Added sugars and their impact on dental caries: A narrative review

Introduction

Added sugar consumption has hiked up over recent decades.¹ Owing to the development of new energy resources and the use of food processing technology, the global nutrition transition proclaims the swap from a conventional diet to a highly processed diet with excess sugar, fat, and salt.^1,2 As defined by the United States (US) Department of Agriculture, added sugars are either pure sugars or natural products with high sugar content that are added to food during processing or preparation.³ It has certain properties that make it suitable for use in the food industry such as a sweetening agent, flavor blender, modifier, texture, bodying agent, lubrication, caramelization, and bulking agent.⁴ World Health Organization (WHO) has recommended limiting the intake of sugars to less than 10% of total energy intake.⁵

Sugars add to the total energy density of diets.⁶ There is apprehension, that the intake of sugars especially in the form of sugar-sweetened beverages (SSB) raises the overall energy intake thereby reducing the intake of nutritious foods with adequate calories leading to an unhealthy diet.⁶ The rising trends in the consumption of SSBs and carbonated drinks especially among the younger age groups have been associated with many adverse health outcomes.⁷

Added sugar is a notable risk factor for adverse oral health as they are highly acidic contributing to the development of dental caries.⁷ In the event of dental caries, free sugars or added sugars are a critical dietary element.⁵ A dose-response relationship exists between the frequency of added sugar intake especially sugar sweetened beverages and subsequent increment in dental caries.8 This review aims to discuss the various sources and forms of added sugar intake, their impact on general health, their role in dental caries and its cariogenicity, barriers in addressing added sugar intake, clinical strategies, and policy measures.

Sources of added sugar intake

Sugar is found in a variety of forms, such as naturally occurring food (honey, fruits, and dairy products), processed food with added sugar, and drugs.⁹ More than 70% of sugar calories come from food products and beverages pre-sweetened by the food processor.¹⁰ They are also present in foods and drinks deemed to be nutritious, such as fruit juices and dried fruit. Fruit concentrate or other free sugars may be added in products that asseverate to have ‘no added sugar’.¹¹

Sugars are used while baking or cooking in the preparation of food products.³ Sugar and chocolate confectioneries, cakes, cookies, fruit pies, puddings, sugared cereals, jams, ice cream, fruit in syrup, smoothies, sugared soft drinks, sugared milk-based beverages, and sugar containing alcoholic beverages are some examples of food and drinks containing added sugars.¹² Further, added sugars are utilized in sauces, salad dressings, canned and dehydrated soups, and cured meats as well.¹⁰ Extrinsic sugars are, therefore, present in these products and are detrimental to health if taken in high quantities.¹¹

Sugar-sweetened beverages are the most common source of added sugar and include fruit drinks, soft drinks, and energy/vitamin water drinks. They are non-alcoholic and contain sucrose and glucose as well as artificial sweeteners.⁷ Soda beverages prepared using carbonated water, flavors, and sucrose or high-fructose corn syrup (HFCS) or artificial sweeteners are consumed chiefly by adolescents and young adults.¹³

Sucrose is used normally in the formulation of cough drops, antibiotic syrups, vitamin tablets, and throat lozenges by pharmaceutical manufacturers. Several medicines, remarkably those prepared for children are provided in the form of sucrose-based syrup containing up to 70% of sugar.¹⁴

Different forms of added sugars

Added sugars are available in various forms such as white sugar, brown sugar, liquid sugar, and HFCS. White sugar comprises regular or white granulated sugar, confectioners’ or powdered sugar, fruit sugar, superfine sugar, baker’s special sugar, sanding sugar, and coarse sugar. Brown sugar includes light and dark, demerara sugar, turbinado sugar, muscovado sugar, and free-flowing brown sugar. Liquid sugars are liquid and inverted sugars.¹⁵ High fructose corn syrup is a corn sweetener that is increasingly used in the brewing industry, confectionery, and cereal products.⁴

Impact of added sugars on general health

Added sugar intake in excess may lead to various systemic conditions. Obesity, type 2 diabetes mellitus, cardiovascular diseases, renal diseases, non-alcoholic liver disease, and gout are all linked to sugar-sweetened beverage consumption.¹⁶

Unprocessed sugar and sugar-added foods are the main sources of excessive calorie intake. Studies have shown that greater consumption of sugars over a while leads to increased levels of obesity in children and adolescents.¹⁷ A sugar-rich diet in addition to physical inactivity causes overweight and obesity, thus, increasing the risk of hypertension, dyslipidemia, peripheral insulin resistance, and inflammation. Obesity will eventually lead to health loss across the entire bodily system.³

The link between sugar-sweetened beverages and type 2 diabetes mellitus is proposed by many potential mechanisms. Excessive sugar and HFCS content in sugar-sweetened beverages may enhance the risk of type 2 diabetes mellitus. The high dietary glycaemic load due to the SSBs results in inflammation, insulin resistance, and impaired function of beta cells in the pancreas.¹⁷

Sugar may also exhibit addictive effects due to the refinement processes which convert it into a chemical like substance. Sugar alters mood and yields druglike psychoactive effects as proven by certain animal studies.¹⁸ Many people claim that sweet foods produce cravings comparable to that of alcohol, cocaine, and cigarettes.^18,19 Consuming sugars for treating low blood glucose levels further contributes to sugar addiction.¹⁸

Role of added sugars, carbonated drinks, and fluoridated water consumption in dental caries

Dental caries is one of the most frequent noncommunicable diseases caused by several interconnected variables.^5,20 It is an infectious disease in which bacteria in the oral cavity ferment the carbohydrates, resulting in the acid generation and enamel dissolution.¹³ Diet plays a major role in the etiology of dental caries. The role of free or added sugar as a causal agent for dental caries is certain.²⁰

The surging consumption of carbonated drinks in developed countries, especially among adolescent populations is a potential risk factor for dental caries. Soft drinks contain about 10% sucrose and the pH of most soft drinks is acidic due to the carbonic and phosphoric acids in them. In acid beverage consumers, both the sugar content and the low pH of carbonated beverages have an impact on the development of dental caries.² High carbonated soft drink consumption was related to a high prevalence of dental caries among children and young adults.^21,22 Subjects with caries had a higher intake of soda pop, regular beverages, and sports drinks.²³

Studies have observed the association between fluoridated water exposure, added sugar consumption, and dental caries. Decayed, missing and filled teeth (DMFT) was higher in children who drank three or more sweetened drinks per day and had less fluoridated water exposure. The association between sweetened beverage consumption and dental caries in both deciduous and permanent teeth was attenuated with increased exposure to fluoridated water.²⁴ The deleterious effect of sugar consumption on children’s dental caries was compensated by frequent intake of fluoridated water.²⁵

Cariogenicity of added sugar

The chief microorganism responsible for the development of dental caries is Streptococcus mutans. It utilizes sucrose to form extracellular glycans using the glucosyltransferase enzyme which aids in dental plaque adherence to the enamel surface. Fructose or glucose are not utilized by S. mutans for extracellular glycan synthesis. The bonds between the glycans are robust. Hence, the porosities of the plaque are amplified which allows the diffusion of acids and sugars within the plaque, thereby, increasing the caries risk.²³ Other disaccharides are less cariogenic than sucrose.9 The greater fall in caries incidence in the US can be explained by an escalated use of HFCS sweeteners with a simultaneous reduction in sucrose.⁴

Factors affecting cariogenicity of added sugar

The prime factors affecting the cariogenicity of added sugars are frequency of ingestion, oral sugar clearance, and effective concentration of sucrose.

Frequency of ingestion

The frequency of consumption of sugars is one of the significant factors influencing cariogenicity. The process by which greater frequency of sugar ingestion leads to increased caries activity is expressed in terms of intra-plaque events. When added sugar is ingested frequently, even in a low concentration of 1.25%, the pH of the oral environment drops to 4 or 5.² Increased frequency of sugary drinks and meal intake among children was associated with greater DMFT.^8,25 Children who consumed snacks at least once a day were two times more likely to experience dental caries than those who rarely or never took their snacks in a day.²⁶ Dental caries progression from 6 to 18-year old was steadily and positively correlated with an increased array of sugar consumption along the life span.²⁷ Children who were fed SSBs more than 3 times per week at 10–12 months were more likely to get dental caries by 6 years of age (OR 1.83) than those who were never fed SSBs.²⁸

The consumption of added sugar during meals is not as deleterious as when consumed in between meals. Stephan and Miller explained that after a sugary diet, the pH drops within 30 minutes. Thus, further ingestion of sugar within 30 minutes is less harmful to oral health than ingestion after 30 minutes. This implies the significance of the frequency of sugar intake in the process of development of dental caries.²⁰

Oral sugar clearance

The duration of exposure and retention of sugar in the teeth are persuaded by the form of sugar intake.⁹ Retentive and sticky sweet foods may be more cariogenic than liquid sugars that have a limited contact time and are rapidly cleared from the oral cavity.² However, fluid intake patterns such as retaining sugar-sweetened beverages in the oral cavity for an extended time increase the odds of dental caries. Added sugar items such as candies, breath mints, and lollipops which are slow dissolving have a longer exposure period in the oral cavity as the sugars are constantly released during consumption. Prolonged retention of added sugars in the oral cavity may lead to sustained acid production and demineralization of teeth.⁹

The effective concentration of sucrose

Sucrose consumption increased considerably as a result of highly concentrated processed cane sugar, as did the concentration of sucrose in various food items. About 5% to 50% of sucrose concentration is present in processed foods and sweet snacks. The multi-enzyme system of plaque flora would become saturated due to the intake of such high sugar-containing foods which causes maximum acid production in the plaque. Any increase in substrate concentration at saturation level may extend the duration at which low pH levels are maintained but do not lead to a much drop in pH. Plaque saturation is most likely caused by the current level of sugar consumption, which occurs from the ingestion time of sweet foods until their elimination from the oral cavity. This explains the tangential relationship between total sugar content and dental caries. Conversely, intermittent and frequent usage of sucrose restores substrate concentration as it is depleted.²

Barriers to addressing added sugar intake

Sugar encompasses 17% of the total energy intake of children in the US based on 2011 to 2012 US National Health and Nutrition Examination Survey (NHANES) data. Beverage labels overestimate or underestimate sugar content in the product by about 10% and they are also difficult for consumers to infer.

Unhealthy food and beverage consumption among vulnerable populations are continuing to be subsidized by government nutrition programs. For example, the purchase of sugar-sweetened beverages is permitted by the US Supplemental Nutrition Assistance Program (SNAP). Due to political and logistic constraints, legislation limiting SNAP purchases is unlikely to succeed. Incentive-based techniques that provide government nutrition program users more flexibility in how funds are spent and subsidies to encourage healthy expenditure are both viable options.²⁹

The corporate members of the European Organisation for Caries Research (ORCA) are involved in the Dental Research Organization. These include confectionery companies and companies that sell sugary products. Oral health-care products such as toothbrushes, fluoridated toothpaste, and xylitol chewing gum are also the products of such companies. In such a way, these industries conceal the ill effects caused by the consumption of sugar products. There is evidence of the influence of industries in research. Industries have funded studies on the association of obesity with physical activity. They have also funded dental research to develop non-dietary interventions to control dental caries, including enzymes that break up dental plaque and a caries vaccine. Such industry-supported research agendas are augmented for industrial profits and not for the advancement of public health.³⁰

Clinical strategies for addressing added sugar in the prevention of dental caries

Studies have shown an association between added sugar intake and dental caries.^1,8,23 An increment in the amount, frequency, and duration of exposure to added sugar lays consumers at increased caries risk. Hence, it is crucial to address the cause.⁵

Added sugar intake can be assessed using various methods such as added sugar estimate formula,²¹ added sugar estimate questionnaires,³¹ food frequency questionnaires,²⁶ and block kids food frequency questionnaires.³² Caries risk assessment should include data regarding patients’ intake of sugar-sweetened beverages and other sources of added sugars. Comprehensive knowledge about caries promoting dietary habits and sources of sugar in patients is necessary to plan effective dietary advice. Dietary counseling for the parents to limit their child’s SSB intake should be imparted by dentists and other healthcare providers.²⁹ Excess consumption of carbonated soft drinks by young children is a risk indicator for dental caries and should be thwarted.¹³ Collaboration with nutritionists will serve the purpose of reducing added sugar intake.²⁹ Dietary guidelines for dental caries prevention grant a framework for health professionals to regulate added sugar intake.⁹

Policy measures for curtailing added sugar intake

The cost of treatment for dental caries sets a huge burden on healthcare budgets in most countries. Legislative initiatives are an effective means to reduce added sugar intake for addressing the global burden of dental caries. WHO recommends certain measures to tackle added sugar intake as follows: taxation on sugar-sweetened beverages and foods rich in added sugars, mandatory clear nutrition labeling on food products, restriction of sugar-sweetened beverages sale in schools and hospitals, regulation of marketing and advertising of foods rich in added sugars, increasing public awareness, and access to pure water as a tooth-friendly drink. Thus, to reduce the permanent risk of dental caries in a lifetime, the added sugar intake should be as low as feasible.⁵

Conclusion

Contemporary changes have occurred in the type, amount, and behavior of added sugar consumption. The increased rate of dental caries is the consequence of the shift in sugar consumption in oral health. It is triggered by lifetime intake of added sugars, hence even a minor cutback in the intake during childhood is of worth in later life. Promoting a healthy dietary environment and restricting the consumption of foods and drinks with added sugar would be important for reducing excessive intake of added sugar, especially among children and adolescents. Implementation of community-based preventive oral health programs on healthy diet and practices of adequate oral hygiene should be promoted.

Conflict of interest

The authors declare that they have no conflict of interest.

Financial support and sponsorship

Nil