In Australia, the caries experience of 6-year-old and 12-year-old children has increased since the mid to late 1990s.1 Caries rates had declined previously, attributable to community water fluoridation. The recent caries increase has been attributed speculatively to changes in fluid intake, including increased consumption of sweet drinks and bottled waters.2–6
Australian children have ready access to a wide variety of drinks in the home, school and community. Societal changes, such as increasing urbanization and globalization, have altered children’s diets worldwide, promoting availability and access to fast foods, processed foods and sweet drinks.7–11 This increased consumption is of concern to the health profession and may reflect extensive advertising of sweet drinks during children’s television shows in many countries, including Australia.4,12–16 The beverage industry has reported increased sales of bottled water,17 but there are no data to indicate children are drinking this in preference to tap water. Anecdotal reports linking increased caries prevalence and bottled water consumption are speculative. This review addresses fluid intakes and caries risk of Australian children, with emphasis on the role of sweet drinks in caries.
Consumption of water
In Australia, fluoridated reticulated drinking water is available in many areas, providing caries prevention to individuals of all ages and socio-economic status.18–21 In the absence of fluoridated water, caries experience of children has increased. An Australian dental health survey conducted in 2002 reported children residing in areas where the water contained negligible fluoride had poorer dental health than those residing in optimally fluoridated areas, regardless of socio-economic disadvantage or residence.22 Data collected in Victoria in 2002 found 5–6 year old and 11–12 year old children without access to fluoridated water had 60% and 42% higher dmft/DMFT scores respectively, than those with access to fluoridated water.23
Bottled water is readily available in Australia but typically does not contain optimal fluoride for caries prevention.24 The fluoride content is not labelled on most bottled waters. A study of several bottled waters purchased from local supermarkets in 2004 showed the fluoride content was less than 0.08 ppm.24 In 2009, the regulatory committee of Food Standards Australia New Zealand approved the addition of fluoride to non-carbonated bottled water to levels of 0.6–1.0 mg/L, mandating package labelling to inform consumers that fluoride had been added.25 Media reports indicate that sales and consumption of bottled water have increased in Australia and globally over the past decade,17,26 and it is speculated that regular intake of non-fluoridated bottled water instead of fluoridated water may increase an individual’s caries risk.24
The National Health and Medical Research Council in Australia recommends an average person in a mild climate should drink about one and a half litres of fluids per day.27 The 1995 Australian National Nutrition Survey (1995 ANN Survey) found the daily water intake was approximately 600 mL for 4–11 year olds.28 A parent questionnaire in 2009 of 266 primary school children in Melbourne estimated the mean fluid intake on the day previous to the study day was 1.5 ± 0.5L.29
Consumption of sweet drinks, juices and milk by children
In Australia, ‘energy-dense’ drinks contain added sugars or sugars from fruit.28 The term is comparable to ‘non-milk extrinsic sugars’ as used in the United Kingdom (UK), and to ‘free sugars’– the equivalent term used by the World Health Organization.30 Non-milk extrinsic sugars are the ‘sugars found in confectionery, soft drink, table sugar, biscuits, cakes, fruit juices, honey and sugars added to recipes’.31 Consumption of non-milk extrinsic sugars is implicated as a significant risk factor in dental caries.31–33 Soft drinks, confectionery, biscuits and cakes are the main sources of non-milk extrinsic sugars for most of the population.30,33–35
Carbonated soft drinks contribute considerably to children’s total sugar intake in many countries.30,34,36–41 In the UK, soft drink intake in 11–12 year olds has increased in the last 20 years.30,42 In 2000, the most reported form of added sugars in the US diet was regular soft drink, accounting for one-third of sugar intake.37 A 2002 US study reported 504 children in grades 4–6 found soft drinks and fruit-flavoured drinks comprised over 50% of their daily total fluid intake.43 The Iowa Fluoride Study (conducted 1993–2000) of 645 children aged 1–5 years found intake of added-sugar drinks (juice drinks, regular soft drink, powdered drinks, sports drinks) was associated inversely with diet quality and negatively with calcium intake.44 Similar shifts in fluid intake towards sweet drinks may be occurring in Australia.27
Changes in societal behaviours in the last 30 years have increased availability and access to fast food, processed foods and drinks; fewer meals are eaten together in families and there is an increasing reliance on meals eaten away from home. Analyses of data from the US Nationwide Food Consumption Survey (1977–1978), the Continuing Survey of Food Intakes by Individuals (CSFII, 1994–1996) and the Supplemental Children’s Surveys (1998), found an increasing proportion of children’s soft drink intake came from restaurants, fast food outlets and vending machines in the US.45 Of the 577 primary school children in the CSFII, 64.1% consumed soft drink daily, with 32.3% drinking 260 mL or more per day.46 In comparison, a 1999 mail-in questionnaire study of 560 American 8–13 year olds found only 30% drank soft drink daily.47 Despite similar sample sizes, the lower frequency may reflect the convenience sample studied and the method of data collection.
Media reports on the beverage industry indicated that the average annual soft drink intake by Australians increased from 47 litres per person in 1969,48 to 110 litres per person in 2003.49 One-third of consumers represented nearly 70% of the total volume of soft drink sold in 1998,50 indicating that only a small proportion of Australians consumed a large proportion of the soft drinks sold. A 2006 media report indicated that almost 80% of 12–17 year olds consumed sugared soft drink weekly, with 10% drinking over one litre daily and 35% drinking 750 mL (two cans) daily; only 18% did not consume soft drink regularly.51 A parent questionnaire in 2009 of 266 primary school children in Melbourne found that sweet drinks comprised over 50% of their daily fluid intake for 7.5% of 4–7 year olds and 11.3% of 8–12 year olds.29
Soft drinks have minimal nutritional value, contain high amounts of sugar, and are classed as an ‘extra food’ to be consumed only occasionally or in small amounts.27 The 1995 ANN Survey reported a mean daily soft drink intake of approximately 130 mL for Australian children; approximately 9% of the daily sugar intake of 2–11 year olds came from soft drinks.28 A report based on this survey concluded that energy-dense drinks were over-represented in Australian schools, with children purchasing food from school canteens obtaining more energy from ‘junk food’ than non-canteen users.52 A cross-sectional survey of 1681 primary school-aged children in south-western Victoria studied food and drink intake at school during 2003–2004, and found that one-third of children drank fruit juice or cordial and another one-third drank water at school.53 Children from low socio-economic backgrounds were significantly more likely to receive more energy from juice, cordial or soft drinks than those from high socio-economic backgrounds.53 These reports highlight the importance of providing healthy foods and drinks for purchase at schools.
Media reports suggest some fruit juices sold in Australia contain more sugar than soft drinks.54,55 The Australian dietary guidelines recommend children consume two serves daily from the fruit group – with half a cup (125 mL) of fruit juice representing one serve, although juice should not substitute for fresh fruit.27 The mean daily intake of fruit juice of Australian children reported in the 1995 ANN Survey was over twice the RDI: 312 mL for 4–7 year olds and 278 mL for 8–11 year olds.28
Patterns of fluid intake have been reported recently for children in Melbourne. A 2003 study of 1560 Melbourne school children found 77% of 5–6 year olds and 81% of 10–12 year olds consumed at least one glass of juice, cordial or soft drink daily.56 A 2009 study of 266 primary school children in Melbourne used parental recall of fluid intake on the day previous to the study day as an indication of typical intake, and found that 90% of children had drunk tap water, 50% drank juice and 30% drank soft drink.29 Of concern, evening and/or night-time drink intake was reported for 78% of children, with 36% reporting drinking juices, cordials or soft drinks at these times.29
Cow’s milk is considered non-cariogenic, containing lactose (the least cariogenic mono- or disaccharide) and calcium, phosphate and casein which protect against demineralization.57–59 As the major dietary source, milk provided over 40% of calcium in 2–11 year old Australian children on the survey day of the 1995 ANN Survey.28 This survey noted a low intake of dairy products, with about 30% of 2–18 year olds consuming less than one serve of dairy product daily.28 The mean intake of milk reported for 4–7 year olds was 381.3 mL and 394.1 mL for those 8–11 year olds.28 The Australian dietary guidelines recommend two to three dairy product serves per day, including milk, for children aged 4–11 years and three to five serves per day for adolescents.27 Of concern, the parent questionnaire in the 2009 study of 266 primary school children in Melbourne found that 35% of 4–7 year olds and 26% of 8–12 year olds had not consumed any milk on the day previous to the study day.29
Are sweet drinks and juices displacing consumption of dairy products?
Age-related changes in fluid intake, shifting from dairy products to carbonated drinks, occur between childhood and adolescence.39,60,61 Children appear to be drinking soft drinks at a young age,62 and increase consumption through adolescence to young adulthood.11,39,42,63 Studying parental recall of fluid intakes on the day previous to the survey day of 266 primary school children in Melbourne in 2009, an intake shift was noted between younger and older children, from mostly water and milks (4–7 year olds) to a higher proportion of sweet drinks (8–12 year olds), evident in the proportion of those who had not consumed any sweet drinks (4–7 year olds: 35.0%; 8–12 year olds: 18.6%) and the proportion for whom sweet drinks comprised over 50% of their total fluid intake (4–7 year olds: 7.5%; 8–12 year olds: 11.3%).29
International reports also indicate a common trend of increasing consumption of regular and diet soft drink and decreasing consumption of dairy products among children, but the literature provides no consensus that carbonated drinks are actually displacing dairy product consumption by primary school-aged children. In the entire US population, soft drink intake has increased over the last two decades while dairy product consumption has declined.39,44–46,60,61,64–67 However, despite such reports, no correlation was seen between decreased calcium intake and soft drink consumption in adolescent girls using data from the US CSFII (1994–1996).68 Reporting an observational study of 268 children born in western Sydney (the Nepean Study), Tam et al. found increased sweet drink intakes did not displace milk consumption.69 But noting the already low milk intake of Australian children in the 1995 ANN Study,28 the increased sweet drink intake without milk displacement may actually reflect displacement of other fluids consumed, such as water.
Longitudinal studies are required to investigate any associations between high consumption of sweet drinks and inadequate dairy product intake in the Australian child population. Dietary inadequacy and increasing consumption of energy-dense drinks in Australia is of grave concern to health professionals due to the complex interactions between poor diet and systemic disease, and dental disease in particular.
Cariogenicity of sweet drinks and juices
Correlations between fluid intake and dental caries have been explored. Energy-dense drinks provide a carbohydrate metabolic substrate for cariogenic bacteria. Common fermentable carbohydrates in western diets are simple sugars (glucose, fructose, sucrose, maltose, lactose) found in foods and drinks. In the US, a can (345 mL) of regular soft drink is labelled to contain up to 11 teaspoons of sugar.70
Between-meal consumption and high intake frequency of sweet drinks increase their cariogenic potential.42,71 In comparison with periodic sipping, mealtime consumption of soft drinks is less harmful to the dentition.72,73 A Flemish study of 4468 children aged 7 years found daily consumption of sugared drinks and twice-daily between-meal intake of sugared snacks was associated with caries.74 The study recommended between-meal consumption of sugar-containing snacks and drinks should not exceed twice per day to prevent caries development in young children.74 A US epidemiological study found the frequency and amount of soft drink consumed between meals were associated significantly with high DMFT scores.75 Similarly, a US cross-sectional study of 306 children aged 1–5 years with and without caries experience concluded that the cariogenicity of a food or drink was more likely to be related to the frequency and duration of intake than the type of sugar in the product.71
An early review of the US National Health and Nutrition Examination Survey (NHANES I) data found no correlation between high DMFT scores and reported fruit juice intake of participants for the period 1971–1974.76 A later review of NHANES III data found an association between increased soft drink intake and increased DMFS in persons aged 25 years and older, but not in younger age groups.77 As those aged under 25 years in the NHANES III survey had received lifetime fluoride exposure, the caries potential of sweet drinks may have been modulated by fluoride protection.77
The association between caries and sweet drink intake by young children has been shown in several more recent US studies. A study conducted in 1993–2000 of 642 children aged 1–5 years found the regular intake of sugared soft drinks correlated with increased caries risk and was the strongest predictor of caries extent, whereas milk intake was ‘neutrally associated’ with caries.64 This was confirmed in a later survey (2002–2003) of 436 children aged 3–5 years from low-income households where soft drink intake was associated with higher dmft scores.40 A longitudinal study of preschoolers from low-income households found that those with high soft drink intake, or those whose intake had increased over a two-year period, were at higher caries risk.78
Recent studies from our research group have shown significant associations between sweet drinks consumption and caries in children and adolescents in small study populations in Melbourne and Vietnam.29,79 Studying the dietary habits and caries experience of 266 primary school children from low-income families residing in fluoridated Melbourne in 2009, caries observed clinically during the past 12 months was associated significantly (p = 0.004) with recalled evening and/or night-time consumption of sweet drinks on the previous day.29 Caries observed clinically in the past 24 months was associated significantly with increasing intake frequency of sweet drinks plus sweet foods (p = 0.001), and with increasing frequency of sweet foods (p = 0.006), on the previous day.29 A total of 389 children aged 11–16 years living in three non-fluoridated rural villages in Vietnam were examined during 2007–2009 as part of a humanitarian aid project.79 The children did not access regular dental care but participated in school-based fluoride toothpaste brushing programmes. Averaged across the three villages, the mean (± SD) caries experience increased with intake frequency of sweet drinks and sweet foods – sweet drinks: consumed twice/day, 4.2 (2.4); three or more times/day, 6.6 (2.0); sweet foods: consumed twice/day, 4.2 (2.6); three or more times/day, 4.8 (2.5); sweet drinks plus sweet foods: consumed three to four times/day, 4.4 (2.5); five or more times/day, 5.7 (2.5).79
The fluoride content of soft drinks is not labelled on products sold in Australia or the US. The fluoride content of soft drinks purchased in Iowa, USA in 1995–1997 was 0.02–1.28 ppm, with 71% of drinks sampled containing over 0.6 ppm fluoride.80 The variation was attributed to different water sources used at production sites. The fluoride content of fruit juice and juice-flavoured drinks available in Iowa was 0.02–2.80 ppm.81 Due to high fluoride levels in some soft drinks and juices, dietary fluoride supplementation for children consuming large volumes of these fluids in non-fluoridated areas has been cautioned against in the US.80,81 The fluoride levels of soft drinks and fruit juices in Australia have been reported to be less than that of fluoridated reticulated water,82 so children consuming these in large amounts and displacing other fluid intake may not receive the full benefit of water fluoridation.
In addition to promoting caries, sweet drinks can promote dental erosion. Most sweet drinks, including diet soft drinks, contain phosphoric, carbonic and citric acids. Malic, tartaric and other organic acids may also be present.70,73,83 Both regular and diet soft drinks have low pH (typically 2.4–3.5), high titratable acidity, and low calcium and phosphate concentrations, with the potential for erosion as well as cariogenicity.42,73 Juices, regular and diet soft drinks can erode enamel,73,84–86 and enamel dissolution by soft drink acids can exceed the effects of bacterial acids from metabolism of sugars in the drink.87 However, the potential of diet soft drinks (containing sugar substitutes) to increase caries risk is decreased markedly due to lack of sugar.88 The addition of 0.2% w/v casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) added to acidic drinks has been shown to reduce erosivity 89 but the effect on cariogenicity is yet to be examined.
A UK review in 2006 made valuable recommendations for ‘safe use’ of soft drinks: limit consumption to mealtimes; keep drinking times short; do not use soft drink in a nursing bottle; consume soft drink using a straw; consume soft drink chilled; do not swish or hold soft drink in the mouth; and avoid toothbrushing immediately after consumption.42 Appropriate recommendations for safer consumption of soft drinks must be advocated by health professionals and promoted to the community in order to advise regular consumers of the deleterious effects of these drinks on the dentition (Table 1).
|Consumption of sweet drinks|
|In general concerning sweet drinks||• Do not place in a baby’s nursing bottle |
• Restrict sales in schools
• Reduce overall consumption
• Increase consumption of fluoridated water
• Avoid consuming between meals
|If sweet drinks are consumed||• Limit consumption to mealtimes |
• Consume chilled rather than at room temperature
• Keep drinking times short
• Drink through a straw placed away from the teeth to reduce surface contact
• Avoid slow sipping, swishing or holding drink around the teeth
|After consuming sweet drinks||• Drink fluoridated water and rinse mouth with water |
• Avoid toothbrushing immediately after consumption to reduce removal of demineralized surface enamel
• Rinse teeth with a non-alcoholic, neutral pH fluoride mouthrinse to remineralize surface enamel
Sweet drinks and general health of children
A meta-analysis reported in 2007 indicated clear associations between soft drink intake, increased energy intake and increased body weight.65 As a health intervention to combat obesity, the sale of sweet drinks in Victorian government schools was banned in 2007. Regular sugared soft drinks can no longer be sold or consumed in these schools. Diet (low or no-sugar alternative) soft drinks are permitted, as are fruit juices (natural sugar content, no added sugar), and milk.51,90 At institution, the ban affected about 67% of all school students in Victoria.91 Private schools create their own policies regarding nutrition and canteen choices and were strongly urged to follow suit. The American Association of Pediatrics and the American Academy of Pediatric Dentistry have also recommended eliminating sweet drinks access in US elementary schools to prevent health problems related to overconsumption.92,93
A systematic literature review (to May 2005) found strong evidence linking the intake of sweet drinks, particularly soft drink, to childhood weight gain and obesity.38 Obese children and adolescents are at increased risk of sleep apnoea, mobility difficulties, diabetes and early development of risk factors for cardiovascular disease, and have greater risk of adult obesity and associated health risks.94,95 A US prospective study of 548 children found sweet drink intake was associated with obesity in 11–12 year olds; the obesity risk was estimated to rise 60% for each can of soft drink consumed daily.96 A two-year longitudinal cross-sectional study of 166 grade 3–5 children residing in Nebraska, USA found increased diet soft drink intake was associated with increased body mass index (BMI) scores.67
Amongst Australian children, similar associations have been noted between sweet drink intake and increasing body weight. One media report suggested that Australia has the fastest growing childhood obesity rate in the world.97 The 1995 ANN Survey investigated fluid intakes of 1496 children aged 5–12 years, separating ‘core’ (water, milk) and ‘non-core’ drinks (other).28 The children had a mean daily energy intake of 1552 kJ from drinks, with 30.8% of this coming from non-core drinks.98 Overweight or obese children tended to obtain more energy from non-core drinks than those in a healthy weight range.98 The 1995 ANN Survey also showed among 7–15 year olds, 20% of boys and 21.5% of girls were overweight or obese.99 A longitudinal study of 268 Australian children found no correlation between BMI and carbohydrate intake from fruit juice or milk, but soft drink or cordial intake at age 8 years was associated statistically with excess weight gain five years later.69 A study of 1944 children aged 4–12 years in south-western Victoria found those regularly drinking sweet drinks, and those who had drunk more than two serves of juice, cordial or soft drink on the day prior to the survey day, were twice as likely to be overweight or obese.100
Current research on associations between childhood obesity and caries suggests a relationship between obesity per se and increased caries prevalence.101 A US convenience sample of 178 children aged 8–11 years found no association between BMI and mean caries experience, but a statistically significant association between increasing BMI and caries incidence in first permanent molars.102 A recent study of 427 children in the Iowa Fluoride Study found a positive association between obesity and caries in those from families of low socio-economic status.103 However, regardless of obesity, low socio-economic status is a known caries risk factor.32,104
Intake of sweet drinks as a component of caries risk assessment in children
Caries risk assessment (CRA) examines the cariogenic risk factors for an individual.105,106 A dental risk factor has been described by Burt as ‘an environmental, behavioural or biological factor, confirmed by temporal sequence, usually in longitudinal studies, which, if present, directly increases the probability of a disease occurring’.107 Since CRA identifies an individual’s potential for developing caries at a given time, the assessment should be made regularly throughout life and risk management instituted accordingly.104,108,109
As a multifactorial disease, no single risk factor or combination of factors has been identified to predict future caries with both high positive predictive values and high negative predictive values. In addition to the presence of cariogenic bacteria in the dental biofilm, environmental risk factors such as diet, past caries experience, saliva, medical conditions and suboptimal fluoride exposure are implicated.32,105,106,108–113 Control of these risk factors can alter the ecology of the biofilm and the subsequent likelihood of caries. Dietary risk factors include the amount of sugars consumed, manner of consumption, frequency of exposure and retentiveness.31,114–116 The cariogenicity of sugar appears weaker in the post-fluoride era due to the protective benefit of fluoride from multiple sources, such that fluoride has raised the threshold of sugar exposure required to promote caries progression to cavitation.31,114,115,117 Although caries cannot be predicted with perfect sensitivity and specificity, sufficient is known of risk factors for CRA to be valuable in clinical practice and past caries experience remains the best predictor of future caries.32,104,107–110
Caries risk assessment is now the standard of care in paediatric dentistry, supporting individualized preventive programmes and restorative care specific to the child’s current needs and perceived risk, and advising parents of their child’s caries risk status.105–107,118,119 Caries risk assessment can assist in determining optimal management for each child including dietary guidance, remineralization approaches, placement of sealants and restorations, the frequency of diagnostic radiographs and recall appointments, and in identifying those for whom parental support in reducing risk factors is indicated.32,95,113,120,121 On a population basis, CRA can identify groups of children at high risk and action can be taken to optimize resource allocation in a public health system to prevent and treat caries.108,122,123
Several CRA tools have been developed recently which include simple dietary assessment. These include the Pediatric Risk Assessment Tool (PRAT),10 the CAT104 and a community screening model with a sensitivity/specificity of 82%/73%.123 Responding to increased soft drink intakes and decreased dairy product intakes in the US, the PRAT was developed at the University of Iowa in 2003.10 A parent questionnaire addresses recalled fluid intake over the past 24 hours, recording total intake, frequency and timing of intake, focusing particularly on evening/night-time consumption. Questions address between-meal intake of confectionery and baked starches, fluoride exposure, oral hygiene practices, recalled past caries, use of age-appropriate strength fluoride toothpaste, parental knowledge of fluoride toothpaste for caries prevention, and topical and systemic fluoride exposure as essential determinants of oral health.112 A clinical examination is not included. We have modified the PRAT for Australian children and found it easily understood, readily applied and completed by parents within a few minutes.29
The CAT was developed by the American Academy of Pediatric Dentistry in 2007–2008 to assist dental and non-dental personnel to determine caries risk of children.104 A parent questionnaire addresses the child’s past caries experience, current oral hygiene practices, fluoride exposure, diet, dental visit patterns, orthodontic appliances and socio-economic status of the family. The caries risk is then classified as low, moderate or high. Enabling use by non-dental personnel, the CAT does not use dental equipment but a ‘supplemental professional assessment’ can be added for clinicians to record visible plaque, gingivitis, enamel defects, radiographic information, periodontal scores and saliva tests. The CAT specifies a child’s caries risk is based on the single highest risk factor, so that a child categorized as high risk for one factor but low risk for all other factors is classified at high risk. A single high risk factor increases caries risk, regardless of the lack of co-existing risk factors. A US dental school study found the CAT was useful in prescribing radiographs and preventive procedures, and was readily completed by dental student clinicians.124 Used in combination when studying primary school children, we have found the PRAT and CAT could demonstrate statistically significant associations between caries experience and intake of sweet drinks and sweet treats, fluoride exposure, enamel demineralization and irregular dental care.29
Based on the above review, the following clinical recommendations are made: (1) the frequency and timing of drinking sweet drinks should be included in discussing dietary risk factors for dental caries and erosion with patients and parents; (2) caries risk assessment protocols should include assessment of sweet drink intake; (3) a child remaining at high caries risk despite the best efforts by the dental team may require referral to a dietitian for dietary counselling; and (4) health professionals should provide the community with appropriate recommendations and cautions concerning the consumption of sweet drinks, noting the potential for deleterious effects on the dentition.