lower band (70% compared with 52%) (20).
Many other cross-sectional studies have shown a relationship between sugars consumption and levels of caries in the primary and/or permanent dentitions in countries or areas throughout the world, including China (56), Denmark (57), Madagascar (58, 59), Saudi Arabia (60), Sweden (61, 62), Thailand (63) and the United Kingdom (64).
When investigating the association between diet and the development of dental caries it is more appropriate to use a longitudinal study design in which sugars consumption habits over time are related to changes in dental caries experience. Such studies have shown a significant relationship between caries development and sugars intake (65-67). In a comprehensive study of over 400 children in England aged 11-12 years, a small but significant relationship was found between intake of total sugars and caries increment over 2 years (r = +0.2) (67). The Michigan Study in the United States investigated the relationship between sugars intake and dental caries increment over 3 years in children initially aged 10-15 years (66). A weak relationship was found between the amount of dietary sugars consumed and dental caries experience.
In a review of longitudinal studies, Marthaler (68) analysed the relationship between dietary sugars and caries activity in countries where the availability of sugars is high and the use of fluoride is extensive. He concluded that in modern societies that make use of prevention, the relationship between sugars consumption and dental caries was still evident (68). He also concluded that many older studies had failed to show a relationship between sugars intake and development of dental caries because they were of poor methodological design, used unsuitable methods of dietary analysis or were of insufficient power (68). Correlations between individuals’ sugars consumption and dental caries increments may be weak if the range of sugars intake in the study population is small. That is to say, that if all people within a population are exposed to the disease risk factor, the relationship between the risk factor and the disease will not be apparent (69).
Frequency and amount of sugars consumption. Several studies, including the above-mentioned Vipeholm study in Sweden, have indicated that caries experience increases markedly when the frequency of sugars intake exceeds four times a day (50, 70-72). The importance of frequency versus the total amount of sugars is difficult to evaluate as the two variables are hard to distinguish from each other. Data from animal studies have indicated the importance of frequency of sugars intake in the development of dental caries (73, 74). Some human studies have also shown that the frequency of sugars intake is an important etiological factor for caries development (75). Many studies have related the frequency of intake of sugars or sugars-rich food to caries development but have not simultaneously investigated the relationship between amount of sugars consumed and dental caries, and therefore no conclusion regarding the relative importance of these two variables can be drawn from these studies (76-78).
Animal studies have also shown a relationship between amount of sugars consumed and the development of dental caries (79-82). Several longitudinal studies in humans have indicated that the amount of sugars consumed is more important than the frequency (66, 67, 83, 84), while Jamel et al. (85) found that both the frequency and the amount of sugars intake are important.
The strong correlation between both the amount and frequency of sugars consumption has been demonstrated by several investigators in different countries (67, 86-88). It is therefore highly likely that, in terms of caries development, both variables are potentially important.
Relative cariogenicity of different sugars and food consistency. Therelative acidogenicity of different monosaccharides and disaccharides has been investigated in plaque pH studies, which have shown that lactose is less acidogenic than other sugars (89). Animal studies have provided no clear evidence that, with the exception of lactose, the cariogenicity of monosaccharides and disaccharides differs. The above-mentioned study in Turku, Finland, found no difference in caries development between subjects on diets sweetened with sucrose compared with those whose diet had been sweetened with fructose (51). Invert sugar (50% fructose + 50% glucose) is less cariogenic than sucrose (90).
The adhesiveness or stickiness of a food is not necessarily related to either oral retention time or cariogenic potential. For example, consumption of sugars-containing drinks (i.e. non-sticky) is associated with increased risk of dental caries (85, 88).
Potential impact of sugars reduction on other dietary components. It is important to consider the potential impact of a reduction in free sugars on other components of the diet. Simple, cross-sectional analysis of dietary data from populations has shown an inverse relationship between the intake of free sugars and the intake of fat (91), suggesting that reducing free sugars might lead to an increase in fat intake. There is, however, a growing body of evidence from studies over time that shows that changes in intake of fat and free sugars are not inversely related, and that reductions in intake of fat are offset by increases in intakes of starch rather than free sugars (92, 93). Cole-Hamilton et al. (94) found that the intake of both fat and added sugars simultaneously decreased as fibre intake increased. Overall dietary goals that promote increased intake of wholegrain staple foods, fruits and vegetables and a reduced consumption of free sugars are thus unlikely to lead to an increased consumption of fat.
Influence of fluoride. Fluoride undoubtedly protects against dental caries (95). The inverse relationship between fluoride in drinking-water and dental caries, for instance, is well established. Fluoride reduces caries in children by between 20% and 40%, but does not eliminate dental caries altogether.
Over 800 controlled trials of the effect of fluoride administration on dental caries have been conducted; collectively these studies demonstrate that fluoride is the most effective preventive agent against caries (95). Several studies have that indicated that a relationship between sugars intake and caries still exists in the presence of adequate fluoride exposure (33, 71, 96, 97). In two major longitudinal studies in children, the observed relationships between sugars intake and development of dental caries remained even after controlling for use of fluoride and oral hygiene practices (66, 67). As mentioned earlier, following a review of available longitudinal studies, Marthaler (68) concluded that, even when preventive measures such as use of fluoride are employed, a relationship between sugars intake and caries still exists. He also stated that in industrialized countries where there is adequate exposure to fluoride, no further reduction in the prevalence and severity of dental caries will be achieved unless the intake of sugars is reduced.
A recent systematic review that investigated the importance of sugars intake in caries etiology in populations exposed to fluoride concluded that where there is adequate exposure to fluoride, sugars consumption is a moderate risk factor for caries in most people; moreover sugars consumption is likely to be a more powerful indicator for risk of caries in persons who do not have regular exposure to fluoride. Thus, restricting sugars consumption still has a role to play in the prevention of caries in situations where there is widespread use of fluoride but this role is not as strong as it is without exposure to fluoride (98). Despite the indisputable preventive role of fluoride, there is no strong evidence of a clear relationship between oral cleanliness and levels of dental caries (99-100).
Excess ingestion of fluoride during enamel formation can lead to dental fluorosis. This condition is observed particularly in countries that have high levels of fluoride in water supplies (95).
Starches and dental caries
Epidemiological studies have shown that starch is of low risk to dental caries. People who consume high-starch/low-sugars diets generally have low levels of caries, whereas people who consume low-starch/highsugars diets have high levels of caries (39, 48, 49, 51, 67, 101, 102). In Norway and Japan the intake of starch increased during the Second World War, yet the occurrence of caries was reduced.
The heterogeneous nature of starch (i.e. degree of refinement, botanical origin, raw or cooked) is of particular relevance when assessing its potential cariogenicity. Several types of experiment have shown that raw starch is of low cariogenicity (103-105). Cooked starch is about onethird to one-half as cariogenic as sucrose (106, 107). Mixtures of starch and sucrose are, however, potentially more cariogenic than starch alone (108). Plaque pH studies, using an indwelling oral electrode, have shown starch-containing foods reduce plaque pH to below 5.5, but starches are less acidogenic than sucrose. Plaque pH studies measure acid production from a substrate rather than caries development, and take no account of the protective factors found in some starch-containing foods or of the effect of foods on stimulation of salivary flow.
Glucose polymers and pre-biotics are increasingly being added to foods in industrialized countries. Evidence on the cariogenicity of these carbohydrates is sparse and comes from animal studies, plaque pH studies and studies in vitro which suggest that maltodextrins and glucose syrups are cariogenic (109-111). Plaque pH studies and experiments in vitro suggest that isomalto-oligosaccharides and gluco-oligosaccharides may be less acidogenic than sucrose (112-114). There is, however, evidence that fructo-oligosaccharides are as acidogenic as sucrose (115, 116).
5. Population nutrient intake goals for preventing diet-related chronic diseases:
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