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5. Population nutrient intake goals for preventing diet-related chronic diseases: Previous page | 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27

Fruit and dental caries

As habitually consumed, there is little evidence to show that fruit is an important factor in the development of dental caries (67, 117-119). A number of plaque pH studies have found fruit to be acidogenic, although less so than sucrose (120-122). Animal studies have shown that when fruit is consumed in very high frequencies (e.g. 17 times a day) it may induce caries (123, 124), but less so than sucrose. In the only epidemiological study in which an association between fruit consumption and DMFT was found (125), fruit intakes were very high (e.g. 8 apples or 3 bunches of grapes per day) and the higher DMFT in fruit farm workers compared with grain farm workers arose solely from differences in the numbers of missing teeth.

Dietary factors which protect against dental caries

Some dietary components protect against dental caries. The cariostatic nature of cheese has been demonstrated in several experimental studies (126, 127), and in human observational studies (67) and intervention studies (128). Cow’s milk contains calcium, phosphorus and casein, all of which are thought to inhibit caries. Several studies have shown that the fall in plaque pH following milk consumption is negligible (129, 130). The cariostatic nature of milk has been demonstrated in animal studies (131, 132). Rugg-Gunn et al. (67) found an inverse relationship between the consumption of milk and caries increment in a study of adolescents in England. Wholegrain foods have protective properties; they require more mastication thereby stimulating increased saliva flow. Other foods that are good gustatory and/or mechanical stimulants to salivary flow include peanuts, hard cheeses and chewing gum. Both organic and inorganic phosphates (found in unrefined plant foods) have been found to be cariostatic in animal studies, but studies in humans have produced inconclusive results (133, 134). Both animal studies and experimental investigations in humans have shown that black tea extract increases plaque fluoride concentration and reduces the cariogenicity of a sugars-rich diet (135, 136).

Breastfeeding and dental caries

In line with the positive health effects of breastfeeding, epidemiological studies have associated breastfeeding with low levels of dental caries (137, 138). A few specific case studies have linked prolonged ad libitum and nocturnal breastfeeding to early childhood caries. Breastfeeding has the advantage that it does not necessitate the use of a feeder bottle, which has been associated with early childhood caries. A breastfed infant will also receive milk of a controlled composition to which additional free sugars have not been added. There are no benefits to dental health of feeding using a formula feed.

Dental erosion

Dental erosion is the progressive irreversible loss of dental hard tissue that is chemically etched away from the tooth surface by extrinsic and/or intrinsic acids by a process that does not involve bacteria. Extrinsic dietary acids include citric acid, phosphoric acid, ascorbic acid, malic acid, tartaric acid and carbonic acid found, for example, in fruits and fruit juices, soft drinks and vinegar. Erosion in severe cases leads to total tooth destruction (139). Human observational studies have shown an association between dental erosion and the consumption of a number of acidic foods and drinks, including frequent consumption of fruit juice, soft drinks (including sports drinks), pickles (containing vinegar), citrus fruits and berries (140-144). Age-related increases in dental erosion have been shown to be greater in those with the highest intake of soft drinks (20). Experimental clinical studies have shown that consumption of, or rinsing with, acidic beverages significantly lowers the pH of the oral fluids (121). Enamelis softened within one hour of exposure to cola but this may be reversed by exposure to milk or cheese (145, 146). Animal studies have shown that fruit and soft drinks cause erosion (124, 147), although fruit juices are significantly more destructive than whole fruits (148, 149).

5.6.4 Strength of evidence

The strength of the evidence linking dietary sugars to the risk of dental caries is in the multiplicity of the studies rather than the power of any individual study. Strong evidence is provided by the intervention studies (50, 51) but the weakness of these studies is that they were conducted in the pre-fluoride era. More recent studies also show an association between sugars intake and dental caries albeit not as strong as in the prefluoride era. However, in many developing countries people are not yet exposed to the benefits of fluoride.

Cross-sectional studies should be interpreted with caution because dental caries develop over time and therefore simultaneous measurements of disease levels and diet may not give a true reflection of the role of diet in the development of the disease. It is the diet several years earlier that may be responsible for current caries levels. Longitudinal studies (66, 67) that have monitored a change in caries experience and related this to dietary factors provide stronger evidence. Such studies have been conducted on populations with an overall high sugars intake but a low interindividual variation; this may account for the weak associations that have been reported.

The studies that overcome the problem of low variation in consumption of sugars are studies that have monitored dental caries following a marked change in diet, for example, those conducted on populations during the Second World War and studies of populations before and after the introduction of sugars into the diet. Such studies have shown clearly that changes in dental caries mirror changes in economic growth and increased consumption of free sugars. Sometimes changes in sugars consumption were accompanied by an increase in other refined carbohydrates. There are, however, examples where sugars consumption decreased and starch consumption increased yet levels of dental caries declined.

Strong evidence of the relationship between sugar availability and dental caries levels comes from worldwide ecological studies (26, 28). The limitations of these studies are that they use data on sugar availability and not actual intake, they do not measure frequency of sugars intake, and they assume that level of intake is equal throughout the population. Also, the values are for sucrose, yet many countries obtain a considerable amount of their total sugars from other sugars. These studies have only considered DMFT of 12-year-olds, not always from a representative sample of the population.

Caution needs to be applied when extrapolating the results of animal studies to humans because of differences in tooth morphology, plaque bacterial ecology, salivary flow and composition, and the form in which the diet is provided (usually powdered form in animal experiments). Nonetheless, animal studies have enabled the effect on caries of defined types, frequencies and amounts of carbohydrates to be studied.

Plaque pH studies measure plaque acid production, but the acidogenicity of a foodstuff cannot be taken as a direct measurement of its cariogenic potential. Plaque pH studies take no account of protective factors in foods, salivary flow and the effects of other components of the diet. Many of the plaque pH studies that show falls in pH below the critical value of 5.5 with fruits and cooked starchy foods have been conducted using the indwelling electrode technique. This electrode is recognized as being hypersensitive and non-discriminating, tending to give an “all or nothing” response to all carbohydrates (150).

Research has consistently shown that when annual sugar consumption exceeds 15 kg per person per year (or 40 g per person per day) dental caries increase with increasing sugar intake. When sugar consumption is below 10 kg per person per year (around 27 g per person per day), levels of dental caries are very low (26, 28, 29, 51, 151-158). Exposure to fluoride (i.e. where the proportion of fluoride in drinking-water is 0.7-1.0 ppm, or where over 90% of toothpastes available contain fluoride) increases the safe level of sugars consumption.

Tables 14-17 summarize the evidence relating to diet, nutrition and dental diseases.

Table 14. Summary of strength of evidence linking diet to dental caries

Evidence

Decreased risk

No relationship

Increased risk

Convincing

Fluoride exposure (local and systematic)

Starch intake (cooked and raw starch foods, such as rice, potatoes and bread; excludes cakes, biscuits and snacks with added sugars)

Amount of free sugars
Frequency of free sugars

Probable

Hard cheese
Sugars-free chewing gum

Whole fresh fruit


Possible

Xylitol
Milk
Dietary fibre


Undernutrition

Insufficient

Whole fresh fruit


Dried fruits

5. Population nutrient intake goals for preventing diet-related chronic diseases: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 | Next page

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