Sweet treat consumption in school-aged children: relationships between excess weight, dental caries and saliva microbiota

Globally excess weight and dental caries are highly prevalent chronic conditions both in children and adults, suggested as sharing risk factors, amongst them dietary sugar. Notably, sugar intake in children and adolescents appears high in many developed countries. The oral microbiota – that is, the microbial communities in the oral cavity – contribute to oral health as well as contributing to systemic health, and changes to the saliva microbiota might depend upon sugar consumption. This doctoral thesis aimed to 1) examine the relationship between the consumption frequency of foods and drinks generally high in added sugar (‘sweet treats’) and the risk of excess weight, 2) examine changes in sweet treat consumption patterns during early adolescence and whether these changes associate with changes in weight status and central obesity or the risk of developing excess weight or central obesity, 3) examine the relationship of sweet treat consumption frequency and other dietary factors to the risk of caries experience and 4) assess the diversity, composition and functional capacities of the saliva microbiota in children with low and high frequency levels of sweet treat consumption. The studies in this doctoral thesis consist of four original research publications and utilise material from the Finnish Health in Teens (Fin-HIT) study. The Fin-HIT is an ongoing prospective cohort of over 11 000 children aged mostly 9–12 years at enrolment. Baseline data collection was conducted between 2011 and 2014, and children were followed for nearly three years. Study I (n = 8461), study III (n = 6660) and study IV (n = 453) utilised cross-sectional data, whereas study II (n = 4237) was longitudinal. The research data includes self-reported questionnaire data on the consumption of indicative food items and other lifestyle factors, measured and self-reported anthropometrics as well as saliva samples. Sweet treats consisted of chocolate and sweets, sweet pastries, biscuits and cookies, ice cream, sugary soft drinks and sugary juice drinks. A sweet treat index (STI) was calculated to indicate the sum of the weekly consumption frequencies of sweet treats. Based on the STI and change in STI, children fell into low, medium and high as well as decreased, stable and increased STI groups, respectively. Weight status was defined as thin, normal weight, overweight or obese (that is, excess weight) using age- and sex-specific cut-offs, and as without central obesity and with central obesity based on the waist–height ratio (WHtR). The decayed, missing and filled teeth (DMFT) index for permanent teeth was used to indicate a history of cavitated caries lesions (caries experience). The saliva microbiota was characterised using 16S rRNA gene sequencing. We performed statistical analyses using the chi-square test, t-test, analysis of variance (ANOVA), logistic regression, Cox regression, permutational multivariate analysis of variance (PERMANOVA) and general linear model. Less than one in six children had excess weight. Children with a low consumption frequency of sweet treats were at an increased risk of having excess weight, whereas children with a high consumption were at an increased risk of thinness. On average, STI decreased during early adolescence, although the consumption frequency of chocolate and sweets increased in girls and boys, and that of sugar-sweetened soft drinks increased in boys. Similarly, decreasing trends in the mean STI were observed in groups of children who developed excess weight or central obesity. A decrease in the STI was associated with the risk of developing excess weight. Two-thirds of children had no caries experience. A high sweet treat consumption associated with an increased risk of a caries experience, whilst a low consumption associated with a decreased risk. Diversity in the saliva microbiota did not differ between a low and high sweet treat consumption, although differences in the composition and functional capacities were observed; several bacterial genera were differentially abundant, and pathways relating to nitrate reduction and gondoate biosynthesis were enriched in the saliva of children with the highest consumption frequency of sweet treats. The highest consumption frequency of sweet treats did not associate with excess weight cross-sectionally nor longitudinally, suggesting that sugary product consumption alone may not be relevant as a target of obesity prevention programmes amongst school-aged children. Although the overall sweet treat consumption frequency decreased during early adolescence, the increase in the consumption frequency of chocolate and sweets and sugary soft drinks requires attention. Specifically, we observed differences between girls’ and boys’ consumption patterns. A high consumption frequency of sweet treats associated positively with the risk of caries experience, highlighting the need to focus on sugar consumption to prevent caries even in an affluent Nordic country. Moreover, findings regarding the different saliva microbiota profiles in children with the lowest and highest sweet treat consumption frequencies can be utilised in future studies to further our knowledge about the influence of sugary diets on the saliva microbiota and, consequently, on oral and systemic health.